Theistic Evolution

Theistic evolution or evolutionary creation is a concept that asserts that classical religious teachings about God are compatible with the modern scientific understanding about biological evolution. In short, theistic evolutionists believe that there is a God, that God is the creator of the material universe and (by consequence) all life within, and that biological evolution is simply a natural process within that creation. Evolution, according to this view, is simply a tool that God employed to develop human life.

Theistic evolution is not a scientific theory, but a particular view about how the science of evolution relates to religious belief and interpretation. Theistic evolution supporters can be seen as one of the groups who reject the conflict thesis regarding the relationship between religion and science – that is, they hold that religious teachings about creation and scientific theories of evolution need not contradict. Proponents of this view are sometimes described as Christian Darwinists.[1][2]


The term was used by National Center for Science Education executive director Eugenie Scott to refer to the part of the overall spectrum of beliefs about creation and evolution holding the theological view that God creates through evolution. It covers a wide range of beliefs about the extent of any intervention by God, with some approaching deism in rejecting continued intervention. Others see intervention at critical intervals in history in a way consistent with scientific explanations of speciation, but with similarities to the ideas of Progressive Creationism that God created “kinds” of animals sequentially.[3]


This view is generally accepted by major Christian churches, including the Catholic Church, Eastern Orthodox Church and some mainline Protestant denominations; virtually all Jewish denominations; and other religious groups that lack a literalist stance concerning some holy scriptures. Various biblical literalists have accepted or noted openness to this stance, including theologian B.B. Warfield and evangelist Billy Graham.

With this approach toward evolution, scriptural creation stories are typically interpreted as being allegorical in nature. Both Jews and Christians have considered the idea of the creation history as an allegory (instead of a historical description) long before the development of Darwin’s theory. An example in Christianity would be the earlier writings by St. Augustine (4th century), though he later rejected allegory in favor of literal interpretation. By this Augustine meant that in Genesis 1 the terms “light”, “day”, and “morning” hold a spiritual, rather than physical, meaning, and that this spiritual morning is just as literal as physical morning. Augustine recognizes that the creation of a spiritual morning is as much a historical event as the creation of physical light.[4] [In later work, Augustine said: “…there are some who think that only the world was made by God and that everything else is made by the world according to his ordination and command, but that God Himself makes nothing”.[5]] Three noted Jewish examples are that of the writings of Philo of Alexandria (1st century),[6] Maimonides (12th century) and Gersonides (13th century).[7][8]

Theistic evolutionists argue that it is inappropriate to use Genesis as a scientific text, since it was written in a pre-scientific age and originally intended for religious instruction; as such, seemingly chronological aspects of the creation accounts should be thought of in terms of a literary framework. Theistic evolutionists may believe that creation is not literally a week long process but a process beginning in the time of Genesis and continuing through all of time, including today. This view affirms that God created the world and was the primary causation of our being, while scientific changes such as evolution are part of “creatio continua” or continuing creation which is still occurring in the never ending process of creation. This is one possible way of interpreting biblical scriptures, such as Genesis, that seem to be in opposition to scientific theories, such as evolution.[9]

Religious Differences on the Question of Evolution (United States, 2007)
Percentage who agree that evolution is the best explanation for the origin of human life on earth
Pew Forum[10]













Mainline Protestant




Hist. Black Protest.


Evang. Protestant




Jehovah’s Witness


Total U.S. population



….creationism has come to mean some fundamentalistic, literal, scientific interpretation of Genesis. Judaic-Christian faith is radically creationist, but in a totally different sense. It is rooted in a belief that everything depends upon God, or better, all is a gift from God.

—Fr George Coyne, Director, Vatican Observatory, 1978-2006

Theistic evolution holds that the theist’s acceptance of evolutionary biology is not fundamentally different from the acceptance of other sciences, such as astronomy or meteorology. The latter two are also based on a methodological assumption of naturalism to study and explain the natural world, without assuming the existence or nonexistence of the supernatural. In this view, it is held both religiously and scientifically correct to reinterpret ancient religious texts in line with modern-day scientific findings about evolution. St. Anselm described theology as “Faith seeking understanding”[11] and theistic evolutionists believe that this search for understanding extends to scientific understanding. In light of this view, authors writing on the subject, such as Ted Peters and Martinez Hewlett, say that “The best science and our best thinking about God belong together.”[9] Peters and Hewlett see science as a means of evaluating, understanding, and using to our benefit the intricacies of the world that God has created for us.

Spectrum of Viewpoints

Many religious organizations accept evolutionary theory, though their related theological interpretations vary. Additionally, individuals or movements within such organizations may not accept evolution, and stances on evolution may have adapted (or evolved) throughout history.


In the Bahá’í Faith, `Abdul-Bahá, the son of the founder of the religion, wrote about the origin of life. A fundamental part of `Abdul-Bahá’s teachings on evolution is the belief that all life came from the same origin: “the origin of all material life is one…”[12] He states that from this sole origin, the complete diversity of life was generated: “Consider the world of created beings, how varied and diverse they are in species, yet with one sole origin”[13] He explains that a slow, gradual process led to the development of complex entities:

“[T]he growth and development of all beings is gradual; this is the universal divine organization and the natural system. The seed does not at once become a tree; the embryo does not at once become a man; the mineral does not suddenly become a stone. No, they grow and develop gradually and attain the limit of perfection”[14]


Evolution contradicts a literalistic interpretation of Genesis; however, according to Roman Catholicism and most contemporary Protestant Churches, biblical literalism in the creation account is not mandatory. Christians have considered allegorical interpretations of Genesis since long before the development of Darwin‘s theory of evolution, or Hutton‘s principle of uniformitarianism. A notable example is St. Augustine (4th century), who, on theological grounds, argued that everything in the universe was created by God in the same instant, and not in six days as a plain reading of Genesis would require.[4] Modern theologians such as Meredith G. Kline and Henri Blocher have advocated what has become known as the literary framework interpretation of the days of Genesis.

Contemporary Christian denominations

All of the traditional mainline Protestant denominations support or accept theistic evolution. For example, on 12 February 2006, the 197th anniversary of Charles Darwin‘s birth was commemorated by “Evolution Sunday” where the message that followers of Christ do not have to choose between biblical stories of creation and evolution was taught in classes and sermons at many Methodist, Lutheran, Episcopalian, Presbyterian, Unitarian, Congregationalist, United Church of Christ, Baptist and community churches.[15]

Additionally, the National Council of Churches USA has issued a teaching resource to “assist people of faith who experience no conflict between science and their faith and who embrace science as one way of appreciating the beauty and complexity of God’s creation.” This resource cites the Episcopal Church, according to whom the stories of creation in Genesis “should not be understood as historical and scientific accounts of origins but as proclamations of basic theological truths about creation.”[16]

The positions of particular denominations are discussed below.


Anglicans (including the Episcopal Church in the United States of America, the Church of England and others) believe that the Bible “contains all things necessary to salvation,” while believing that “science and Christian theology can complement one another in the quest for truth and understanding.” Specifically on the subject of creation/evolution, some Anglicans view “Big Bang cosmology” as being “in tune with both the concepts of creation out of nothing and continuous creation.” Their position is clearly set out in the Catechism of Creation Part II: Creation and Science.[17] In an interview, the Archbishop of Canterbury Dr Rowan Williams expressed his thought that “creationism is, in a sense, a kind of category mistake, as if the Bible were a theory like other theories. Whatever the biblical account of creation is, it’s not a theory alongside theories… My worry is creationism can end up reducing the doctrine of creation rather than enhancing it.”[18] His view is that creationism should not be taught in schools.

United Methodist Church

The United Methodist Church affirms a Creator God and supports the scientific study of creation.

“We recognize science as a legitimate interpretation of God’s natural world. We affirm the validity of the claims of science in describing the natural world and in determining what is scientific. We preclude science from making authoritative claims about theological issues and theology from making authoritative claims about scientific issues. We find that science’s descriptions of cosmological, geological, and biological evolution are not in conflict with theology.” [19]

Church of the Nazarene

The Church of the Nazarene, an evangelical Christian denomination, sees “knowledge acquired by science and human inquiry equal to that acquired by divine revelation,” and, while the church “‘believes in the Biblical account of creation’ and holds that God is the sole creator, it allows latitude ‘regarding the “how” of creation.'”[20]

While Richard G. Colling, author of Random Designer[21] and professor at Olivet Nazarene University, received criticism from elements within the denomination in 2007 for his book (published in 2004),[20] Darrel R. Falk of Point Loma Nazarene published a similar book in 2004,[22] and Karl Giberson of Eastern Nazarene, the first Nazarene scholar to publish with Oxford University Press, has published four books since 1993 on the tensions between science and religion,[23] including his most recently published Saving Darwin.[20]

Theologians of note in the denomination whose work on science and religion shows the promise of cooperation include Thomas Jay Oord (Science of Love, The Altruism Reader), Michael Lodahl (God of Nature and of Grace), and Samuel M. Powell (Participating in God). These theologians see no major problem reconciling theology with the general theory of evolution.[citation needed]

The Nazarene Manual, a document crafted to provide Biblical guidance and denominational expression for Church members, states: “The Church of the Nazarene believes in the biblical account of creation (“In the beginning God created the heavens and the earth . . .”—Genesis 1:1). We oppose any godless interpretation of the origin of the universe and of humankind. However, the church accepts as valid all scientifically verifiable discoveries in geology and other natural phenomena, for we firmly believe that God is the Creator. (Articles I.1., V. 5.1, VII.) (2005)[24]

Eastern Orthodox Church

The Eastern Orthodox Church is divided in two large categories, which might be labeled as compatibilism and dualism.

On the one hand, compatibilists hold that science and theology are compatible and view them as complementary revelations of God. As God is the source of both his specific revelation of himself in the Christian faith and the source of the general revelation of himself in nature, the findings of science and theology cannot really contradict; the contradictions must be merely apparent and a resolution possible which is faithful to the truth of God’s revelation. Nicozisin (Father George) is a compatibilist.[25]

On the other hand, dualists hold that science can be incompatible with faith. They usually argue either that science is philosophically based on a kind of naturalism or that God’s specific revelation is infallible and therefore trumps the findings of human reason in the case of any conflict between them. This is often based on a suspicion of human reason to arrive at reliable conclusions in the first place. Their stance is somewhat similar to Averroism, in that there is one truth, but it can be arrived at through (at least) two different paths, namely Philosophy and Religion. Bufeev, S. V, is a dualist, preferring to see the spiritual level above the mechanical, physico-chemical, or biological levels; he attributes discrepancies between spiritual matters and scientific matters to be because of the purely naturalistic views of evolutionists.[26]

Roman Catholic Church

The position of the Roman Catholic Church on the theory of evolution has changed over the last two centuries from a large period of no official mention, to a statement of neutrality in the 1950s, to limited guarded acceptance in recent years, rejecting the materialistic and reductionist philosophies behind it, and insisting that the human soul was immediately infused by God, and the reality of a single human ancestor (commonly called monogenism) for all of mankind. The Church does not argue with scientists on matters such as the age of the earth and the authenticity of the fossil record, seeing such matters as outside its area of expertise. Papal pronouncements, along with commentaries by cardinals, indicate that the Church is aware of the general findings of scientists on the gradual appearance of life. Under Cardinal Joseph Ratzinger, the International Theological Commission published a paper accepting the big bang of 15 billion years ago and the evolution of all life including humans from the microorganisms that formed approximately 4 billion years ago.[27] The Vatican has no official teaching on this matter except for the special creation of the human soul.[28] The Pontifical Biblical Commission issued a decree ratified by Pope Pius X on June 30, 1909 stating that special creation applies to humans and not other species. [29]


Deism is belief in a God or first cause based on reason, rather than on faith or revelation. Most deists believe that God does not interfere with the world or create miracles. Some deists believe that a Divine Creator initiated a universe in which evolution occurred, by designing the system and the natural laws, although many deists believe that God also created life itself, before allowing it to be subject to evolution. They find it to be undignified and unwieldy for a deity to make constant adjustments rather than letting evolution elegantly adapt organisms to changing environments. Other deists take the stronger position that God ceased to exist after setting in motion the laws of the universe.

One recent convert to deism was philosopher and professor Antony Flew, who became a deist in December 2004. Professor Flew, a former atheist, later argued that recent research into the origins of life supports the theory that some form of intelligence was involved. Whilst accepting subsequent Darwinian evolution, Flew argued that this cannot explain the complexities of the origins of life. He also stated that the investigation of DNA “has shown, by the almost unbelievable complexity of the arrangements which are needed to produce [life], that intelligence must have been involved.”[30] He subsequently clarified this statement in an interview with Joan Bakewell for BBC Radio 4 in March 2005: “What I was converted to was the existence of an Aristotelian God, and Aristotle’s God had no interest in human affairs at all.”[31]

Evolutionary creation

Evolutionary creation[32] (EC, also referred to by some observers as evolutionary creationism) states that the Creator God uses evolution to bring about his plan. Eugenie Scott states in Evolution Vs. Creationism that it is a type of evolution rather than creationism, despite its name, and that it is “hardly distinguishable from Theistic Evolution”.[2] Scott, citing personal communication with prominent evolutionary creationist Denis Lamoureux, states that “the differences between EC and theistic evolution lie not in science but in theology, with EC being held by more conservative (Evangelical) Christians, who view God as being more actively involved in evolution than do most theistic evolutionists”.[2]


Hindu views on evolution include a range of viewpoints in regards to evolution, creationism, and the origin of life within the traditions of Hinduism. The accounts of the emergence of life within the universe vary in description, but classically the deity called Brahma, from a Trimurti of three deities also including Vishnu and Shiva, is described as performing the act of ‘creation’, or more specifically of ‘propagating life within the universe’ with the other two deities being responsible for ‘preservation’ and ‘destruction’ (of the universe) respectively.[33] Some Hindu schools do not treat the scriptural creation myth literally and often the creation stories themselves do not go into specific detail, thus leaving open the possibility of incorporating at least some theories in support of evolution. Some Hindus find support for, or foreshadowing of evolutionary ideas in scriptures, namely the Vedas.[34]

Day and Night of Brahma

Science writers Carl Sagan and Fritjof Capra have pointed out similarities between the latest scientific understanding of the age of the universe, and the Hindu concept of a “day and night of Brahma”, which is much closer to the current known age of the universe than other creation myths. The days and nights of Brahma posit a view of the universe that is divinely created, and is not strictly evolutionary, but an ongoing cycle of birth, death, and rebirth of the universe. According to Sagan:

The Hindu religion is the only one of the world’s great faiths dedicated to the idea that the Cosmos itself undergoes an immense, indeed an infinite, number of deaths and rebirths. It is the only religion in which time scales correspond to those of modern scientific cosmology. Its cycles run from our ordinary day and night to a day and night of Brahma, 8.64 billion years long, longer than the age of the Earth or the Sun and about half the time since the Big Bang.[35]

Capra, in his popular book The Tao of Physics, wrote that:

This idea of a periodically expanding and contracting universe, which involves a scale of time and space of vast proportions, has arisen not only in modern cosmology, but also in ancient Indian mythology. Experiencing the universe as an organic and rhythmically moving cosmos, the Hindus were able to develop evolutionary cosmologies which come very close to our modern scientific models.[36]

Daśāvatāras and evolution

British geneticist and evolutionary biologist, J B S Haldane, observed that the Dasavataras (ten principal avatars of Lord Vishnu) are a true sequential depiction of the great unfolding of evolution. The avatars of Vishnu show an uncanny similarity to the biological theory of evolution of life on earth.[37][not in citation given]





First avatar is a fish, one which is creature living in water.

If we compare it with biological evolution on different Geological Time Scale first developed life was also in the form of fish which originated during Cambrian period.


Second avatar was in the form of Tortoise (reptiles).

In geology also first reptiles comes as second important evolution which originated in Mississippian period just after Amphibians.


Third avatar was in the form of Boar.

Evolution of the amphibian to the land animal.


The Man-Lion (Nara= man, simha=lion) was the fourth avatar.

But in geology no such evidences are mentioned. It may have been related with Ape Man The term may sometimes refer to extinct early human ancestors.


Fifth Avatar is the dwarf man.

It may be related with the first man originated during Pliocene. It may be related with Neanderthals. Neanderthals were generally only 12 to 14 cm (4½–5½ in) shorter than modern humans, contrary to a common view of them as “very short” or “just over 5 feet”.


The man with an axe was the sixth avatar.

It has the similarities with the first modern man originated during Quaternary period or the man of Iron Age.

Lord Rama, Lord Krishna and Lord Buddha were the seventh, eighth and ninth other avatars of Lord Vishnu. It indicates the physical and mental changes and evolution in the man from its time of appearance.


Many Muslims believe in evolutionary creationism, especially among mainstream Sunni and Shi’a Muslim communities.

Some literalist Muslims reject origin of species from a common ancestor by evolution as incompatible with the Qur’an. However, even amongst Muslims who accept evolution, many believe that humanity was a special creation by God. For example, Shaikh Nuh Ha Mim Keller, an American Muslim and specialist in Islamic law has argued in Islam and Evolution[38] that a belief in macroevolution is not incompatible with Islam, as long as it is accepted that “Allah is the Creator of everything” (Qur’an 13:16) and that Allah specifically created humanity (in the person of Adam; Qur’an 38:71-76). Shaikh Keller states in his conclusion however:

“As for claim that man has evolved from a non-human species, this is unbelief (kufr) no matter if we ascribe the process to Allah or to “nature,” because it negates the truth of Adam’s special creation that Allah has revealed in the Qur’an. Man is of special origin, attested to not only by revelation, but also by the divine secret within him, the capacity for ma’rifa or knowledge of the Divine that he alone of all things possesses. By his God-given nature, man stands before a door opening onto infinitude that no other creature in the universe can aspire to. Man is something else.”


In general, three of the four major denominations of American Judaism (Reconstructionist, Reform, and Conservative) accept theistic evolution. Within Orthodoxy, there is much debate about the issue. Most Modern Orthodox groups accept theistic evolution and most Ultra-Orthodox groups do not. This disagreement was most vociferous in the Natan Slifkin controversy which arose when a number of prominent Ultra-Orthodox Rabbis banned books written by Rabbi Natan Slifkin which explored the idea of theistic evolution within Jewish tradition. These Rabbis forming part of Jewish opposition to evolution considered that his books were heresy as they indicated that the Talmud is not necessarily correct about scientific matters such as the age of the Earth.

Advocates of theistic evolution within Judaism follow two general approaches. Either the creation account in the Torah is not to be taken as a literal text, but rather as a symbolic work, or, alternatively, that the ‘days’ do not refer to 24-hour periods (justified by how the first day in the biblical account actually precedes the creation of the sun and earth by which 24 hour days are reckoned). In the latter view, Jewish scholars point out how the order of creation in Genesis corresponds to the scientific description of the development of life on Earth—the sun, then earth, then oceans, then oceanic plant life, fish preceding land-based life, with mammals and finally humans last—and in no way specifies the method of creation in a manner prohibitive of evolution.

Karaite Judaism is a Jewish a movement which is distinct in that they do not accept the Talmud (a series of Rabbinic commentaries) as law and follow the Hebrew scriptures as they are written. Karaites are currently divided on the question of evolution with many or most Karaite Jews leaning in favor of Theistic Evolution.

The Samaritans, who do not consider themselves to be Jewish but who hold similar beliefs, generally accept Theistic Evolution.


Evolutionary biologists who were also theists

Although evolutionary biologists have often been agnostics (most notably Thomas Huxley and Charles Darwin) or atheists (most notably Richard Dawkins), from the outset many have had a belief in some form of theism. These have included Alfred Russel Wallace (1823–1913), who in a joint paper with Charles Darwin in 1858, proposed the theory of evolution by natural selection. Wallace, in his later years, was effectively a deist who believed that “the unseen universe of Spirit” had interceded to create life as well as consciousness in animals and (separately) in humans. Darwin had a longstanding close friendship with the American botanist Asa Gray who was a leading supporter of Darwin’s theory, and a devout Presbyterian.[39] Gray wrote a series of essays on the relationship of natural selection to religious belief and natural theology, and supported the views of theologians who said that design through evolution was inherent in all forms of life.[40] Darwin had Gray and Charles Kingsley in mind when he wrote that “It seems to me absurd to doubt that a man may be an ardent theist & an evolutionist”.[41]

An early example of this kind of approach came from computing pioneer Charles Babbage who published his unofficial Ninth Bridgewater Treatise in 1837, putting forward the thesis that God had the omnipotence and foresight to create as a divine legislator, making laws (or programs) which then produced species at the appropriate times, rather than continually interfering with ad hoc miracles each time a new species was required.

Pierre Teilhard de Chardin (1881–1955) was a noted geologist and paleontologist as well as a Jesuit Priest who wrote extensively on the subject of incorporating evolution into a new understanding of Christianity. Initially suppressed by the Roman Catholic Church, his theological work has had considerable influence and is widely taught in Catholic and most mainline Protestant seminaries.

Both Ronald Fisher (1890–1962) and Theodosius Dobzhansky (1900–1975), were Christians and architects of the modern evolutionary synthesis. Dobzhansky, a Russian Orthodox, wrote a famous 1973 essay entitled Nothing in Biology Makes Sense Except in the Light of Evolution espousing evolutionary creationism:

“I am a creationist and an evolutionist. Evolution is God’s, or Nature’s, method of creation. Creation is not an event that happened in 4004 BC; it is a process that began some 10 billion years ago and is still under way… Does the evolutionary doctrine clash with religious faith? It does not. It is a blunder to mistake the Holy Scriptures for elementary textbooks of astronomy, geology, biology, and anthropology. Only if symbols are construed to mean what they are not intended to mean can there arise imaginary, insoluble conflicts… the blunder leads to blasphemy: the Creator is accused of systematic deceitfulness.”

In the realm of biology and theology, the saying coined by Thomas Jay Oord is perhaps appropriate: “The Bible tells us how to find abundant life, not the details of how life became abundant.”

Contemporary advocates of theistic evolution

Contemporary biologists and geologists who are Christians and theistic evolutionists include:



Philosophers, theologians, and physical scientists who have supported the evolutionary creationist model include:




The major criticism of theistic evolution by non-theistic evolutionists focuses on its essential belief in a supernatural creator. These proponents argue that by the application of Occam’s razor, sufficient explanation of the phenomena of evolution is provided by natural processes (in particular, natural selection), and the intervention or direction of a supernatural entity is not required, simply adding another variable or assumption to the theory of evolution. Evolutionary biologist Richard Dawkins considers theistic evolution as a superfluous attempt to “smuggle God in by the back door”.[43]

Young Earth creationists criticise theistic evolution on theological grounds, finding it hard to reconcile the nature of a loving God with the process of evolution, in particular, the existence of death and suffering before the Fall of Man. They consider that it undermines central biblical teachings by regarding the creation account as a myth, a parable, or an allegory, instead of believing that it is historical. They also fear that a capitulation to what they call “atheisticnaturalism will confine God to the gaps in scientific explanations, undermining biblical doctrines, such as God’s incarnation through Christ.[44] Theistic evolutionists deny these claims.

Relationship to Intelligent Design

A number of notable proponents of theistic evolution, including Kenneth R. Miller, John Haught, Michael Dowd, and Francis Collins, are critics of Intelligent design.


1.       ^ Numbers, Ronald (November 30, 2006). The Creationists: From Scientific Creationism to Intelligent Design, Expanded Edition. Harvard University Press. ISBN 0-674-02339-0. pp 34-38

2.       ^ a b c Evolution Vs. Creationism, Eugenie Scott, Niles Eldredge, p62-63

3.       ^ The Creation/Evolution Continuum by Eugenie Scott, December 2000, National Center for Science Education

4.       ^ a b Davis A. Young, “The Contemporary Relevance of Augustine’s View of Creation” from Perspectives on Science and Christian Faith 40.1

5.       ^ Taylor, JH (trans) (1982) “St. Augustine. The Literal Meaning of Genesis”, Paulist Press, New York, p171

6.       ^ “Allegorical Interpretation, I” from The Works of Philo Judaeus, translated by C.D. Yonge at the Wayback Machine

7.       ^ The Guide for the Perplexed 2:17

8.       ^ Milchamot Hashem 6:8

9.       ^ a b Can You Believe in God and Evolution, Ted Peters and Matrinez Hewlett

10.    ^ Religious Groups: Opinions of Evolution, Pew Forum (conducted in 2007, released in 2008)

11.    ^ St Anselm (1077–1078). “Preface”. Proslogion.

12.    ^ Effendi 1912, p. 350

13.    ^ `Abdu’l-Bahá 1912, pp. 51–52

14.    ^ `Abdu’l-Bahá 1908, pp. 198–99

15.    ^ Churches urged to challenge Intelligent Design -20/02/06

16.    ^ Science, Religion, and the Teaching of Evolution in Public School Science Classes (pdf), The National Council of Churches Committee on Public Education and Literacy, Teaching Evolution, March 2006

17.    ^ Catechism of Creation Part II: Creation and Science

18.    ^ The Guardian, March 21, 2006

19.    ^ [1] The Book of Discipline of The United Methodist Church – 2008, The United Methodist Publishing House.

20.    ^ a b c “Can God Love Darwin, Too?” by Sharon Begley, Newsweek, Sept. 17, 2007 issue

21.    ^ Random Designer: Created from Chaos to Connect with the Creator, Browning Press, 2004, ISBN 0-9753904-0-6

22.    ^ Coming to Peace with Science: Bridging the Worlds Between Faith and Biology, InterVarsity Press, 2004, ISBN 0-8308-2742-0

23.    ^ Worlds Apart: The Unholy War between Religion and Science, Beacon Hill Press, 1993 ISBN 0-8341-1504-2
With Donald Yerxa, Species of Origins: America’s Search for a Creation Story, Rowman & Littlefield Publishers, Inc., 2002 ISBN 0-7425-0764-5
With Mariano Artigas, The Oracles of Science: Celebrity Scientist Versus God and Religion, Oxford University Press, 2006 ISBN 0-19-531072-1

24.    ^ Manual, p.371

25.    ^

26.    ^

27.    ^ “Communion and Stewardship: Human Persons Created in the Image of God.” Vatican: The Holy See. International Theological Commission, 2002. Web. 19 Mar. 2012. ch.3 p.63 <>.

28.    ^ “Communion and Stewardship: Human Persons Created in the Image of God”. International Theological Commission. La Civilità Cattolica. July 2004. pp. 254–286.

29.    ^ Stenson, James B. (March 1984). “Evolution: A Catholic Perspective”. Catholic Position Papers, Series A, Number 116. Ashiya-Shi, Japan: Seido Foundation for the Advancement of Education.

30.    ^ Atheist Philosopher, 81, Now Believes in God | LiveScience

31.    ^ BBC interview, Professor Antony Flew March 22, 2005.

32.    ^ Evolutionary creation, Denis Lamoureux

33.    ^ “Religion & Ethics-Hinduism”. BBC. Retrieved 2008-12-26.

34.    ^ Moorty, J.S.R.L.Narayana (May 18–21, 1995). “Science and spirituality: Any Points of Contact? The Teachings of U.G.Krishnamurti: A Case Study”. Krishnamurti Centennial Conference. Retrieved 2008-12-26.

35.    ^ Sagan, Carl (1985). Cosmos. Ballantine Books. ISBN 978-0-345-33135-9. p. 258.

36.    ^ Capra, Fritjof (1991). Tao of Physics. Shambhala. ISBN 978-0-87773-594-6. p. 198

37.    ^

38.    ^ Evolution and Islam

39.    ^ “Historical Resources”. Darwin Correspondence Project. 2009. Retrieved 2009-12-14.

40.    ^ “Essays & reviews by Asa Gray”. Darwin Correspondence Project. Retrieved 2009-12-14.
Asa Gray (January 15, 1874). “Essay: Evolution & theology”. Darwin Correspondence Project. The Nation. Retrieved 2009-12-14.

41.    ^ “Letter 12041 — Darwin, C. R. to Fordyce, John, 7 May 1879”. Darwin Correspondence Project. Retrieved 2009-12-14.

42.    ^ Pope John Paul II, “Truth Cannot Contradict Truth”, New Advent, ed. Kevin Knight, 15 Feb 2009 <>

43.    ^ Numbers(2006) p374

44.    ^ 10 dangers of theistic evolution

Natural Selection

Natural selection is the gradual, nonrandom process by which biological traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution.

Variation exists within all populations of organisms. This occurs partly because random mutations cause changes in the genome of an individual organism, and these mutations can be passed to offspring. Throughout the individuals’ lives, their genomes interact with their environments to cause variations in traits. (The environment of a genome includes the molecular biology in the cell, other cells, other individuals, populations, species, as well as the abiotic environment.) Individuals with certain variants of the trait may survive and reproduce more than individuals with other variants. Therefore the population evolves. Factors that affect reproductive success are also important, an issue that Charles Darwin developed in his ideas on sexual selection, for example.

Natural selection acts on the phenotype, or the observable characteristics of an organism, but the genetic (heritable) basis of any phenotype that gives a reproductive advantage will become more common in a population (see allele frequency). Over time, this process can result in populations that specialize for particular ecological niches and may eventually result in the emergence of new species. In other words, natural selection is an important process (though not the only process) by which evolution takes place within a population of organisms. As opposed to artificial selection, in which humans favour specific traits, in natural selection the environment acts as a sieve through which only certain variations can pass.

Natural selection is one of the cornerstones of modern biology. The term was introduced by Darwin in his influential 1859 book On the Origin of Species,[1] in which natural selection was described as analogous to artificial selection, a process by which animals and plants with traits considered desirable by human breeders are systematically favored for reproduction. The concept of natural selection was originally developed in the absence of a valid theory of heredity; at the time of Darwin’s writing, nothing was known of modern genetics. The union of traditional Darwinian evolution with subsequent discoveries in classical and molecular genetics is termed the modern evolutionary synthesis. Natural selection remains the primary explanation for adaptive evolution.

General Principles

Morpha typica and morpha carbonaria, morphs of the peppered moth resting on the same tree. The light-colored morpha typica (below the bark’s scar) is hard to see on this pollution-free tree, camouflaging it from predators such as Great Tits.

Natural variation occurs among the individuals of any population of organisms. Many of these differences do not affect survival (such as differences in eye color in humans), but some differences may improve the chances of survival of a particular individual. A rabbit that runs faster than others may be more likely to escape from predators, and algae that are more efficient at extracting energy from sunlight will grow faster. Something that increases an animal’s survival will often also include its reproductive rate; however, sometimes there is a trade-off between survival and current reproduction. Ultimately, what matters is total lifetime reproduction of the animal.

For example, the peppered moth exists in both light and dark colors in the United Kingdom, but during the industrial revolution many of the trees on which the moths rested became blackened by soot, giving the dark-colored moths an advantage in hiding from predators. This gave dark-colored moths a better chance of surviving to produce dark-colored offspring, and in just fifty years from the first dark moth being caught, nearly all of the moths in industrial Manchester were dark. The balance was reversed by the effect of the Clean Air Act 1956, and the dark moths became rare again, demonstrating the influence of natural selection on peppered moth evolution.[2]

If the traits that give these individuals a reproductive advantage are also heritable, that is, passed from parent to child, then there will be a slightly higher proportion of fast rabbits or efficient algae in the next generation. This is known as differential reproduction. Even if the reproductive advantage is very slight, over many generations any heritable advantage will become dominant in the population. In this way the natural environment of an organism “selects” for traits that confer a reproductive advantage, causing gradual changes or evolution of life. This effect was first described and named by Charles Darwin.

The concept of natural selection predates the understanding of genetics, the mechanism of heredity for all known life forms. In modern terms, selection acts on an organism’s phenotype, or observable characteristics, but it is the organism’s genetic make-up or genotype that is inherited. The phenotype is the result of the genotype and the environment in which the organism lives (see Genotype-phenotype distinction).

This is the link between natural selection and genetics, as described in the modern evolutionary synthesis. Although a complete theory of evolution also requires an account of how genetic variation arises in the first place (such as by mutation and sexual reproduction) and includes other evolutionary mechanisms (such as genetic drift and gene flow), natural selection appears to be the most important mechanism for creating complex adaptations in nature.

Nomenclature and usage

The term natural selection has slightly different definitions in different contexts. It is most often defined to operate on heritable traits, because these are the traits that directly participate in evolution. However, natural selection is “blind” in the sense that changes in phenotype (physical and behavioral characteristics) can give a reproductive advantage regardless of whether or not the trait is heritable (non heritable traits can be the result of environmental factors or the life experience of the organism).

Following Darwin’s primary usage[1] the term is often used to refer to both the evolutionary consequence of blind selection and to its mechanisms.[3][4] It is sometimes helpful to explicitly distinguish between selection’s mechanisms and its effects; when this distinction is important, scientists define “natural selection” specifically as “those mechanisms that contribute to the selection of individuals that reproduce”, without regard to whether the basis of the selection is heritable. This is sometimes referred to as “phenotypic natural selection”.[5]

Traits that cause greater reproductive success of an organism are said to be selected for, whereas those that reduce success are selected against. Selection for a trait may also result in the selection of other correlated traits that do not themselves directly influence reproductive advantage. This may occur as a result of pleiotropy or gene linkage.[6]


Darwin’s illustrations of beak variation in the finches of the Galápagos Islands, which hold 13 closely related species that differ most markedly in the shape of their beaks. The beak of each species is suited to its preferred food, suggesting that beak shapes evolved by natural selection.

The concept of fitness is central to natural selection. In broad terms, individuals that are more “fit” have better potential for survival, as in the well-known phrase “survival of the fittest“. However, as with natural selection above, the precise meaning of the term is much more subtle. Modern evolutionary theory defines fitness not by how long an organism lives, but by how successful it is at reproducing. If an organism lives half as long as others of its species, but has twice as many offspring surviving to adulthood, its genes will become more common in the adult population of the next generation.

Though natural selection acts on individuals, the effects of chance mean that fitness can only really be defined “on average” for the individuals within a population. The fitness of a particular genotype corresponds to the average effect on all individuals with that genotype. Very low-fitness genotypes cause their bearers to have few or no offspring on average; examples include many human genetic disorders like cystic fibrosis.

Since fitness is an averaged quantity, it is also possible that a favorable mutation arises in an individual that does not survive to adulthood for unrelated reasons. Fitness also depends crucially upon the environment. Conditions like sickle-cell anemia may have low fitness in the general human population, but because the sickle-cell trait confers immunity from malaria, it has high fitness value in populations that have high malaria infection rates.

Types of selection

Natural selection can act on any heritable phenotypic trait, and selective pressure can be produced by any aspect of the environment, including sexual selection and competition with members of the same or other species. However, this does not imply that natural selection is always directional and results in adaptive evolution; natural selection often results in the maintenance of the status quo by eliminating less fit variants.

The unit of selection can be the individual or it can be another level within the hierarchy of biological organisation, such as genes, cells, and kin groups. There is still debate about whether natural selection acts at the level of groups or species to produce adaptations that benefit a larger, non-kin group. Likewise, there is debate as to whether selection at the molecular level prior to gene mutations and fertilization of the zygote should be ascribed to conventional natural selection because traditionally natural selection is an environmental and exterior force that acts upon a phenotype typically after birth. Some science journalists distinguish gene selection from natural selection by informally referencing selection of mutations as “pre-selection.”[7]

Selection at a different level such as the gene can result in an increase in fitness for that gene, while at the same time reducing the fitness of the individuals carrying that gene, in a process called intragenomic conflict. Overall, the combined effect of all selection pressures at various levels determines the overall fitness of an individual, and hence the outcome of natural selection.

The life cycle of a sexually reproducing organism. Various components of natural selection are indicated for each life stage.[8]

Natural selection occurs at every life stage of an individual. An individual organism must survive until adulthood before it can reproduce, and selection of those that reach this stage is called viability selection. In many species, adults must compete with each other for mates via sexual selection, and success in this competition determines who will parent the next generation. When individuals can reproduce more than once, a longer survival in the reproductive phase increases the number of offspring, called survival selection.

The fecundity of both females and males (for example, giant sperm in certain species of Drosophila)[9] can be limited via “fecundity selection”. The viability of produced gametes can differ, while intragenomic conflicts such as meiotic drive between the haploid gametes can result in gametic or “genic selection”. Finally, the union of some combinations of eggs and sperm might be more compatible than others; this is termed compatibility selection.

Sexual selection

It is useful to distinguish between “ecological selection” and “sexual selection”. Ecological selection covers any mechanism of selection as a result of the environment (including relatives, e.g. kin selection, competition, and infanticide), while “sexual selection” refers specifically to competition for mates.[10]

Sexual selection can be intrasexual, as in cases of competition among individuals of the same sex in a population, or intersexual, as in cases where one sex controls reproductive access by choosing among a population of available mates. Most commonly, intrasexual selection involves male–male competition and intersexual selection involves female choice of suitable males, due to the generally greater investment of resources for a female than a male in a single offspring. However, some species exhibit sex-role reversed behavior in which it is males that are most selective in mate choice; the best-known examples of this pattern occur in some fishes of the family Syngnathidae, though likely examples have also been found in amphibian and bird species.[11]

Some features that are confined to one sex only of a particular species can be explained by selection exercised by the other sex in the choice of a mate, for example, the extravagant plumage of some male birds. Similarly, aggression between members of the same sex is sometimes associated with very distinctive features, such as the antlers of stags, which are used in combat with other stags. More generally, intrasexual selection is often associated with sexual dimorphism, including differences in body size between males and females of a species.[12]

Examples of natural selection

Resistance to antibiotics is increased though the survival of individuals that are immune to the effects of the antibiotic, whose offspring then inherit the resistance, creating a new population of resistant bacteria.

A well-known example of natural selection in action is the development of antibiotic resistance in microorganisms. Since the discovery of penicillin in 1928, antibiotics have been used to fight bacterial diseases. Natural populations of bacteria contain, among their vast numbers of individual members, considerable variation in their genetic material, primarily as the result of mutations. When exposed to antibiotics, most bacteria die quickly, but some may have mutations that make them slightly less susceptible. If the exposure to antibiotics is short, these individuals will survive the treatment. This selective elimination of maladapted individuals from a population is natural selection.

These surviving bacteria will then reproduce again, producing the next generation. Due to the elimination of the maladapted individuals in the past generation, this population contains more bacteria that have some resistance against the antibiotic. At the same time, new mutations occur, contributing new genetic variation to the existing genetic variation. Spontaneous mutations are very rare, and advantageous mutations are even rarer. However, populations of bacteria are large enough that a few individuals will have beneficial mutations. If a new mutation reduces their susceptibility to an antibiotic, these individuals are more likely to survive when next confronted with that antibiotic.

Given enough time and repeated exposure to the antibiotic, a population of antibiotic-resistant bacteria will emerge. This new changed population of antibiotic-resistant bacteria is optimally adapted to the context it evolved in. At the same time, it is not necessarily optimally adapted any more to the old antibiotic free environment. The end result of natural selection is two populations that are both optimally adapted to their specific environment, while both perform substandard in the other environment.

The widespread use and misuse of antibiotics has resulted in increased microbial resistance to antibiotics in clinical use, to the point that the methicillin-resistant Staphylococcus aureus (MRSA) has been described as a “superbug” because of the threat it poses to health and its relative invulnerability to existing drugs.[13] Response strategies typically include the use of different, stronger antibiotics; however, new strains of MRSA have recently emerged that are resistant even to these drugs.[14]

This is an example of what is known as an evolutionary arms race, in which bacteria continue to develop strains that are less susceptible to antibiotics, while medical researchers continue to develop new antibiotics that can kill them. A similar situation occurs with pesticide resistance in plants and insects. Arms races are not necessarily induced by man; a well-documented example involves the spread of a gene in the butterfly Hypolimnas bolina suppressing male-killing activity by Wolbachia bacteria parasites on the island of Samoa, where the spread of the gene is known to have occurred over a period of just five years [15]

Evolution by Means of Natural Selection

A prerequisite for natural selection to result in adaptive evolution, novel traits and speciation, is the presence of heritable genetic variation that results in fitness differences. Genetic variation is the result of mutations, recombinations and alterations in the karyotype (the number, shape, size and internal arrangement of the chromosomes). Any of these changes might have an effect that is highly advantageous or highly disadvantageous, but large effects are very rare. In the past, most changes in the genetic material were considered neutral or close to neutral because they occurred in noncoding DNA or resulted in a synonymous substitution. However, recent research suggests that many mutations in non-coding DNA do have slight deleterious effects.[16][17] Although both mutation rates and average fitness effects of mutations are dependent on the organism, estimates from data in humans have found that a majority of mutations are slightly deleterious.[18]

The exuberant tail of the peacock is thought to be the result of sexual selection by females. This peacock is an albino; selection against albinos in nature is intense because they are easily spotted by predators or are unsuccessful in competition for mates.

By the definition of fitness, individuals with greater fitness are more likely to contribute offspring to the next generation, while individuals with lesser fitness are more likely to die early or fail to reproduce. As a result, alleles that on average result in greater fitness become more abundant in the next generation, while alleles that in general reduce fitness become rarer. If the selection forces remain the same for many generations, beneficial alleles become more and more abundant, until they dominate the population, while alleles with a lesser fitness disappear. In every generation, new mutations and re-combinations arise spontaneously, producing a new spectrum of phenotypes. Therefore, each new generation will be enriched by the increasing abundance of alleles that contribute to those traits that were favored by selection, enhancing these traits over successive generations.

Some mutations occur in so-called regulatory genes. Changes in these can have large effects on the phenotype of the individual because they regulate the function of many other genes. Most, but not all, mutations in regulatory genes result in non-viable zygotes. Examples of nonlethal regulatory mutations occur in HOX genes in humans, which can result in a cervical rib[19] or polydactyly, an increase in the number of fingers or toes.[20] When such mutations result in a higher fitness, natural selection will favor these phenotypes and the novel trait will spread in the population.

X-ray of the left hand of a ten year old boy with polydactyly.

Established traits are not immutable; traits that have high fitness in one environmental context may be much less fit if environmental conditions change. In the absence of natural selection to preserve such a trait, it will become more variable and deteriorate over time, possibly resulting in a vestigial manifestation of the trait, also called evolutionary baggage. In many circumstances, the apparently vestigial structure may retain a limited functionality, or may be co-opted for other advantageous traits in a phenomenon known as preadaptation. A famous example of a vestigial structure, the eye of the blind mole rat, is believed to retain function in photoperiod perception.[21]


Speciation requires selective mating, which result in a reduced gene flow. Selective mating can be the result of 1. Geographic isolation, 2. Behavioral isolation, or 3. Temporal isolation. For example, a change in the physical environment (geographic isolation by an extrinsic barrier) would follow number 1, a change in camouflage for number 2 or a shift in mating times (i.e., one species of deer shifts location and therefore changes its “rut”) for number 3.[citation needed]

Over time, these subgroups might diverge radically to become different species, either because of differences in selection pressures on the different subgroups, or because different mutations arise spontaneously in the different populations, or because of founder effects – some potentially beneficial alleles may, by chance, be present in only one or other of two subgroups when they first become separated. A lesser-known mechanism of speciation occurs via hybridization, well-documented in plants and occasionally observed in species-rich groups of animals such as cichlid fishes.[22] Such mechanisms of rapid speciation can reflect a mechanism of evolutionary change known as punctuated equilibrium, which suggests that evolutionary change and in particular speciation typically happens quickly after interrupting long periods of stasis.

Genetic changes within groups result in increasing incompatibility between the genomes of the two subgroups, thus reducing gene flow between the groups. Gene flow will effectively cease when the distinctive mutations characterizing each subgroup become fixed. As few as two mutations can result in speciation: if each mutation has a neutral or positive effect on fitness when they occur separately, but a negative effect when they occur together, then fixation of these genes in the respective subgroups will lead to two reproductively isolated populations. According to the biological species concept, these will be two different species.

Historical Development

The modern theory of natural selection derives from the work of Charles Darwin in the nineteenth century.

Pre-Darwinian theories

Several ancient philosophers expressed the idea that nature produces a huge variety of creatures, randomly, and that only those creatures that manage to provide for themselves and reproduce successfully survive; well-known examples include Empedocles[23] and his intellectual successor, the Roman poet Lucretius.[24] Empedocles’ idea that organisms arose entirely by the incidental workings of causes such as heat and cold was criticized by Aristotle in Book II of Physics.[25] He posited natural teleology in its place. He believed that form was achieved for a purpose, citing the regularity of heredity in species as proof.[26][27] Nevertheless, he acceded that new types of animals, monstrosities (τερας), can occur in very rare instances (Generation of Animals, Book IV).[28]

The struggle for existence was later described by Islamic writer Al-Jahiz in the 9th century, who argued that environmental factors influence animals to develop new characteristics to ensure survival.[29][30][31][verification needed] According to Rainow, the 11th century scholar Abu Rayhan Biruni described the idea of artificial selection and argued that nature works in much the same way.[32]

The classical arguments were reintroduced in the 18th century by Pierre Louis Maupertuis[33] and others, including Charles Darwin’s grandfather Erasmus Darwin. While these forerunners had an influence on Darwinism, they later had little influence on the trajectory of evolutionary thought after Charles Darwin.

Until the early 19th century, the prevailing view in Western societies was that differences between individuals of a species were uninteresting departures from their Platonic idealism (or typus) of created kinds. However, the theory of uniformitarianism in geology promoted the idea that simple, weak forces could act continuously over long periods of time to produce radical changes in the Earth’s landscape. The success of this theory raised awareness of the vast scale of geological time and made plausible the idea that tiny, virtually imperceptible changes in successive generations could produce consequences on the scale of differences between species.

Early 19th-century evolutionists such as Jean Baptiste Lamarck suggested the inheritance of acquired characteristics as a mechanism for evolutionary change; adaptive traits acquired by an organism during its lifetime could be inherited by that organism’s progeny, eventually causing transmutation of species.[34] This theory has come to be known as Lamarckism and was an influence on the anti-genetic ideas of the Stalinist Soviet biologist Trofim Lysenko.[35]

Darwin’s theory

In 1859, Charles Darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. He defined natural selection as the “principle by which each slight variation [of a trait], if useful, is preserved”.[36] The concept was simple but powerful: individuals best adapted to their environments are more likely to survive and reproduce. As long as there is some variation between them, there will be an inevitable selection of individuals with the most advantageous variations. If the variations are inherited, then differential reproductive success will lead to a progressive evolution of particular populations of a species, and populations that evolve to be sufficiently different eventually become different species.[37]

Darwin’s ideas were inspired by the observations that he had made on the Beagle voyage, and by the work of a political economist, the Reverend Thomas Malthus, who in An Essay on the Principle of Population, noted that population (if unchecked) increases exponentially, whereas the food supply grows only arithmetically; thus, inevitable limitations of resources would have demographic implications, leading to a “struggle for existence”.[38] When Darwin read Malthus in 1838 he was already primed by his work as a naturalist to appreciate the “struggle for existence” in nature and it struck him that as population outgrew resources, “favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of new species.”[39]

Here is Darwin’s own summary of the idea, which can be found in the fourth chapter of the Origin:

If during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organisation, and I think this cannot be disputed; if there be, owing to the high geometrical powers of increase of each species, at some age, season, or year, a severe struggle for life, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of existence, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, I think it would be a most extraordinary fact if no variation ever had occurred useful to each being’s own welfare, in the same way as so many variations have occurred useful to man. But, if variations useful to any organic being do occur, assuredly individuals thus characterised will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will tend to produce offspring similarly characterised. This principle of preservation, I have called, for the sake of brevity, Natural Selection.

Once he had his theory “by which to work”, Darwin was meticulous about gathering and refining evidence as his “prime hobby” before making his idea public. He was in the process of writing his “big book” to present his researches when the naturalist Alfred Russel Wallace independently conceived of the principle and described it in an essay he sent to Darwin to forward to Charles Lyell. Lyell and Joseph Dalton Hooker decided (without Wallace’s knowledge) to present his essay together with unpublished writings that Darwin had sent to fellow naturalists, and On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection was read to the Linnean Society announcing co-discovery of the principle in July 1858.[40] Darwin published a detailed account of his evidence and conclusions in On the Origin of Species in 1859. In the 3rd edition of 1861 Darwin acknowledged that others — a notable one being William Charles Wells in 1813, and Patrick Matthew in 1831 — had proposed similar ideas, but had neither developed them nor presented them in notable scientific publications.[41]

Darwin thought of natural selection by analogy to how farmers select crops or livestock for breeding, which he called “artificial selection”; in his early manuscripts he referred to a Nature, which would do the selection. At the time, other mechanisms of evolution such as evolution by genetic drift were not yet explicitly formulated, and Darwin believed that selection was likely only part of the story: “I am convinced that [it] has been the main, but not exclusive means of modification.”[42] In a letter to Charles Lyell in September 1860, Darwin regretted the use of the term “Natural Selection”, preferring the term “Natural Preservation”.[43]

For Darwin and his contemporaries, natural selection was in essence synonymous with evolution by natural selection. After the publication of On the Origin of Species, educated people generally accepted that evolution had occurred in some form. However, natural selection remained controversial as a mechanism, partly because it was perceived to be too weak to explain the range of observed characteristics of living organisms, and partly because even supporters of evolution balked at its “unguided” and non-progressive nature,[44] a response that has been characterized as the single most significant impediment to the idea’s acceptance.[45]

However, some thinkers enthusiastically embraced natural selection; after reading Darwin, Herbert Spencer introduced the term survival of the fittest, which became a popular summary of the theory.[46] The fifth edition of On the Origin of Species published in 1869 included Spencer’s phrase as an alternative to natural selection, with credit given: “But the expression often used by Mr. Herbert Spencer, of the Survival of the Fittest, is more accurate, and is sometimes equally convenient.”[47] Although the phrase is still often used by non-biologists, modern biologists avoid it because it is tautological if “fittest” is read to mean “functionally superior” and is applied to individuals rather than considered as an averaged quantity over populations.[48]

Modern evolutionary synthesis

Natural selection relies crucially on the idea of heredity, but it was developed long before the basic concepts of genetics. Although the Austrian monk Gregor Mendel, the father of modern genetics, was a contemporary of Darwin’s, his work would lie in obscurity until the early 20th century. Only after the integration of Darwin’s theory of evolution with a complex statistical appreciation of Gregor Mendel’s ‘re-discovered’ laws of inheritance did natural selection become generally accepted by scientists.

The work of Ronald Fisher (who developed the required mathematical language and The Genetical Theory of Natural Selection),[3] J.B.S. Haldane (who introduced the concept of the “cost” of natural selection),[49] Sewall Wright (who elucidated the nature of selection and adaptation),[50] Theodosius Dobzhansky (who established the idea that mutation, by creating genetic diversity, supplied the raw material for natural selection: see Genetics and the Origin of Species),[51] William Hamilton (who conceived of kin selection), Ernst Mayr (who recognised the key importance of reproductive isolation for speciation: see Systematics and the Origin of Species)[52] and many others formed the modern evolutionary synthesis. This synthesis cemented natural selection as the foundation of evolutionary theory, where it remains today.

Impact of the Idea

Darwin’s ideas, along with those of Adam Smith and Karl Marx, had a profound influence on 19th century thought. Perhaps the most radical claim of the theory of evolution through natural selection is that “elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner” evolved from the simplest forms of life by a few simple principles. This claim inspired some of Darwin’s most ardent supporters—and provoked the most profound opposition. The radicalism of natural selection, according to Stephen Jay Gould,[53] lay in its power to “dethrone some of the deepest and most traditional comforts of Western thought”. In particular, it challenged long-standing beliefs in such concepts as a special and exalted place for humans in the natural world and a benevolent creator whose intentions were reflected in nature’s order and design.

In the words of the philosopher Daniel Dennett,[54] “Darwin’s dangerous idea” of evolution by natural selection is a “universal acid,” which cannot be kept restricted to any vessel or container, as it soon leaks out, working its way into ever-wider surroundings. Thus, in the last decades, the concept of natural selection has spread from evolutionary biology into virtually all disciplines, including evolutionary computation, quantum darwinism, evolutionary economics, evolutionary epistemology, evolutionary psychology, and cosmological natural selection. This unlimited applicability has been called Universal Darwinism.

Cell and molecular biology

In the 19th century, Wilhelm Roux, a founder of modern embryology, wrote a book entitled « Der Kampf der Teile im Organismus » (The struggle of parts in the organism) in which he suggested that the development of an organism results from a Darwinian competition between the parts of the embryo, occurring at all levels, from molecules to organs. In recent years, a modern version of this theory has been proposed by Jean-Jacques Kupiec. According to this cellular Darwinism, stochasticity at the molecular level generates diversity in cell types whereas cell interactions impose a characteristic order on the developing embryo.

Social and psychological theory

The social implications of the theory of evolution by natural selection also became the source of continuing controversy. Friedrich Engels, a German political philosopher and co-originator of the ideology of communism, wrote in 1872 that “Darwin did not know what a bitter satire he wrote on mankind when he showed that free competition, the struggle for existence, which the economists celebrate as the highest historical achievement, is the normal state of the animal kingdom”.[55] Interpretation of natural selection as necessarily ‘progressive’, leading to increasing ‘advances’ in intelligence and civilisation, was used as a justification for colonialism and policies of eugenics, as well as broader sociopolitical positions now described as Social Darwinism. Konrad Lorenz won the Nobel Prize in Physiology or Medicine in 1973 for his analysis of animal behavior in terms of the role of natural selection (particularly group selection). However, in Germany in 1940, in writings that he subsequently disowned, he used the theory as a justification for policies of the Nazi state. He wrote “… selection for toughness, heroism, and social utility…must be accomplished by some human institution, if mankind, in default of selective factors, is not to be ruined by domestication-induced degeneracy. The racial idea as the basis of our state has already accomplished much in this respect.”[56] Others have developed ideas that human societies and culture evolve by mechanisms that are analogous to those that apply to evolution of species.[57]

More recently, work among anthropologists and psychologists has led to the development of sociobiology and later evolutionary psychology, a field that attempts to explain features of human psychology in terms of adaptation to the ancestral environment. The most prominent such example, notably advanced in the early work of Noam Chomsky and later by Steven Pinker, is the hypothesis that the human brain is adapted to acquire the grammatical rules of natural language.[58] Other aspects of human behavior and social structures, from specific cultural norms such as incest avoidance to broader patterns such as gender roles, have been hypothesized to have similar origins as adaptations to the early environment in which modern humans evolved. By analogy to the action of natural selection on genes, the concept of memes – “units of cultural transmission”, or culture’s equivalents of genes undergoing selection and recombination – has arisen, first described in this form by Richard Dawkins[59] and subsequently expanded upon by philosophers such as Daniel Dennett as explanations for complex cultural activities, including human consciousness.[60] Extensions of the theory of natural selection to such a wide range of cultural phenomena have been distinctly controversial and are not widely accepted.[61]

Information and systems theory

In 1922, Alfred Lotka proposed that natural selection might be understood as a physical principle that could be described in terms of the use of energy by a system,[62] a concept that was later developed by Howard Odum as the maximum power principle whereby evolutionary systems with selective advantage maximise the rate of useful energy transformation. Such concepts are sometimes relevant in the study of applied thermodynamics.

The principles of natural selection have inspired a variety of computational techniques, such as “soft” artificial life, that simulate selective processes and can be highly efficient in ‘adapting’ entities to an environment defined by a specified fitness function.[63] For example, a class of heuristic optimization algorithms known as genetic algorithms, pioneered by John Holland in the 1970s and expanded upon by David E. Goldberg,[64] identify optimal solutions by simulated reproduction and mutation of a population of solutions defined by an initial probability distribution.[65] Such algorithms are particularly useful when applied to problems whose solution landscape is very rough or has many local minima.

Genetic Basis of Natural Selection

The idea of natural selection predates the understanding of genetics. We now have a much better idea of the biology underlying heritability, which is the basis of natural selection.

Genotype and phenotype

Natural selection acts on an organism’s phenotype, or physical characteristics. Phenotype is determined by an organism’s genetic make-up (genotype) and the environment in which the organism lives. Often, natural selection acts on specific traits of an individual, and the terms phenotype and genotype are used narrowly to indicate these specific traits.

When different organisms in a population possess different versions of a gene for a certain trait, each of these versions is known as an allele. It is this genetic variation that underlies phenotypic traits. A typical example is that certain combinations of genes for eye color in humans that, for instance, give rise to the phenotype of blue eyes. (On the other hand, when all the organisms in a population share the same allele for a particular trait, and this state is stable over time, the allele is said to be fixed in that population.)

Some traits are governed by only a single gene, but most traits are influenced by the interactions of many genes. A variation in one of the many genes that contributes to a trait may have only a small effect on the phenotype; together, these genes can produce a continuum of possible phenotypic values.[66]

Directionality of selection

When some component of a trait is heritable, selection will alter the frequencies of the different alleles, or variants of the gene that produces the variants of the trait. Selection can be divided into three classes, on the basis of its effect on allele frequencies.[67]

Directional selection occurs when a certain allele has a greater fitness than others, resulting in an increase of its frequency. This process can continue until the allele is fixed and the entire population shares the fitter phenotype. It is directional selection that is illustrated in the antibiotic resistance example above.

Far more common is stabilizing selection (which is commonly confused with purifying selection[68][69]), which lowers the frequency of alleles that have a deleterious effect on the phenotype – that is, produce organisms of lower fitness. This process can continue until the allele is eliminated from the population. Purifying selection results in functional genetic features, such as protein-coding genes or regulatory sequences, being conserved over time due to selective pressure against deleterious variants.

Finally, a number of forms of balancing selection exist, which do not result in fixation, but maintain an allele at intermediate frequencies in a population. This can occur in diploid species (that is, those that have two pairs of chromosomes) when heterozygote individuals, who have different alleles on each chromosome at a single genetic locus, have a higher fitness than homozygote individuals that have two of the same alleles. This is called heterozygote advantage or overdominance, of which the best-known example is the malarial resistance observed in heterozygous humans who carry only one copy of the gene for sickle cell anemia. Maintenance of allelic variation can also occur through disruptive or diversifying selection, which favors genotypes that depart from the average in either direction (that is, the opposite of overdominance), and can result in a bimodal distribution of trait values. Finally, balancing selection can occur through frequency-dependent selection, where the fitness of one particular phenotype depends on the distribution of other phenotypes in the population. The principles of game theory have been applied to understand the fitness distributions in these situations, particularly in the study of kin selection and the evolution of reciprocal altruism.[70][71]

Selection and genetic variation

A portion of all genetic variation is functionally neutral in that it produces no phenotypic effect or significant difference in fitness; the hypothesis that this variation accounts for a large fraction of observed genetic diversity is known as the neutral theory of molecular evolution and was originated by Motoo Kimura. When genetic variation does not result in differences in fitness, selection cannot directly affect the frequency of such variation. As a result, the genetic variation at those sites will be higher than at sites where variation does influence fitness.[67] However, after a period with no new mutation, the genetic variation at these sites will be eliminated due to genetic drift.

Mutation selection balance

Natural selection results in the reduction of genetic variation through the elimination of maladapted individuals and consequently of the mutations that caused the maladaptation. At the same time, new mutations occur, resulting in a mutation-selection balance. The exact outcome of the two processes depends both on the rate at which new mutations occur and on the strength of the natural selection, which is a function of how unfavorable the mutation proves to be. Consequently, changes in the mutation rate or the selection pressure will result in a different mutation-selection balance.

Genetic linkage

Genetic linkage occurs when the loci of two alleles are linked, or in close proximity to each other on the chromosome. During the formation of gametes, recombination of the genetic material results in reshuffling of the alleles. However, the chance that such a reshuffle occurs between two alleles depends on the distance between those alleles; the closer the alleles are to each other, the less likely it is that such a reshuffle will occur. Consequently, when selection targets one allele, this automatically results in selection of the other allele as well; through this mechanism, selection can have a strong influence on patterns of variation in the genome.

Selective sweeps occur when an allele becomes more common in a population as a result of positive selection. As the prevalence of one allele increases, linked alleles can also become more common, whether they are neutral or even slightly deleterious. This is called genetic hitchhiking. A strong selective sweep results in a region of the genome where the positively selected haplotype (the allele and its neighbors) are in essence the only ones that exist in the population.

Whether a selective sweep has occurred or not can be investigated by measuring linkage disequilibrium, or whether a given haplotype is overrepresented in the population. Normally, genetic recombination results in a reshuffling of the different alleles within a haplotype, and none of the haplotypes will dominate the population. However, during a selective sweep, selection for a specific allele will also result in selection of neighboring alleles. Therefore, the presence of a block of strong linkage disequilibrium might indicate that there has been a ‘recent’ selective sweep near the center of the block, and this can be used to identify sites recently under selection.

Background selection is the opposite of a selective sweep. If a specific site experiences strong and persistent purifying selection, linked variation will tend to be weeded out along with it, producing a region in the genome of low overall variability. Because background selection is a result of deleterious new mutations, which can occur randomly in any haplotype, it does not produce clear blocks of linkage disequilibrium, although with low recombination it can still lead to slightly negative linkage disequilibrium overall.[72]


1.       ^ a b Darwin C (1859) On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life John Murray, London; modern reprint Charles Darwin, Julian Huxley (2003). On The Origin of Species. Signet Classics. ISBN 0-451-52906-5. Published online at The complete work of Charles Darwin online: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life.

2.       ^ Ken Miller (August, 1999). “The Peppered Moth”. Retrieved 2011-04-13.

3.       ^ a b Fisher RA (1930) The Genetical Theory of Natural Selection Clarendon Press, Oxford

4.       ^ Works employing or describing this usage:
Endler JA (1986). Natural Selection in the Wild. Princeton, New Jersey: Princeton University Press. ISBN 0-691-00057-3.
Williams GC (1966). Adaptation and Natural Selection. Oxford University Press.

5.       ^ Works employing or describing this usage:
Lande R & Arnold SJ (1983) The measurement of selection on correlated characters. Evolution 37:1210-26
Futuyma DJ (2005) Evolution. Sinauer Associates, Inc., Sunderland, Massachusetts. ISBN 0-87893-187-2
Haldane, J.B.S. 1953. The measurement of natural selection. Proceedings of the 9th International Congress of Genetics. 1: 480-487

6.       ^ Sober E (1984; 1993) The Nature of Selection: Evolutionary Theory in Philosophical Focus University of Chicago Press ISBN 0-226-76748-5

7.       ^

8.       ^ Modified from Christiansen FB (1984) The definition and measurement of fitness. In: Evolutionary ecology (ed. Shorrocks B) pp65–79. Blackwell Scientific, Oxford by adding survival selection in the reproductive phase

9.       ^ Pitnick S & Markow TA (1994) Large-male advantage associated with the costs of sperm production in Drosophila hydei, a species with giant sperm. Proc Natl Acad Sci USA 91:9277-81; Pitnick S (1996) Investment in testes and the cost of making long sperm in Drosophila. Am Nat 148:57-80

10.    ^ Andersson, M (1995). Sexual Selection. Princeton, New Jersey: Princeton University Press. ISBN 0-691-00057-3.

11.    ^ Eens, M; Pinxten, R. (2000). “Sex-role reversal in vertebrates: behavioural and endocrinological accounts”. Behav Processes 51 (1–3): 135–147. doi:10.1016/S0376-6357(00)00124-8. PMID 11074317.

12.    ^ Barlow, GW. (2005). “How Do We Decide that a Species is Sex-Role Reversed?”. The Quarterly Review of Biology 80 (1): 28–35. doi:10.1086/431022. PMID 15884733.

13.    ^ “MRSA Superbug News”. Retrieved 2006-05-06.

14.    ^ Schito GC (2006). “The importance of the development of antibiotic resistance in Staphylococcus aureus“. Clin Microbiol Infect 12 Suppl 1: 3–8. doi:10.1111/j.1469-0691.2006.01343.x. PMID 16445718. [1]

15.    ^ Sylvain Charlat, Emily A. Hornett, James H. Fullard, Neil Davies, George K. Roderick, Nina Wedell & Gregory D. D. Hurst (2007). “Extraordinary flux in sex ratio”. Science 317 (5835): 214. doi:10.1126/science.1143369. PMID 17626876.

16.    ^ Kryukov, GV; Schmidt, S; Sunyaev, S (2005). “Small fitness effect of mutations in highly conserved non-coding regions”. Human Molecular Genetics 14 (15): 2221–9. doi:10.1093/hmg/ddi226. PMID 15994173.

17.    ^ Bejerano G, Pheasant M, Makunin I, Stephen S, Kent WJ, Mattick JS & Haussler D (2004) Ultraconserved elements in the human genome. Science 304:1321-5

18.    ^ Eyre-Walker, A; Woolfit, M; Phelps, T. (2006). “The distribution of fitness effects of new deleterious amino acid mutations in humans”. Genetics 173 (2): 891–900. doi:10.1534/genetics.106.057570. PMC 1526495. PMID 16547091.

19.    ^ Galis, F (1999). “Why do almost all mammals have seven cervical vertebrae? developmental constraints, Hox genes, and cancer”. J Exp Zool 285 (1): 19–26. doi:10.1002/(SICI)1097-010X(19990415)285:1<19::AID-JEZ3>3.0.CO;2-Z. PMID 10327647.

20.    ^ Zakany J, FromentalRamain C, Warot X & Duboule D (1997) Regulation of number and size of digits by posterior Hox genes: a dose-dependent mechanism with potential evolutionary implications. Proc Natl Acad Sci USA 94:13695-700

21.    ^ Sanyal, S; Jansen, HG; de Grip, WJ; Nevo, E; de Jong, WW. (1990). “The eye of the blind mole rat, Spalax ehrenbergi. Rudiment with hidden function?”. Invest Ophthalmol Vis Sci. 31 (7): 1398–404. PMID 2142147.

22.    ^ Salzburger, W; Baric, S; Sturmbauer, C. (2002). “Speciation via introgressive hybridization in East African cichlids?”. Mol Ecol 11 (3): 619–625. doi:10.1046/j.0962-1083.2001.01438.x. PMID 11918795.

23.    ^ Empedocles. On Nature. Book II.

24.    ^ Lucretius. De rerum natura. Book V.

25.    ^ Aristotle. Physics. Book II, Chapters 4 and 8.

26.    ^ Jonathan Lear (1988). Aristotle: the desire to understand. Cambridge University Press. p. 38. ISBN 9780521347624.

27.    ^ Devin Henry (2006). “Aristotle on the Mechanism of Inheritance”. Journal of the History of Biology (Springer) 39: 425–455. doi:10.1007/s10739-005-3058-y.

28.    ^ André Ariew (2007). “Platonic and Aristotelian Roots of Teleological Arguments in Cosmology and Biology”. In David L. Hull & Michael Ruse. The Cambridge Companion to the Philosophy of Biology. Cambridge University Press.. ISBN 9780521616713.

29.    ^ Zirkle, Conway (1941). “Natural Selection before the “Origin of Species”. Proceedings of the American Philosophical Society 84 (1): 71–123.

30.    ^ Mehmet Bayrakdar (Third Quarter, 1983). “Al-Jahiz And the Rise of Biological Evolutionism”, The Islamic Quarterly. London.

31.    ^ Paul S. Agutter & Denys N. Wheatley (2008). Thinking about Life: The History and Philosophy of Biology and Other Sciences. Springer. p. 43. ISBN 1402088655

32.    ^ Jan Z. Wilczynski (December 1959). “On the Presumed Darwinism of Alberuni Eight Hundred Years before Darwin”. Isis 50 (4): 459–466. doi:10.1086/348801

33.    ^ Maupertuis, Pierre Louis (1748). “Derivation of the laws of motion and equilibrium from a metaphysical principle (Original French text)”. Histoire de l’academie des sciences et belle lettres de Berlin 1746: 267–294.

34.    ^ Chevalier de Lamarck J-B, de Monet PA (1809) Philosophie Zoologique

35.    ^ Joravsky, D. (1959). “Soviet Marxism and Biology before Lysenko”. Journal of the History of Ideas 20 (1): 85–104. doi:10.2307/2707968.

36.    ^ Darwin 1859, p. 61

37.    ^ Darwin 1859, p. 5

38.    ^ T. Robert Malthus (1798). “An Essay on the Principle of Population”. Rogers State University. Retrieved 2008-11-03.

39.    ^ Charles Darwin; ed. Nora Barlow (1958). “The autobiography of Charles Darwin 1809-1882”. London: Collins. pp. 120. Retrieved 2008-11-03.

40.    ^ Wallace, Alfred Russel (1870) Contributions to the Theory of Natural Selection New York: Macmillan & Co. [2]

41.    ^ Darwin 1861, p. xiii

42.    ^ Darwin 1859, p. 6

43.    ^ “Darwin Correspondence Online Database: Darwin, C. R. to Lyell, Charles, 28 September 1860”. Retrieved 2006-05-10.

44.    ^ Eisley L. (1958). Darwin’s Century: Evolution and the Men Who Discovered It. Doubleday & Co: New York, USA.

45.    ^ Kuhn TS. [1962] (1996). The Structure of Scientific Revolution 3rd ed. University of Chicago Press: Chicago, Illinois, USA. ISBN 0-226-45808-3

46.    ^ “Letter 5145 — Darwin, C. R. to Wallace, A. R., 5 July (1866)”. Darwin Correspondence Project. Retrieved 2010-01-12.
Maurice E. Stucke. “Better Competition Advocacy”. Retrieved 2007-08-29. “Herbert Spencer in his Principles of Biology of 1864, vol. 1, p. 444, wrote “This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called ‘natural selection’, or the preservation of favoured races in the struggle for life.””

47.    ^ Darwin 1872, p. 49.

48.    ^ Mills SK, Beatty JH. [1979] (1994). The Propensity Interpretation of Fitness. Originally in Philosophy of Science (1979) 46: 263-286; republished in Conceptual Issues in Evolutionary Biology 2nd ed. Elliott Sober, ed. MIT Press: Cambridge, Massachusetts, USA. pp3-23. ISBN 0-262-69162-0.

49.    ^ Haldane JBS (1932) The Causes of Evolution; Haldane JBS (1957) The cost of natural selection. J Genet 55:511-24([3].

50.    ^ Wright, S (1932). “The roles of mutation, inbreeding, crossbreeding and selection in evolution”. Proc 6th Int Cong Genet 1: 356–66.

51.    ^ Dobzhansky Th (1937) Genetics and the Origin of Species Columbia University Press, New York. (2nd ed., 1941; 3rd edn., 1951)

52.    ^ Mayr E (1942) Systematics and the Origin of Species Columbia University Press, New York. ISBN 0-674-86250-3

53.    ^ The New York Review of Books: Darwinian Fundamentalism (accessed May 6, 2006)

54.    ^ Dennett, D. C. (1995). Darwin’s dangerous idea: evolution and the meanings of life. Simon & Schuster.

55.    ^ Engels F (1873-86) Dialectics of Nature 3d ed. Moscow: Progress, 1964 [4]

56.    ^ Quoted in translation in Eisenberg L (2005) Which image for Lorenz? Am J Psychiatry 162:1760 [5]

57.    ^ e.g. Wilson, DS (2002) Darwin’s Cathedral: Evolution, Religion, and the Nature of Society. University of Chicago Press, ISBN 0-226-90134-3

58.    ^ Pinker S. [1994] (1995). The Language Instinct: How the Mind Creates Language. HarperCollins: New York, NY, USA. ISBN 0-06-097651-9

59.    ^ Dawkins R. [1976] (1989). The Selfish Gene. Oxford University Press: New York, NY, USA, p.192. ISBN 0-19-286092-5

60.    ^ Dennett DC. (1991). Consciousness Explained. Little, Brown, and Co: New York, NY, USA. ISBN 0-316-18066-1

61.    ^ For example, see Rose H, Rose SPR, Jencks C. (2000). Alas, Poor Darwin: Arguments Against Evolutionary Psychology. Harmony Books. ISBN 0-609-60513-5

62.    ^ Lotka AJ (1922a) Contribution to the energetics of evolution [PDF] Proc Natl Acad Sci USA 8:147–51
Lotka AJ (1922b) Natural selection as a physical principle [PDF] Proc Natl Acad Sci USA 8:151–4

63.    ^ Kauffman SA (1993) The Origin of order. Self-organization and selection in evolution. New York: Oxford University Press ISBN 0-19-507951-5

64.    ^ Goldberg DE. (1989). Genetic Algorithms in Search, Optimization and Machine Learning. Addison-Wesley: Boston, MA, USA

65.    ^ Mitchell, Melanie, (1996), An Introduction to Genetic Algorithms, MIT Press, Cambridge, MA.

66.    ^ Falconer DS & Mackay TFC (1996) Introduction to Quantitative Genetics Addison Wesley Longman, Harlow, Essex, UK ISBN 0-582-24302-5

67.    ^ a b Rice SH. (2004). Evolutionary Theory: Mathematical and Conceptual Foundations. Sinauer Associates: Sunderland, Massachusetts, USA. ISBN 0-87893-702-1 See esp. ch. 5 and 6 for a quantitative treatment.

68.    ^ Lemey, Philippe; Marco Salemi, Anne-Mieke Vandamme (2009). The Phylogenetic Handbook. Cambridge University Press. ISBN 978-0-521-73071.

69.    ^

70.    ^ Hamilton, WD (1964). “The genetical evolution of social behaviour. II”. Journal of theoretical biology 7 (1): 17–52. doi:10.1016/0022-5193(64)90039-6. PMID 5875340.

71.    ^ Trivers, RL. (1971). “The evolution of reciprocal altruism”. Q Rev Biol 46: 35–57. doi:10.1086/406755.

72.    ^ Keightley PD. and Otto SP (2006). “Interference among deleterious mutations favours sex and recombination in finite populations”. Nature 443 (7107): 89–92. doi:10.1038/nature05049. PMID 16957730.

Modern Evolutionary Synthesis

The modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution. It is also referred to as the new synthesis, the modern synthesis, the evolutionary synthesis, millennium synthesis and the neo-Darwinian synthesis.

The synthesis, produced between 1936 and 1947, reflects the current consensus.[1] The previous development of population genetics, between 1918 and 1932, was a stimulus, as it showed that Mendelian genetics was consistent with natural selection and gradual evolution. The synthesis is still, to a large extent, the current paradigm in evolutionary biology.[2]

The modern synthesis solved difficulties and confusions caused by the specialisation and poor communication between biologists in the early years of the 20th century. At its heart was the question of whether Mendelian genetics could be reconciled with gradual evolution by means of natural selection. A second issue was whether the broad-scale changes (macroevolution) seen by palaeontologists could be explained by changes seen in local populations (microevolution).

The synthesis included evidence from biologists, trained in genetics, who studied populations in the field and in the laboratory. These studies were crucial to evolutionary theory. The synthesis drew together ideas from several branches of biology which had become separated, particularly genetics, cytology, systematics, botany, morphology, ecology and paleontology.

Julian Huxley invented the term, when he produced his book, Evolution: The Modern Synthesis (1942). Other major figures in the modern synthesis include R. A. Fisher, Theodosius Dobzhansky, J. B. S. Haldane, Sewall Wright, E. B. Ford, Ernst Mayr, Bernhard Rensch, Sergei Chetverikov, George Gaylord Simpson, and G. Ledyard Stebbins.

Summary of the Modern Synthesis

The modern synthesis bridged the gap between experimental geneticists and naturalists, and between palaeontologists. It states that:[3][4][5]

  1. All evolutionary phenomena can be explained in a way consistent with known genetic mechanisms and the observational evidence of naturalists.
  2. Evolution is gradual: small genetic changes regulated by natural selection accumulate over long periods. Discontinuities amongst species (or other taxa) are explained as originating gradually through geographical separation and extinction (not saltation).
  3. Natural selection is by far the main mechanism of change; even slight advantages are important when continued. The object of selection is the phenotype in its surrounding environment.
  4. The role of genetic drift is equivocal. Though strongly supported initially by Dobzhansky, it was downgraded later as results from ecological genetics were obtained.
  5. Thinking in terms of populations, rather than individuals, is primary: the genetic diversity existing in natural populations is a key factor in evolution. The strength of natural selection in the wild is greater than previously expected; the effect of ecological factors such as niche occupation and the significance of barriers to gene flow are all important.
  6. In palaeontology, the ability to explain historical observations by extrapolation from microevolution to macroevolution is proposed. Historical contingency means explanations at different levels may exist. Gradualism does not mean constant rate of change.

The idea that speciation occurs after populations are reproductively isolated has been much debated. In plants, polyploidy must be included in any view of speciation. Formulations such as ‘evolution consists primarily of changes in the frequencies of alleles between one generation and another’ were proposed rather later. The traditional view is that developmental biology (‘evo-devo‘) played little part in the synthesis,[6] but an account of Gavin de Beer‘s work by Stephen J. Gould suggests he may be an exception.[7]

Developments Leading up to the Synthesis


Charles Darwin‘s On the Origin of Species was successful in convincing most biologists that evolution had occurred, but was less successful in convincing them that natural selection was its primary mechanism. In the 19th and early 20th centuries, variations of Lamarckism, orthogenesis (‘progressive’ evolution), and saltationism (evolution by jumps) were discussed as alternatives.[8] Also, Darwin did not offer a precise explanation of how new species arise. As part of the disagreement about whether natural selection alone was sufficient to explain speciation, George Romanes coined the term neo-Darwinism to refer to the version of evolution advocated by Alfred Russel Wallace and August Weismann with its heavy dependence on natural selection.[9] Weismann and Wallace rejected the Lamarckian idea of inheritance of acquired characteristics, something that Darwin had not ruled out.[10]

Weismann’s idea was that the relationship between the hereditary material, which he called the germ plasm (German, Keimplasma), and the rest of the body (the soma) was a one-way relationship: the germ-plasm formed the body, but the body did not influence the germ-plasm, except indirectly in its participation in a population subject to natural selection. Weismann was translated into English, and though he was influential, it took many years for the full significance of his work to be appreciated.[11] Later, after the completion of the modern synthesis, the term neo-Darwinism came to be associated with its core concept: evolution, driven by natural selection acting on variation produced by genetic mutation, and genetic recombination (chromosomal crossovers).[9]


Gregor Mendel‘s work was re-discovered by Hugo de Vries and Carl Correns in 1900. News of this reached William Bateson in England, who reported on the paper during a presentation to the Royal Horticultural Society in May 1900.[12] It showed that the contributions of each parent retained their integrity rather than blending with the contribution of the other parent. This reinforced a division of thought, which was already present in the 1890s.[13] The two schools were:


  • Saltationism (large mutations or jumps), favored by early Mendelians who viewed hard inheritance as incompatible with natural selection[14]
  • Biometric school: led by Karl Pearson and Walter Weldon, argued vigorously against it, saying that empirical evidence indicated that variation was continuous in most organisms, not discrete as Mendelism predicted.


The relevance of Mendelism to evolution was unclear and hotly debated, especially by Bateson, who opposed the biometric ideas of his former teacher Weldon. Many scientists believed the two theories substantially contradicted each other.[15] This debate between the biometricians and the Mendelians continued for some 20 years and was only solved by the development of population genetics.

T. H. Morgan began his career in genetics as a saltationist, and started out trying to demonstrate that mutations could produce new species in fruit flies. However, the experimental work at his lab with Drosophila melanogaster, which helped establish the link between Mendelian genetics and the chromosomal theory of inheritance, demonstrated that rather than creating new species in a single step, mutations increased the genetic variation in the population.[16]

The foundation of population genetics

The first step towards the synthesis was the development of population genetics. R.A. Fisher, J.B.S. Haldane, and Sewall Wright provided critical contributions. In 1918, Fisher produced the paper “The Correlation Between Relatives on the Supposition of Mendelian Inheritance“,[17] which showed how the continuous variation measured by the biometricians could be the result of the action of many discrete genetic loci. In this and subsequent papers culminating in his 1930 book The Genetical Theory of Natural Selection, Fisher was able to show how Mendelian genetics was, contrary to the thinking of many early geneticists, completely consistent with the idea of evolution driven by natural selection.[18] During the 1920s, a series of papers by J.B.S. Haldane applied mathematical analysis to real world examples of natural selection such as the evolution of industrial melanism in peppered moths.[18] Haldane established that natural selection could work in the real world at a faster rate than even Fisher had assumed.[19]

Sewall Wright focused on combinations of genes that interacted as complexes, and the effects of inbreeding on small relatively isolated populations, which could exhibit genetic drift. In a 1932 paper he introduced the concept of an adaptive landscape in which phenomena such as cross breeding and genetic drift in small populations could push them away from adaptive peaks, which would in turn allow natural selection to push them towards new adaptive peaks.[18] Wright’s model would appeal to field naturalists such as Theodosius Dobzhansky and Ernst Mayr who were becoming aware of the importance of geographical isolation in real world populations.[19] The work of Fisher, Haldane and Wright founded the discipline of population genetics. This is the precursor of the modern synthesis, which is an even broader coalition of ideas.[18][19][20] One limitation of the modern synthesis version of population genetics is that it treats one gene locus at a time, neglecting genetic linkage and resulting linkage disequilibrium between loci.

The Modern Synthesis

Theodosius Dobzhansky, a Ukrainian emigrant, who had been a postdoctoral worker in Morgan’s fruit fly lab, was one of the first to apply genetics to natural populations. He worked mostly with Drosophila pseudoobscura. He says pointedly: “Russia has a variety of climates from the Arctic to sub-tropical… Exclusively laboratory workers who neither possess nor wish to have any knowledge of living beings in nature were and are in a minority.”[21] Not surprisingly, there were other Russian geneticists with similar ideas, though for some time their work was known to only a few in the West. His 1937 work Genetics and the Origin of Species was a key step in bridging the gap between population geneticists and field naturalists. It presented the conclusions reached by Fisher, Haldane, and especially Wright in their highly mathematical papers in a form that was easily accessible to others. It also emphasized that real world populations had far more genetic variability than the early population geneticists had assumed in their models, and that genetically distinct sub-populations were important. Dobzhansky argued that natural selection worked to maintain genetic diversity as well as driving change. Dobzhansky had been influenced by his exposure in the 1920s to the work of a Russian geneticist named Sergei Chetverikov who had looked at the role of recessive genes in maintaining a reservoir of genetic variability in a population before his work was shut down by the rise of Lysenkoism in the Soviet Union.[18][19]

Edmund Brisco Ford‘s work complemented that of Dobzhansky. It was as a result of Ford’s work, as well as his own, that Dobzhansky changed the emphasis in the third edition of his famous text from drift to selection.[22] Ford was an experimental naturalist who wanted to test natural selection in nature. He virtually invented the field of research known as ecological genetics. His work on natural selection in wild populations of butterflies and moths was the first to show that predictions made by R.A. Fisher were correct. He was the first to describe and define genetic polymorphism, and to predict that human blood group polymorphisms might be maintained in the population by providing some protection against disease.[23]

Ernst Mayr‘s key contribution to the synthesis was Systematics and the Origin of Species, published in 1942. Mayr emphasized the importance of allopatric speciation, where geographically isolated sub-populations diverge so far that reproductive isolation occurs. He was skeptical of the reality of sympatric speciation believing that geographical isolation was a prerequisite for building up intrinsic (reproductive) isolating mechanisms. Mayr also introduced the biological species concept that defined a species as a group of interbreeding or potentially interbreeding populations that were reproductively isolated from all other populations.[18][19][24] Before he left Germany for the United States in 1930, Mayr had been influenced by the work of German biologist Bernhard Rensch. In the 1920s Rensch, who like Mayr did field work in Indonesia, analyzed the geographic distribution of polytypic species and complexes of closely related species paying particular attention to how variations between different populations correlated with local environmental factors such as differences in climate. In 1947, Rensch published Neuere Probleme der Abstammungslehre: die Transspezifische Evolution (English translation 1959: Evolution above the Species level). This looked at how the same evolutionary mechanisms involved in speciation might be extended to explain the origins of the differences between the higher level taxa. His writings contributed to the rapid acceptance of the synthesis in Germany.[25][26]

George Gaylord Simpson was responsible for showing that the modern synthesis was compatible with paleontology in his book Tempo and Mode in Evolution published in 1944. Simpson’s work was crucial because so many paleontologists had disagreed, in some cases vigorously, with the idea that natural selection was the main mechanism of evolution. It showed that the trends of linear progression (in for example the evolution of the horse) that earlier paleontologists had used as support for neo-Lamarckism and orthogenesis did not hold up under careful examination. Instead the fossil record was consistent with the irregular, branching, and non-directional pattern predicted by the modern synthesis.[18][19]

The botanist G. Ledyard Stebbins was another major contributor to the synthesis. His major work, Variation and Evolution in Plants, was published in 1950. It extended the synthesis to encompass botany including the important effects of hybridization and polyploidy in some kinds of plants.[18]

Further Advances

The modern evolutionary synthesis continued to be developed and refined after the initial establishment in the 1930s and 1940s. The work of W. D. Hamilton, George C. Williams, John Maynard Smith and others led to the development of a gene-centered view of evolution in the 1960s. The synthesis as it exists now has extended the scope of the Darwinian idea of natural selection to include subsequent scientific discoveries and concepts unknown to Darwin, such as DNA and genetics, which allow rigorous, in many cases mathematical, analyses of phenomena such as kin selection, altruism, and speciation.

In The Selfish Gene, author Richard Dawkins asserts the gene is the only true unit of selection.[27] (Dawkins also attempts to apply evolutionary theory to non-biological entities, such as cultural memes, imagined to be subject to selective forces analogous to those affecting biological entities.)

Others, such as Stephen Jay Gould, reject the notion that genetic entities are subject to anything other than genetic or chemical forces, (as well as the idea evolution acts on “populations” per se), reasserting the centrality of the individual organism as the true unit of selection, whose specific phenotype is directly subject to evolutionary pressures.

In 1972, the notion of gradualism in evolution was challenged by a theory of “punctuated equilibrium” put forward by Gould and Niles Eldredge, proposing evolutionary changes could occur in relatively rapid spurts, when selective pressures were heightened, punctuating long periods of morphological stability, as well-adapted organisms coped successfully in their respective environments.

Discovery in the 1980s of Hox genes and regulators conserved across multiple phyletic divisions began the process of addressing basic theoretical problems relating to gradualism, incremental change, and sources of novelty in evolution. Suddenly, evolutionary theorists could answer the charge that spontaneous random mutations should result overwhelmingly in deleterious changes to a fragile, monolithic genome: Mutations in homeobox regulation could safely—yet dramatically—alter morphology at a high level, without damaging coding for specific organs or tissues.

This, in turn, provided the means to model hypothetical genomic changes expressed in the phenotypes of long-extinct species, like the recently discovered “fish with hands”‘ Tiktaalik.

As these recent discoveries suggest, the synthesis continues to undergo regular review, drawing on insights offered by both new biotechnologies and new paleontological discoveries.[28] (See also Current research in evolutionary biology).

After the Synthesis” >

The structure of evolutionary biology.

The history and causes of evolution (center) are subject to various subdisciplines of evolutionary biology. The areas of segments give an impression of the contributions of subdisciplines to the literature of evolutionary biology.

There are a number of discoveries in earth sciences and biology which have arisen since the synthesis. Listed here are some of those topics which are relevant to the evolutionary synthesis, and which seem soundly based.

Understanding of Earth history

The Earth is the stage on which the evolutionary play is performed. Darwin studied evolution in the context of Charles Lyell‘s geology, but our present understanding of Earth history includes some critical advances made during the last half-century.


  • The age of the Earth has been revised upwards. It is now estimated at 4.56 billion years, about one-third of the age of the universe. The Phanerozoic (current eon) only occupies the last one-ninth of this period of time.[29]
  • The triumph of Alfred Wegener‘s idea of continental drift came around 1960. The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which ride on the fluid-like (visco-elastic solid) asthenosphere. This discovery provides a unifying theory for geology, linking phenomena such as volcanos, earthquakes, orogeny, and providing data for many paleogeographical questions.[30] One major question is still unclear: when did plate tectonics begin?[31]
  • Our understanding of the evolution of the atmosphere of Earth has progressed. The substitution of oxygen for carbon dioxide in the atmosphere, which occurred in the Proterozoic, caused probably by cyanobacteria in the form of stromatolites, caused changes leading to the evolution of aerobic organisms.[32][33]
  • The identification of the first generally accepted fossils of microbial life was made by geologists. These rocks have been dated as about 3.465 billion years ago.[34] Walcott was the first geologist to identify pre-Cambrian fossil bacteria from microscopic examination of thin rock slices. He also thought stromatolites were organic in origin. His ideas were not accepted at the time, but may now be appreciated as great discoveries.[35]
  • Information about paleoclimates is increasingly available, and being used in paleontology. One example: the discovery of massive ice ages in the Proterozoic, following the great reduction of CO2 in the atmosphere. These ice ages were immensely long, and led to a crash in microflora.[36] See also Cryogenian period and Snowball Earth.
  • Catastrophism and mass extinctions. A partial reintegration of catastrophism has occurred,[37] and the importance of mass extinctions in large-scale evolution is now apparent. Extinction events disturb relationships between many forms of life and may remove dominant forms and release a flow of adaptive radiation amongst groups that remain. Causes include meteorite strikes (K–T junction; Upper Devonian); flood basalt provinces (Deccan Traps at K/T junction; Siberian Traps at P–T junction); and other less dramatic processes.[38][39]


Conclusion: Our present knowledge of earth history strongly suggests that large-scale geophysical events influenced macroevolution and megaevolution. These terms refer to evolution above the species level, including such events as mass extinctions, adaptive radiation, and the major transitions in evolution.[40][41]

Symbiotic origin of eukaryotic cell structures

Once symbiosis was discovered in lichen and in plant roots (rhizobia in root nodules) in the 19th century, the idea arose that the process might have occurred more widely, and might be important in evolution. Anton de Bary invented the concept of symbiosis;[42] several Russian biologists promoted the idea;[43] Edwin Wilson mentioned it in his text The Cell;[44] as did Ivan Emmanuel Wallin in his Symbionticism and the origin of species;[45] and there was a brief mention by Julian Huxley in 1930;[46] all in vain because sufficient evidence was lacking. Symbiosis as a major evolutionary force was not discussed at all in the evolutionary synthesis.[47]

The role of symbiosis in cell evolution was revived partly by Joshua Lederberg,[48] and finally brought to light by Lynn Margulis in a series of papers and books.[49][50] Some organelles are recognized as being of microbial origin: mitochondria and chloroplasts definitely, cilia, flagella and centrioles possibly, and perhaps the nuclear membrane and much of the chromosome structure as well. What is now clear is that the evolution of eukaryote cells is either caused by, or at least profoundly influenced by, symbiosis with bacterial and archaean cells in the Proterozoic.

The origin of the eukaryote cell by symbiosis in several stages was not part of the evolutionary synthesis. It is, at least on first sight, an example of megaevolution by big jumps. However, what symbiosis provided was a copious supply of heritable variation from microorganisms, which was fine-tuned over a long period to produce the cell structure we see today. This part of the process is consistent with evolution by natural selection.[51]

Trees of life

The ability to analyse sequence in macromolecules (protein, DNA, RNA) provides evidence of descent, and permits us to work out genealogical trees covering the whole of life, since now there are data on every major group of living organisms. This project, begun in a tentative way in the 1960s, has become a search for the universal tree or the universal ancestor, a phrase of Carl Woese.[52][53] The tree that results has some unusual features, especially in its roots. There are two domains of prokaryotes: bacteria and archaea, both of which contributed genetic material to the eukaryotes, mainly by means of symbiosis. Also, since bacteria can pass genetic material to other bacteria, their relationships look more like a web than a tree. Once eukaryotes were established, their sexual reproduction produced the traditional branching tree-like pattern, the only diagram Darwin put in the Origin. The last universal ancestor (LUA) would be a prokaryotic cell before the split between the bacteria and archaea. LUA is defined as most recent organism from which all organisms now living on Earth descend (some 3.5 to 3.8 billion years ago, in the Archean era).[54]

This technique may be used to clarify relationships within any group of related organisms. It is now a standard procedure, and examples are published regularly. April 2009 sees the publication of a tree covering all the animal phyla, derived from sequences from 150 genes in 77 taxa.[55]

Early attempts to identify relationships between major groups were made in the 19th century by Ernst Haeckel, and by comparative anatomists such as Thomas Henry Huxley and E. Ray Lankester. Enthusiasm waned: it was often difficult to find evidence to adjudicate between different opinions. Perhaps for that reason, the evolutionary synthesis paid surprisingly little attention to this activity. It is certainly a lively field of research today.

Evolutionary developmental biology

What once was called embryology played a modest role in the evolutionary synthesis,[56] mostly about evolution by changes in developmental timing (allometry and heterochrony).[57] Man himself was, according to Bolk, a typical case of evolution by retention of juvenile characteristics (neoteny). He listed many characters where “Man, in his bodily development, is a primate foetus that has become sexually mature.”[58] Unfortunately, his interpretation of these ideas was non-Darwinian, but his list of characters is both interesting and convincing.[59]

Evolutionary developmental biology (evo-devo) springs from clear proof that development is closely controlled by special genetic systems, and the hope that comparison of these systems will tell us much about the evolutionary history of different groups.[60][61] In a series of experiments with the fruit-fly Drosophila, Edward B. Lewis was able to identify a complex of genes whose proteins bind to the cis-regulatory regions of target genes. The latter then activate or repress systems of cellular processes that accomplish the final development of the organism.[62][63] Furthermore, the sequence of these control genes show co-linearity: the order of the loci in the chromosome parallels the order in which the loci are expressed along the anterior-posterior axis of the body. Not only that, but this cluster of master control genes programs the development of all higher organisms.[64][65] Each of the genes contains a homeobox, a remarkably conserved DNA sequence. This suggests the complex itself arose by gene duplication.[66][67][68] In his Nobel lecture, Lewis said “Ultimately, comparisons of the [control complexes] throughout the animal kingdom should provide a picture of how the organisms, as well as the [control genes] have evolved.”

The term deep homology was coined to describe the common origin of genetic regulatory apparatus used to build morphologically and phylogenetically disparate animal features.[69] It applies when a complex genetic regulatory system is inherited from a common ancestor, as it is in the evolution of vertebrate and invertebrate eyes. The phenomenon is implicated in many cases of parallel evolution.[70]

A great deal of evolution may take place by changes in the control of development. This may be relevant to punctuated equilibrium theory, for in development a few changes to the control system could make a significant difference to the adult organism. An example is the giant panda, whose place in the Carnivora was long uncertain.[71] Apparently, the giant panda’s evolution required the change of only a few genetic messages (5 or 6 perhaps), yet the phenotypic and lifestyle change from a standard bear is considerable.[72][73] The transition could therefore be effected relatively swiftly.

Fossil discoveries

In the past thirty or so years there have been excavations in parts of the world which had scarcely been investigated before. Also, there is fresh appreciation of fossils discovered in the 19th century, but then denied or deprecated: the classic example is the Ediacaran biota from the immediate pre-Cambrian, after the Cryogenian period. These soft-bodied fossils are the first record of multicellular life. The interpretation of this fauna is still in flux.

Many outstanding discoveries have been made, and some of these have implications for evolutionary theory. The discovery of feathered dinosaurs and early birds from the Lower Cretaceous of Liaoning, N.E. China have convinced most students that birds did evolve from coelurosaurian theropod dinosaurs. Less well known, but perhaps of equal evolutionary significance, are the studies on early insect flight, on stem tetrapods from the Upper Devonian,[74][75] and the early stages of whale evolution.[76]

Recent work has shed light on the evolution of flatfish (pleuronectiformes), such as plaice, sole, turbot and halibut. Flatfish are interesting because they are one of the few vertebrate groups with external asymmetry. Their young are perfectly symmetrical, but the head is remodelled during a metamorphosis, which entails the migration of one eye to the other side, close to the other eye. Some species have both eyes on the left (turbot), some on the right (halibut, sole); all living and fossil flatfish to date show an ‘eyed’ side and a ‘blind’ side.[77] The lack of an intermediate condition in living and fossil flatfish species had led to debate about the origin of such a striking adaptation. The case was considered by Lamark,[78] who thought flatfish precursors would have lived in shallow water for a long period, and by Darwin, who predicted a gradual migration of the eye, mirroring the metamorphosis of the living forms. Darwin’s long-time critic St. George Mivart thought that the intermediate stages could have no selective value,[79] and in the 6th edition of the Origin, Darwin made a concession to the possibility of acquired traits.[80] Many years later the geneticist Richard Goldschmidt put the case forward as an example of evolution by saltation, bypassing intermediate forms.[81][82]

A recent examination of two fossil species from the Eocene has provided the first clear picture of flatfish evolution. The discovery of stem flatfish with incomplete orbital migration refutes Goldschmidt’s ideas, and demonstrates that “the assembly of the flatfish bodyplan occurred in a gradual, stepwise fashion”.[83] There are no grounds for thinking that incomplete orbital migration was maladaptive, because stem forms with this condition ranged over two geological stages, and are found in localities which also yield flatfish with the full cranial asymmetry. The evolution of flatfish falls squarely within the evolutionary synthesis.[77]

Horizontal gene transfer

Horizontal gene transfer (HGT) (or lateral gene transfer) is any process in which an organism gets genetic material from another organism without being the offspring of that organism.

Most thinking in genetics has focused on vertical transfer, but there is a growing awareness that horizontal gene transfer is a significant phenomenon. Amongst single-celled organisms it may be the dominant form of genetic transfer. Artificial horizontal gene transfer is a form of genetic engineering.

Richardson and Palmer (2007) state: “Horizontal gene transfer (HGT) has played a major role in bacterial evolution and is fairly common in certain unicellular eukaryotes. However, the prevalence and importance of HGT in the evolution of multicellular eukaryotes remain unclear.”[84]

The bacterial means of HGT are:


  • Transformation, the genetic alteration of a cell resulting from the introduction, uptake and expression of foreign genetic material (DNA or RNA).
  • Transduction, the process in which bacterial DNA is moved from one bacterium to another by a bacterial virus (a bacteriophage, or ‘phage’).
  • Bacterial conjugation, a process in which a bacterial cell transfers genetic material to another cell by cell-to-cell contact.
  • Gene transfer agent (GTA) is a virus-like element which contains random pieces of the host chromosome. They are found in most members of the alphaproteobacteria order Rhodobacterales.[85] They are encoded by the host genome. GTAs transfer DNA so frequently that they may have an important role in evolution.[86]
    A 2010 report found that genes for antibiotic resistance could be transferred by engineering GTAs in the laboratory.[85]


Some examples of HGT in metazoa are now known. Genes in bdelloid rotifers have been found which appear to have originated in bacteria, fungi, and plants. This suggests they arrived by horizontal gene transfer. The capture and use of exogenous (~foreign) genes may represent an important force in bdelloid evolution.[87][88] The team led by Matthew S. Meselson at Harvard University has also shown that, despite the lack of sexual reproduction, bdelloid rotifers do engage in genetic (DNA) transfer within a species or clade. The method used is not known at present.


1.       ^ “Appendix: Frequently Asked Questions” (php). Science and Creationism: a view from the National Academy of Sciences (Second ed.). Washington, DC: The National Academy of Sciences. 1999. p. 28. ISBN ISBN-0-309-06406-6. Retrieved September 24, 2009. “The scientific consensus around evolution is overwhelming.”

2.       ^ Mayr 2002, p. 270

3.       ^ Huxley 2010

4.       ^ Mayr & Provine 1998

5.       ^ Mayr E. 1982. The growth of biological thought: diversity, evolution & inheritance. Harvard, Cambs. p567 et seq.

6.       ^ Smocovitis, V. Betty. 1996. Unifying Biology: the evolutionary synthesis and evolutionary biology. Princeton University Press. p192

7.       ^ Gould S.J. Ontogeny and phylogeny. Harvard 1977. p221-2

8.       ^ Bowler P.J. 2003. Evolution: the history of an idea. pp236–256

9.       ^ a b Gould The Structure of Evolutionary Theory p. 216

10.    ^ Kutschera U. 2003. A comparative analysis of the Darwin-Wallace papers and the development of the concept of natural selection. Theory in Biosciences 122, 343-359

11.    ^ Bowler pp. 253–256

12.    ^ Mike Ambrose. “Mendel’s Peas”. Genetic Resources Unit, John Innes Centre, Norwich, UK. Retrieved 2007-09-22.

13.    ^ Bateson, William 1894. Materials for the study of variation, treated with special regard to discontinuity in the origin of species. The division of thought was between gradualists of the Darwinian school, and saltationists such as Bateson. Mutations (as ‘sports’) and polymorphisms were well known long before the Mendelian recovery.

14.    ^ Larson pp. 157–166

15.    ^ Grafen, Alan; Ridley, Mark (2006). Richard Dawkins: How A Scientist Changed the Way We Think. New York, New York: Oxford University Press. p. 69. ISBN 0-19-929116-0.

16.    ^ Bowler pp. 271–272

17.    ^ Transactions of the Royal Society of Edinburgh, 52:399–433

18.    ^ a b c d e f g h Larson Evolution: The Remarkable History of a Scientific Theory pp. 221–243

19.    ^ a b c d e f Bowler Evolution: The history of an Idea pp. 325–339

20.    ^ Gould The Structure of Evolutionary Theory pp. 503–518

21.    ^ Mayr & Provine 1998 p. 231

22.    ^ Dobzhansky T. 1951. Genetics and the Origin of Species. 3rd ed, Columbia University Press N.Y.

23.    ^ Ford E.B. 1964, 4th edn 1975. Ecological genetics. Chapman and Hall, London.

24.    ^ Mayr and Provine 1998 pp. 33–34

25.    ^ Smith, Charles H.. “Rensch, Bernhard (Carl Emmanuel) (Germany 1900–1990)”. Western Kentucky University. Retrieved 2007-09-22.

26.    ^ Mayr and Provine 1998 pp. 298–299, 416

27.    ^ Bowler p.361

28.    ^ Pigliucci, Massimo 2007. Do we need an extended evolutionary synthesis? Evolution 61 12, 2743–2749.

29.    ^ Dalrymple, G. Brent 2001. The age of the Earth in the twentieth century: a problem (mostly) solved. Special Publications, Geological Society of London 190, 205–221.

30.    ^ Van Andel, Tjeerd 1994. New views on an old planet: a history of global change. 2nd ed. Cambridge.

31.    ^ Witz A. 2006. The start of the world as we know it. Nature 442, p128.

32.    ^ Schopf J.W. and Klein (eds) 1992. The Proterozoic biosphere: a multi-disciplinary study. Cambridge University Press.

33.    ^ Lane, Nick 2002. Oxygen: the molecule that made the world. Oxford.

34.    ^ Schopf J.W. 1999. Cradle of life: the discovery of Earth’s earliest fossils. Princeton.

35.    ^ Yochelson, Ellis L. 1998. Charles Doolittle Walcott: paleontologist. Kent State, Ohio.

36.    ^ Knoll A.H. and Holland H.D. 1995. Oxygen and Proterozoic evolution: an update. In National Research Council, Effects of past climates upon life. National Academy, Washington D.C.

37.    ^ Huggett, Richard J. 1997. Catastrophism. new ed. Verso.

38.    ^ Hallam A. and Wignall P.B. 1997. Mass extinctions and their aftermath. Columbia, N.Y.

39.    ^ Elewa A.M.T. (ed) 2008. Mass extinctions. Springer, Berlin.

40.    ^ The terms (or their equivalents) were used as part of the synthesis by Simpson G.G. 1944. Tempo and mode in evolution, and Rensch B. 1947. Evolution above the species level. Columbia, N.Y. They were also used by some non-Darwinian evolutionists such as Yuri Filipchenko and Richard Goldschmidt. Here we use the terms as part of the evolutionary synthesis: they do not imply any change in mechanism.

41.    ^ Maynard Smith J. and Szathmáry E. 1997. The major transitions in evolution. Oxford.

42.    ^ de Bary, H.A. 1879. Die Erscheinung der Symbiose. Strassburg.

43.    ^ Khakhina, Liya Nikolaevna 1992. Concepts of symbiogenesis: a historical and critical study of the research of Russian scientists.

44.    ^ Wilson E.B. 1925. The cell in development and heredity . Macmillan, N.Y.

45.    ^ Wallin I.E. 1927. Symbionticism and the origin of species. Williams & Wilkins, Baltimore.

46.    ^ Wells H.G., Huxley J. and Wells G.P. 1930. The science of life. London vol 2, p505. This section (The ABC of genetics) was written by Huxley.

47.    ^ Sapp, January 1994. Evolution by association: a history of symbiosis. Oxford.

48.    ^ Lederberg J. 1952. Cell genetics and hereditary symbiosis. Physiological Reviews 32, 403–430.

49.    ^ Margulis L and Fester R (eds) 1991. Symbiosis as a source of evolutionary innovation. MIT.

50.    ^ Margulis L. 1993. Symbiosis in cell evolution: microbial communities in the Archaean and Proterozoic eras. Freeman, N.Y.

51.    ^ Maynard Smith J. and Szathmáry E. 1997. The major transitions in evolution. Oxford. The origin of the eukaryote cell is one of the seven major transitions, according to these authors.

52.    ^ Woese, Carl 1998. The Universal Ancestor. PNAS 95, 6854–6859.

53.    ^ Doolittle, W. Ford 1999. Phylogenetic classification and the Universal Tree. Science 284, 2124–2128.

54.    ^ Doolittle, W. Ford 2000. Uprooting the tree of life. Scientific American 282 (6): 90–95.

55.    ^ Dunn, Casey W. et al 2009. Broad phylogenetic sampling improves resolution of the animal tree of life. Nature 452, 745–749.

56.    ^ Laubichler M. and Maienschein J. 2007. From Embryology to Evo-Devo: a history of developmental evolution. MIT.

57.    ^ de Beer, Gavin 1930. Embryology and evolution. Oxford; 2nd ed 1940 as Embryos and ancestors; 3rd ed 1958, same title.

58.    ^ Bolk, L. 1926. Der Problem der Menschwerdung. Fischer, Jena.

59.    ^ short-list of 25 characters reprinted in Gould, Stephen Jay 1977. Ontogeny and phylogeny. Harvard. p357

60.    ^ Raff R.A. and Kaufman C. 1983. Embryos, genes and evolution: the developmental-genetic basis of evolutionary changes. Macmillan, N.Y.

61.    ^ Carroll, Sean B. 2005. Endless forms most beautiful: the new science of Evo-Devo and the making of the animal kingdom. Norton, N.Y.

62.    ^ Lewis E.B. 1995. The bithorax complex: the first fifty years. Nobel Prize lecture. Repr. in Ringertz N. (ed) 1997. Nobel lectures, Physiology or Medicine. World Scientific, Singapore.

63.    ^ Lawrence P. 1992. The making of a fly. Blackwell, Oxford.

64.    ^ Duncan I. 1987. The bithorax complex. Ann. Rev. Genetics 21, 285–319.

65.    ^ Lewis E.B. 1992. Clusters of master control genes regulate the development of higher organisms. J. Am. Medical Assoc. 267, 1524–1531.

66.    ^ McGinnis W. et al 1984. A conserved DNA sequence in homeotic genes of the Drosophila antennipedia and bithorax complexes. Nature 308, 428–433.

67.    ^ Scott M.P. and Weiner A.J. 1984. Structural relationships among genes that control developmental sequence homology between the antennipedia, ultrabithorax and fushi tarazu loci of Drosophila. PNAS USA 81, 4115.

68.    ^ Gehring W. 1999. Master control systems in development and evolution: the homeobox story. Yale.

69.    ^ Shubin N, Tabin C and Carroll S. 1997. Fossils, genes and the evolution of animal limbs. Nature 388, 639–648.

70.    ^ Shubin N, Tabin C and Carroll S. 2009. Deep homology and the origins of evolutionary novelty. Nature 457, p818–823.

71.    ^ Sarich V. 1976. The panda is a bear. Nature 245, 218–220.

72.    ^ Davies D.D. 1964. The giant panda: a morphological study of evolutionary mechanisms. Fieldiana Memoires (Zoology) 3, 1–339.

73.    ^ Stanley Steven M. 1979. Macroevolution: pattern & process. Freeman, San Francisco. p157

74.    ^ Clack, Jenny A. 2002. Gaining Ground: the origin and evolution of tetrapods. Bloomington, Indiana. ISBN 0-253-34054-3

75.    ^ “Jenny Clack homepage”.

76.    ^ Both whale evolution and early insect flight are discussed in Raff R.A. 1996. The shape of life. Chicago. These discussions provide a welcome synthesis of evo-devo and paleontology.

77.    ^ a b Janvier, Philip 2008. Squint of the fossil flatfish. Nature 454, 169

78.    ^ Lamark J.B. 1809. Philosophie zoologique. Paris.

79.    ^ Mivart St G. 1871. The genesis of species. Macmillan, London.

80.    ^ Darwin, Charles 1872. The origin of species. 6th ed, Murray, London. p186–188. The whole of Chapter 7 in this edition is taken up with answering critics of natural selection.

81.    ^ Goldschmidt R. Some aspects of evolution. Science 78, 539–547.

82.    ^ Goldschmidt R. 1940. The material basis of evolution. Yale.

83.    ^ Friedman, Matt 2008. The evolutionary origin of flatfish asymmetry. Nature 454, 209–212.

84.    ^ Richardson, Aaron O. and Jeffrey D. Palmer (January 2007). “Horizontal gene transfer in plants”. Journal of Experimental Botany 58 (1): 1–9 [1]. doi:10.1093/jxb/erl148. PMID 17030541.

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86.    ^ Maxmen A. 2010. Virus-like particles speed bacterial evolution. Nature. doi:10.1038/news.2010.507

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Jewish Views on Evolution

Jewish views on evolution, includes a continuum of views about evolution, creationism, and the origin of life. Today, many Jews accept the science of evolutionary theory and do not see it as incompatible with traditional Judaism, thus endorsing theistic evolution.

Classical Rabbinic Teachings

The vast majority of classical Rabbis hold that God created the world close to 6,000 years ago, and created Adam and Eve from clay. This view is based on a chronology developed in a midrash, Seder Olam, which was based on a literal reading of the Book of Genesis. It is attributed to the Tanna Yose ben Halafta, and covers history from the creation of the universe to the construction of the Second Temple in Jerusalem. Although it is known that a literal approach is not always needed when interpreting the Torah, there is a split over which parts are literal.

Most modern rabbis believe that the world is older, and that life as we know it today did not always exist. They believe such a view is needed to accept well-supported scientific theories, such as the theory of evolution. Rabbis who had this view based their conclusions on verses in the Talmud or in the midrash. For example:


  • Talmud Chaggiga 13b-14a states that there were 974 generations before God created Adam.
  • The Midrash[1] says: God created many worlds but was not satisfied, and left the world he was satisfied with.
  • Rabbi Moshe Ben Nacman (1194–1270) writes:[2] In the first day God created the energy (כח) “matter” (חומר) of all things, and then he was finished with the main creation. After that God created all other things from that energy.
  • Some midrashim state that the “first week” of Creation lasted for extremely long periods of time. See Anafim on Rabbenu Bachya’s Sefer Ikkarim 2:18; Midrash Bereshit Rabbah 9.
  • In Psalms it says “A thousand years is like a day in Your sight” (Psalm 90:4)


Medieval Rabbinic Teachings

In his commentary on the Torah, Rabbi Bahya ben Asher (11th century, Spain) concludes that there were many time systems occurring in the universe long before the spans of history that man is familiar with. Based on the Kabbalah he calculates that the Earth is billions of years old.

Some medieval philosophical rationalists, such as Maimonides and Gersonides[3] held that not every statement in Genesis is meant literally.[4] In this view, one was obligated to understand Torah in a way that was compatible with the findings of science. Indeed, Maimonides, one of the great Rabbis of the Middle Ages, wrote that if science and Torah were misaligned, it was either because science was not understood or the Torah was misinterpreted. Maimonides argued that if science proved a point that did not contradict any fundamentals of faith, then the finding should be accepted and scripture should be interpreted accordingly.[5] For example, in discussing Aristotle‘s view that the universe had existed literally forever, he argued that there was no convincing rational proof one way or the other, so that he (Maimonides) was free to accept, and therefore did accept, the Biblical view that the universe had come into being at a definite time; but that had Aristotle’s case been convincing on scientific grounds he would have been able to reinterpret Genesis accordingly.

Nahmanides, often critical of the rationalist views of Maimonides, pointed out (in his commentary to Genesis) several non-sequiturs stemming from a literal translation of the Bible’s account of Creation, and stated that the account actually symbolically refers to spiritual concepts. He quoted the Mishnah in Tractate Chagigah which states that the actual meaning of the Creation account, mystical in nature, was traditionally transmitted from teachers to advanced scholars in a private setting. Many classic Kabbalistic sources mention Shmitot – cosmic cycles of creation, similar to the Indian concept of yugas. Nahmanides’ disciple, Rabbi Isaac of Akko, a prominent Kabbalist of 13th-century, held that the Universe is about 15 billion years old.[citation needed] According to the tradition of Shmitot, Genesis talks openly only about the current epoch, while the information about the previous cosmic cycles is hidden in the esoteric reading of the text.

A literal interpretation of the biblical Creation story among classic rabbinic commentators is uncommon. Thus Bible commentator Abraham Ibn Ezra (11th Century) wrote,

If there appears something in the Torah which contradicts reason…then here one should seek for the solution in a figurative interpretation…the narrative of the tree of knowledge of good and evil, for instance, can only be understood in a figurative sense.

One of several notable exceptions may be the Tosafist commentary on Tractate Rosh Hashanah, where there seems to be an allusion to the age of creation according to a literal reading of Genesis. The non-literal approach is accepted by many as a possible approach within Modern Orthodox Judaism and some segments of Haredi Judaism.

Jewish Views in Reaction to Darwin

With the advent of Charles Darwin‘s evolutionary theory, the Jewish community found itself engaged in a discussion of Jewish principles of faith and modern scientific findings.

Post-1800 Kabbalistic views of compatibility

Rabbi Eliyahu Benamozegh, an Italian Kabbalist, wrote that were evolution to become a mainstay of scientific theory, it would not contradict the Torah as long as one understood it as having been guided by God.[6]

Rabbi Israel Lipschitz of Danzig (19th century) gave a famous lecture on Torah and paleontology, which is printed in the Yachin u-Boaz edition of the Mishnah, after Massechet Sanhedrin. He writes that Kabbalistic texts teach that the world has gone through many cycles of history, each lasting for many tens of thousands of years. He links these teachings to findings about geology from European, American and Asian geologists, and from findings from paleontologists. He discusses the wooly mammoth discovered in 1807 Siberia, Russia, and the remains of several then-famous dinosaur skeletons recently unearthed. Finding no contradiction between this and Jewish teachings, he states “From all this, we can see that all the Kabbalists have told us for so many centuries about the fourfold destruction and renewal of the Earth has found its clearest possible confirmation in our time.”

When scientists first developed the theory of evolution, this idea was seized upon by Rabbis such as Naftali Zvi Yehuda Berlin, known as the Netziv, who saw Kabbalah as a way to resolve the differences between traditional readings of the Bible and modern day scientific findings. He proposed that the ancient fossils of dinosaurs were the remains of beings that perished in the previous “worlds” described in midrash[7] and in some Kabbalistic texts. This was the view held by Rabbi Aryeh Kaplan (1934–1983).

Late 19th century Orthodox view of evolution

Samson Raphael Hirsch

In the late 1880s, Rabbi Samson Raphael Hirsch, an influential leader in the early opposition to non-Orthodox forms of Judaism, wrote that while he did not endorse the idea of common descent (that all life developed from one common organism), even if science ever did prove the factuality of Evolution, it would not pose a threat to Orthodox Judaism’s beliefs. He posited that belief in Evolution could instead cause one to be more reverent of God by understanding His wonders (a master plan for the universe).

This will never change, not even if the latest scientific notion that the genesis of all the multitudes of organic forms on earth can be traced back to one single, most primitive, primeval form of life should ever appear to be anything more than what it is today, a vague hypothesis still unsupported by fact. Even if this notion were ever to gain complete acceptance by the scientific world, Jewish thought, unlike the reasoning of the high priest of that notion, would nonetheless never summon us to revere a still extant representative of this primal form as the supposed ancestor of us all. Rather, Judaism in that case would call upon its adherents to give even greater reverence than ever before to the one, sole God Who, in His boundless creative wisdom and eternal omnipotence, needed to bring into existence no more than one single, amorphous nucleus and one single law of “adaptation and heredity” in order to bring forth, from what seemed chaos but was in fact a very definite order, the infinite variety of species we know today, each with its unique characteristics that sets it apart from all other creatures. (Collected Writings, vol. 7 pp. 263-264)

By the early to mid 1900s, the majority of Conservative Judaism and Reform Judaism came to accept the existence of evolution as a scientific fact. They interpreted Genesis and related Jewish teachings in light of this fact.

Modern day Orthodox Jewish views

The Rabbinical Council of America (RCA) has “maintained that evolutionary theory, properly understood, is not incompatible with belief in a Divine Creator, nor with the first 2 chapters of Genesis.” Prominent Orthodox rabbis who have affirmed that the world is older, and that life has evolved over time include Israel Lipschitz, Sholom Mordechai Schwadron (the MaHaRSHaM) (1835–1911), Zvi Hirsch Chajes (1805–1855) and Abraham Isaac Kook (1865–1935). These rabbis proposed their own versions of theistic evolution, in which the world is older, and that life does evolve over time in accord with natural law, painting natural law as the process by which God drives the world.

There is, in parallel, a discussion on this subject by scientists in the Orthodox Jewish community. One of the most prominent is Gerald Schroeder, an MIT trained physicist. He has written a number of articles and popular books attempting to reconcile Jewish theology with modern scientific findings that the world is billions of years old and that life has evolved over time. His work has received approbations from a number of Orthodox rabbinic authorities. Other physicists writing on this topic include Alvin Radkowsky, Nathan Aviezer, Herman Branover, Cyril Domb, Aryeh Kaplan and Yehuda (Leo) Levi.

Various popular works, citing an array of classical, Orthodox views, attempt to reconcile traditional Jewish texts with modern scientific findings concerning evolution, the age of the earth and the age of the Universe; these include:



Modern day Conservative Jewish views

Conservative Judaism embraces science as a way to learn about God’s creation, and like Orthodox and Reform Judaism, has not found the theory of evolution a challenge to traditional Jewish theology. The Conservative Jewish movement has not yet developed one official response to the subject, but a broad array of views has converged. Conservative Jews teach that God created the universe and is responsible for the creation of life within it, but proclaims no mandatory teachings about how this occurs at any level.

Many Conservative Rabbis embrace the term theistic evolution, and most reject the term intelligent design. Conservative rabbis who use the term intelligent design in their sermons often distinguish their views from the Christian fundamentalist use of this term. Like most in the scientific community, they understand “intelligent design” to be a technique by fundamentalist Christians to insert religion into public schools and to attack science, as admitted in the Intelligent design movement‘s wedge strategy position papers.

In contrast to fundamentalist views, Conservative Judaism strongly supports the use of science as the proper way to learn about the physical world in which we live, and thus encourages its adherents to find a way to understand evolution in a way that does not contradict the findings of peer-reviewed scientific research. The tension between accepting God’s role in the world and the findings of science, however, is not resolved, and a wide array of views exists. Some mainstream examples of Conservative Jewish thought are as follows:

Professor Ismar Schorsch, former chancellor of the Jewish Theological Seminary of America, writes that:

The Torah’s story of creation is not intended as a scientific treatise, worthy of equal time with Darwin’s theory of evolution in the curriculum of our public schools. The notes it strikes in its sparse and majestic narrative offer us an orientation to the Torah’s entire religious worldview and value system. Creation is taken up first not because the subject has chronological priority but rather to ground basic religious beliefs in the very nature of things. And I would argue that their power is quite independent of the scientific context in which they were first enunciated.

Rabbi David J. Fine, who has authorized official responsa for the Conservative movement’s Committee on Jewish Law and Standards, expresses a common Conservative Jewish view on the subject:

Conservative Judaism has always been premised on the total embrace of critical inquiry and science. More than being compatible with Conservative Judaism, I would say that it is a mitzvah to learn about the world and the way it works to the best of our abilities, since that is to marvel with awe at God’s handiwork. To not do so is sinful.

But here’s where the real question lies. Did God create the world, or not? Is it God’s handiwork? Many of the people who accept evolution, even many scientists, believe in what is called “theistic evolution,” that is, that behind the billions of years of cosmic and biological evolution, there is room for belief in a creator, God, who set everything into motion, and who stands outside the universe as the cause and reason for life. The difference between that and “intelligent design” is subtle yet significant. Believing scientists claim that belief in God is not incompatible with studying evolution since science looks only for the natural explanations for phenomena. The proponents of intelligent design, on the other hand, deny the ability to explain life on earth through solely natural explanations. That difference, while subtle, is determinative.

David J. Fine, Intelligent Design

Rabbi Michael Schwab writes:

…the Jewish view on the first set of questions is much closer to the picture painted by adherents to intelligent design than to those who are strict Darwinians. Judaism, as a religion, and certainly Conservative Judaism, sees creation as a purposeful process directed by God, however each individual defines the Divine. This is clearly in consonance with the theory of Intelligent Design. What Darwin sees as random, we see as the miraculous and natural unfolding of God’s subtle and beautiful plan.

…However, as unlikely as it may seem, this does not mean for one moment that Judaism’s view rejects wholesale the veracity of Darwin’s theory. In fact, I believe that it is easy to incorporate Darwin and Intelligent design into a meaningful conception of how we humans came into being…

We have frameworks built into our system to integrate the findings of science into our religious and theological beliefs. That is because we believe that the natural world, and the way it works, was created by God and therefore its workings must be consistent with our religious beliefs.

…One of the most well known ways our tradition has been able to hold onto both the scientific theory of evolution as well as the concept of a purposeful creation was by reading the creation story in Genesis in a more allegorical sense. One famous medieval commentary proclaims that the days of creation, as outlined in the book of Bereshit, could be seen as representative of the stages of creation and not literal 24 hour periods. Thus each Biblical day could have accounted for thousands or even millions of years. In that way the progression according to both evolution and the Torah remains essentially the same: first the elements were created, then the waters, the plants, the animals, and finally us. Therefore, Genesis and Darwin can both be right in a factual analysis even while we acknowledge that our attitudes towards these shared facts are shaped much more strongly by the Torah – we agree how the process unfolded but disagree that it was random.

Parshat Noah — November 4, 2005, How Did We Get Here? Michael Schwab

The claim that evolution is purposeful is in conflict with modern day evolutionary theory. The precise way in which God inserts design is not specified by Schwab or other rabbis.

Rabbi Lawrence Troster is a critic of positions such as this. He holds that much of Judaism (and other religions) have not successfully created a theology which allows for the role of God in the world and yet is also fully compatible with modern day evolutionary theory. Troster maintains that the solution to resolving the tension between classical theology and modern science can be found in process theology, such as in the writings of Hans Jonas, whose view of an evolving God within process philosophy contains no inherent contradictions between theism and scientific naturalism.

Lecture God after Darwin: Evolution and the Order of Creation October 21, 2004, Lishmah, New York City, Larry Troster

In a paper on Judaism and environmentalism, Troster writes:

Jonas is the only Jewish philosopher who has fully integrated philosophy, science, theology and environmental ethics. He maintained that humans have a special place in Creation, manifest in the concept that humans are created in the image of God. His philosophy is very similar to that of Alfred North Whitehead, who believed that God is not static but dynamic, in a continual process of becoming as the universe evolves.

From Apologetics to New Spirituality: Trends in Jewish Environmental Theology, Lawrence Troster

Jewish Opposition to Darwinian Theory

Whilst the Reform, Conservative and Modern Orthodox movements have stated that they feel there isn’t a conflict between evolutionary theory and the teachings of Judaism, some Haredi rabbis have remained staunchly opposed to certain teachings in evolutionary theory. In contrast with the literalist biblical interpretation of some Christian creationists, they express an openness to multiple interpretations of Genesis, through Jewish oral tradition and Jewish mysticism. They have also expressed an openness to evolutionary theory in biology, except where they perceive that it is in conflict with the Torah‘s account of creation.

Rabbi Avigdor Miller, a highly revered American Haredi Rabbi of the Lithuanian Yeshivah Tradition, who was also highly respected in Hasidic communities such as Satmar, was strongly opposed to the theory of Evolution, and wrote strong polemics against Evolution in several of his books, as well as speaking about this subject often in his popular lectures, taking a staunchly Creationist position. Several selections from his books on this subject were collected in a pamphlet he published in 1995 called “The Universe Testifies”.

Rabbi Menachem Mendel Schneerson, the last rebbe of the worldwide movement of Lubavticher or Chabad Hasidism, was avidly opposed to evolution, and his tremendous following remains largely committed to that position, though individual Chabad Hasidim may hold different views.

Rabbi Avi Shafran, a spokesman for Agudath Israel, writes a weekly column that is widely syndicated in the Jewish press. As an opponent of Darwinian evolutionary theory, Shafran is careful to distinguish the Jewish perspective from that of Christian fundamentalism. He writes, “An unfortunate side-effect of our affirmation of purpose in creation at a time of controversy is the assumption made by some that we believing Jews share some other groups’ broader skepticism of science. But while Torah-faithful Jews reject the blind worship of science, we do not regard science as an enemy.” Quite the contrary, Shafran remarks, Judaism seeks to learn as much as possible from God’s creation.

Shafran also rejects the literalism of Christian fundamentalism. He writes, “Nor is ‘Biblical literalism’ a Jewish approach. Many are the p’sukim (verses) that do not mean what a simple reading would yield.” To Shafran, the Jewish oral tradition is the key to the true meaning of the Torah’s words. “There are multiple levels of deeper meanings inaccessible to most of us. The words of Breishis (Genesis, Ashkenazi Hebrew) and the Midrashim thereon hide infinitely more than they reveal. It is clear that the Torah describes the creation of the universe as the willful act of HaKodosh Boruch Hu (the Holy One), and describes creation as having unfolded in stages. But details are hardly provided.”[8][9]

Moshe Feinstein

Rabbi Moshe Feinstein (1895–1986), a Orthodox posek who was known for his opposition to evolution, was one of the most famed Orthodox rabbis and decisors of Jewish Law for the ultra-Orthodox community. Rabbi Feinstein ruled that the reading of an evolutionary textbook is unequivocally forbidden, because belief in evolutionary history is tantamount to apikorsus (Hebrew, heresy). If a textbook was indispensable for other purposes, Feinstein directed that those pages containing references to evolution be torn out and discarded.[10]

Rabbi Moshe Feinstein (1895-1986)

Rabbi Shafran’s comments on intelligent design illustrate the distinction that Feinstein was making, that there is an essential difference between animals and humans that evolution does not uphold.

There is simply no philosophically sound way of holding simultaneously in one’s head both the conviction that we are mere evolved animals and the conviction that we are something qualitatively different. And no way to avoid the fact that when schoolchildren are taught biology, if they are taught to embrace the one, they are being taught to shun the other.”[8]

Responses to Feinstein’s ban

Torah MiTzion is a religious Zionist movement in Israel that promotes Torah study together with service in the Israel Defense Forces (IDF). In a commentary printed in the organization’s weekly newsletter, a writer states that study of evolution itself does not present a conflict with Jewish Law:

If biology is so prized a discipline, then so must be evolution — a central pillar of the life sciences. It is indisputable that organisms adapt to the environment via natural selection, as is evident for instance, by the development of antibiotic-resistant bacteria and antiretroviral-resistant HIV. Further indisputable is the fact that the same DNA which encodes the blueprint for simple organisms also encodes the blueprint for higher organisms (including human beings) with exquisitely minor variations, demonstrating that evolution need not be limited to microbes. Hence, one might expect on the basis of the foregoing that Halacha would welcome the study of evolution with open arms.[11]

Torah MiTzion resolves this conflict between Feinstein’s responsa on evolution and the observations of science by distinguishing between “evolution that we can observe” and “evolutionary history.” Its resolution of the matter allows for the study of evolution as a science, but forbids its use to “extrapolate backwards in time” to speculate on matters of creation:

Evolution that we can observe and measure with our senses is certainly part of the science curriculum that ought to be encouraged. But to extrapolate backwards in time on the basis of circumstantial evidence to so absurd an extent as to supplant the account of the creation of life given by the Torah with that of unverifiable human speculation is not a question of science but rather a revision of history.[11]

Slifkin affair

Rabbi Natan Slifkin

In 2004-2005, three popular books by Rabbi Natan Slifkin (sometimes pronounced Nosson Slifkin) were banned by a group of Haredi rabbinic authorities on the grounds that they were heretical. Known to his admirers as the “Zoo Rabbi,” Nosson Slifkin was the author of The Torah Universe, a series of books on science and religion that were widely read in Orthodox communities until they were suddenly banned. “The books written by Nosson Slifkin present a great stumbling block to the reader,” the ban declared. “They are full of heresy, twist and misrepresent the words of our sages and ridicule the foundations of our emunah (faith).” The ban, which prohibited Jews from reading, owning, or distributing Slifkin’s books, prompted a widespread backlash in the Orthodox Jewish community.

Jennie Rothenberg, reporting on this ban in the secular Jewish journal, Moment, asserted that the incident represents a major breaking point within ultra-Orthodox society. Rothenberg interviewed several rabbis who wished to remain anonymous. According to one of them, “Over the past 15 years, the rabbis of Bnai Brak and the more open American ultra-Orthodox rabbis have been split on a number of important policy decisions. The Slifkin ban is a huge break. It’s a kind of power struggle, and those who didn’t sign the ban are outraged right now. I’m talking about rabbis with long white beards who are furious about it.” Slifkin’s views, according to this rabbi, are shared by countless figures within the ultra-Orthodox community. “He’s saying out loud what a lot of people have been talking about quietly all along. To those people, he’s a kind of figurehead.” [12]

Orthodox Scientists Respond to Darwin

Several Modern Orthodox Jewish scientists have interpreted creation in light of both modern scientific findings and rabbinical interpretations of Genesis. Each of these scientists have claimed that modern science actually confirms a literal interpretation of Torah. All of them accept the scientific evidence that the age of the Earth and the age of the universe are on a scale of billions of years, and all of them acknowledge that the diversity of species on Earth can be explained through an evolutionary framework. However, each of them interprets certain aspects of evolution or the emergence of modern humans as a divine process, rather than a natural one. Thus, each of them accepts an evolutionary paradigm, while rejecting some aspects of Darwinism. Shai Cherry writes, “While twentieth century Jewish theologians have tended to compartmentalize science and the Torah, our Modern Orthodox physicists synthesized them.[13]


  • Nathan Aviezer, a physicist who trained at the University of Chicago, allows for divine guidance within an evolutionary paradigm in the transmutation of species over time, including the emergence of modern man from homo erectus. As a physicist, he interprets the six days of creation as broadly referring to large periods of time, an interpretation for which he cites rabbinic sources, including Maimonides and Nachmanides. For Aviezer, the evolutionary framework applies, except where the Hebrew verb bara (create) is used. To Aviezer, “It is particularly meaningful that Modern Man is intellectually and culturally so vastly superior to his closest relative, the extinct Neanderthal Man, even though both species are very similar.” He explains this through a literal interpretation of Genesis 1:27 — “And God created Man in His image.”[14]
  • Gerald Schroeder, an MIT trained physicist, believes that modern science contains nothing inimical to a literal reading of Genesis. Indeed, modern science allows one to understand the “true literal meaning of the Creation narrative.” To Schroeder, it is Einstein’s relativity, the “distortion of time facing backwards in a forward rushing cosmos,” that accounts for the compression of time in a 15-billion year-old universe into six days of creation. To Schroeder, the emergence of modern man can be dated to the beginning of writing. Archeologists date the first writing, he notes, “at five or six thousand years ago, the exact period that the Bible tells us the soul of Adam, the neshama, was created.” To Schroeder, who cites the Targum of Onkelos, Adam was the first man who could write, and the creation of Adam from more primitive man was a divine ensoulment.[15]
  • Judah Landa, a physicist and teacher at, among other institutions, the Yeshiva of Flatbush, takes a completely different approach. To Landa, genetic mutation is not a random process, but a divinely guided one that only appears random to humanity. “Evolution was designed and guided, just as the putting together of words and sentences into book forms is accomplished only by design and guidance. A book is designed by its author, evolution was (and continues to be) designed by the laws of nature (which in turn, were designed, we believe, by God).[16] Where Landa differs from Darwin is in his rejection of the Darwinian notion that evolution has no purpose. Landa does not claim that there is proof of a final purpose for life; he merely asserts that science cannot rule one out. He writes, “God may very well have designed the laws of the universe and the earliest forms of matter and energy with particular life-forms as end-products in mind. Evolution and natural selection may be the vehicles he chose and designed to achieve His purposes.”[17] Like Aviezar and Schroeder, Landa reconciles science with the biblical account of Genesis, taken literally, but he does so through literary interpretation.


Shai Cherry, Professor of Jewish Thought at Vanderbilt University, remarks that these Modern Orthodox scientists have rejected the approach taken by Jewish theologians. Theologians have tended to use later writings, such as Midrash and Kabbalah, to reconcile modern science with Genesis. The Orthodox scientists, by comparison, have largely ignored Jewish theology, in favor of a fundamentalist and literalist interpretation of Genesis. Yet in their writings, each of them seeks to reconcile science with Genesis. Cherry speculates, “They were targeting an American Jewish community that privileges science over Torah as a source of scientific knowledge. If Genesis could be shown to have anticipated Darwin or Einstein, then the Bible would regain an aura of truth that it had been losing since the advent of biblical criticism and modern science.”[18]

According to Cherry, the books of Aviezar, Schroeder, and Landa have each sought to strengthen Orthodox Jewry in a time of mounting secularization. Aviezar and Schroeder sought to prove that Genesis anticipates the findings of modern science, and thus increase its status. By contrast, Landa sought to remove a barrier to Orthodox commitment, by proving to secular Jews that Orthodox Judaism and modern science are compatible. At the same time, he sought to persuade students in his own Orthodox community that the study of science is not incompatible with commitment to Orthodoxy.[19]

Nathan Robertson a researcher in Biophysics has also released a book titled “The First Six Days” which reconciles the scientific theory of the beginnings of the universe and life with the biblical account of creation. Rabbinical sources are sited from Nachmanides (Ramban) and Rashi along with kabbilistic interpretations of Genesis. Nathan reconciles darwinian evolution with the biblical account and states that at deeper levels of understanding of the biblical text and of scientific theory, the two worlds overlap. “As one studies Science to deeper levels and also tries to study Bereshis to deeper levels, both principles begin to converge on each other.”

Jewish Reactions to Intelligent Design

The movement for intelligent design claims that an intelligent creator is responsible for the origin of life and of humankind. Its proponents claim that their hypothesis is a scientific theory that challenges the Darwinian view of evolution and its modern synthesis. Jewish theologians, organizations, and activists have maintained that intelligent design is not valid science but that it is a religious concept. Although some have expressed support for a theistic interpretation of evolution, they have generally rejected the tenets of the intelligent design movement itself. To Rabbi Brad Hirschfield, President of the National Jewish Center for Learning and Leadership, intelligent design is “their attempt to confirm what they already believe.”[20] Jewish organizations in the United States have been steadfast in their opposition to the teaching of intelligent design in public schools, charging that to do so would violate the separation of church and state.[21][22]


1.       ^ רבה בראשית ט אות ב

2.       ^ בראשית א א

3.       ^ Slifkin, Rabbi Natan. The Challenge of Creation, (New York: Yashar Books 2006) page 200.

4.       ^ Guide to the Perplexed, 2:17

5.       ^ Maimonides. The Guide for the Perplexed, Book II, chapter 25

6.       ^ Em LeMikra (Livorno 1863) commenting on Deuteronomy 22:10, page 87a-88b

7.       ^ מדרש רבה בראשית פרשה ט אות י

8.       ^ a b Menken, Yaakov (December 22, 2005). “Rabbi Avi Shafran on Intelligent Design”. Cross-Currents.

9.       ^ Rabbinical Council of America. “Creation, Evolution, and Intelligent Design”.

10.   ^ Feinstein, Moshe (5742/1982). Iggorot Moshe, Yoreh De’ah. 3:73. Noble Press. p. 323.

11.   ^ a b “Parshat Bereshit (Torah Commentary on Genesis)”. Torah MitZion.

12.   ^ Rothenberg, Jennie (October 2005). “The Heresy of Nosson Slifkin”. Moment Magazine.

13.   ^ Cherry(2006). 168.

14.   ^ Cherry(2006). 169-172.

15.   ^ Cherry(2006). 173-177.

16.   ^ Cherry(2006). 179.

17.   ^ Cherry(2006). 180.

18.   ^ Cherry(2006). 185.

19.   ^ Cherry(2006). 186.

20.   ^ Hirschfield, Brad. “The Origins of Life: A Jewish Perspective”. National Public Radio.

21.   ^ “AJC Applauds Court Decision against Intelligent Design in Pennsylvania Schools”. American Jewish Committee. December 20, 2005.

22.   ^ “Religion in the Science Class? Why Creationism and Intelligent Design Don’t Belong”. Anti-Defamation League.

Islamic Views on Evolution

Islamic views on evolution are diverse, ranging from theistic evolution to creationism. Muslims believe in a God as the Creator, as explained in the Qur’an. Throughout history some Muslim thinkers have proposed and accepted elements of the theory of evolution, while believing in the supremacy of God in the process. In modern times, some Muslims have rejected evolution, and teaching it is banned in some countries. The main schism between Islam and evolution is in the Adamic descent of human beings, a concept which modern biological anthropology rejects as mythology, supported by fossil evidence.[1]


The Qur’an does not contain a complete chronology of creation.[2] It declares variously that it took “six ayums” to create the “seven heavens [or firmaments] and earth”[3] An ‘ayum’ is defined as a stage, or a relative quantity of time rather than a 24 hour period,[2]. This ambiguity leaves the possibility of an old earth and a young earth is wholly excluded.

Islamic views of the Bible vary. In recent years, a movement has begun to emerge in some Muslim countries promoting themes that have been characteristic of Christian creationists. This stance has received some criticism[who?], due to claims that the Qur’an and Bible are incompatible.[4][5][6] Khalid Anees, president of the Islamic Society of Britain, has discussed the relationship between Islam and evolution:[7]

“Islam also has its own school of Evolutionary creationism/Theistic evolutionism, which holds that mainstream scientific analysis of the origin of the universe is supported by the Qur’an. Many Muslims believe in evolutionary creationism, especially among Sunni and Shia Muslims and the Liberal movements within Islam. Among scholars of Islam İbrahim Hakkı of Erzurum who lived in Erzurum then Ottoman Empire now Republic of Turkey in 18th century is famous of stating ‘between plants and animals there is sponge, and, between animals and humans there is monkey’.”[8]

Certain verses in the Qur’an are claimed by Muslims to be compatible with the expansion of the universe, Big Bang and Big Crunch theories:[9][10][11]

Pre-Modern Thought

Primitive evolutionary ideas have existed in the Muslim world ever since they were expressed by the Afro-Arab biologist Al-Jahiz (c. 776-869), who first described the struggle for existence, a precursor to natural selection.[12][13] Many other medieval Islamic philosophers and biologists later expressed evolutionary ideas, including Ibn Miskawayh, the Brethren of Purity,[14] Abu Rayhan Biruni,[15] Nasir al-Din Tusi[16] and Ibn Khaldun.[17][18]

Natural selection

The Mu’tazili scientist and philosopher al-Jahiz (c. 776-869) was the first of the Muslim biologists and philosophers to develop an early theory of evolution. He speculated on the influence of the environment on animals, considered the effects of the environment on the likelihood of an animal to survive, and first described the struggle for existence, a precursor to natural selection.[12][13][19] Al-Jahiz’s ideas on the struggle for existence in the Book of Animals have been summarized as follows:

“Animals engage in a struggle for existence; for resources, to avoid being eaten and to breed. Environmental factors influence organisms to develop new characteristics to ensure survival, thus transforming into new species. Animals that survive to breed can pass on their successful characteristics to offspring.”[20]

In Chapter 47 of his India, entitled “On Vasudeva and the Wars of the Bharata,” Abu Rayhan Biruni attempted to give a naturalistic explanation as to why the struggles described in the Mahabharata “had to take place.” He explains it using natural processes that include biological ideas related to evolution, which has led several scholars to compare his ideas to Darwinism and natural selection. This is due to Biruni describing the idea of artificial selection and then applying it to nature:[21]

“The agriculturist selects his corn, letting grow as much as he requires, and tearing out the remainder. The forester leaves those branches which he perceives to be excellent, whilst he cuts away all others. The bees kill those of their kind who only eat, but do not work in their beehive. Nature proceeds in a similar way; however, it does not distinguish for its action is under all circumstances one and the same. It allows the leaves and fruit of the trees to perish, thus preventing them from realising that result which they are intended to produce in the economy of nature. It removes them so as to make room for others.”

In the 13th century, Nasir al-Din al-Tusi explains how the elements evolved into minerals, then plants, then animals, and then humans. Tusi then goes on to explain how hereditary variability was an important factor for biological evolution of living things:[16]

“The organisms that can gain the new features faster are more variable. As a result, they gain advantages over other creatures. […] The bodies are changing as a result of the internal and external interactions.”

Tusi discusses how organisms are able to adapt to their environments:[16]

“Look at the world of animals and birds. They have all that is necessary for defense, protection and daily life, including strengths, courage and appropriate tools [organs] […] Some of these organs are real weapons, […] For example, horns-spear, teeth and claws-knife and needle, feet and hoofs-cudgel. The thorns and needles of some animals are similar to arrows. […] Animals that have no other means of defense (as the gazelle and fox) protect themselves with the help of flight and cunning. […] Some of them, for example, bees, ants and some bird species, have united in communities in order to protect themselves and help each other.”

Tusi then explains how humans evolved from advanced animals:[16]

“Such humans [probably anthropoid apes] live in the Western Sudan and other distant corners of the world. They are close to animals by their habits, deeds and behavior. […] The human has features that distinguish him from other creatures, but he has other features that unite him with the animal world, vegetable kingdom or even with the inanimate bodies.”

Transmutation of species

Al-Dinawari (828-896), considered the founder of Arabic botany for his Book of Plants, discussed plant evolution from its birth to its death, describing the phases of plant growth and the production of flowers and fruit.[22]

Material in Ibn Miskawayh‘s al-Fawz al-Asghar and the Brethren of Purity‘s Encyclopedia of the Brethren of Purity (The Epistles of Ikhwan al-Safa) has been criticized as overenthusiastic.[23] Muhammad Hamidullah describes their evolutionary ideas as follows:

“[These books] state that God first created matter and invested it with energy for development. Matter, therefore, adopted the form of vapour which assumed the shape of water in due time. The next stage of development was mineral life. Different kinds of stones developed in course of time. Their highest form being mirjan (coral). It is a stone which has in it branches like those of a tree. After mineral life evolves vegetation. The evolution of vegetation culminates with a tree which bears the qualities of an animal. This is the date-palm. It has male and female genders. It does not wither if all its branches are chopped but it dies when the head is cut off. The date-palm is therefore considered the highest among the trees and resembles the lowest among animals. Then is born the lowest of animals. It evolves into an ape. This is not the statement of Darwin. This is what Ibn Maskawayh states and this is precisely what is written in the Epistles of Ikhwan al-Safa. The Muslim thinkers state that ape then evolved into a lower kind of a barbarian man. He then became a superior human being. Man becomes a saint, a prophet. He evolves into a higher stage and becomes an angel. The one higher to angels is indeed none but God. Everything begins from Him and everything returns to Him.”[14]

English translations of the Encyclopedia of the Brethren of Purity were available from 1812.[24]

In the 14th century, Ibn Khaldun further developed the evolutionary ideas found in the Encyclopedia of the Brethren of Purity. The following statements from his 1377 work, the Muqaddimah, express evolutionary ideas:

“We explained there that the whole of existence in (all) its simple and composite worlds is arranged in a natural order of ascent and descent, so that everything constitutes an uninterrupted continuum. The essences at the end of each particular stage of the worlds are by nature prepared to be transformed into the essence adjacent to them, either above or below them. This is the case with the simple material elements; it is the case with palms and vines, (which constitute) the last stage of plants, in their relation to snails and shellfish, (which constitute) the (lowest) stage of animals. It is also the case with monkeys, creatures combining in themselves cleverness and perception, in their relation to man, the being who has the ability to think and to reflect. The preparedness (for transformation) that exists on either side, at each stage of the worlds, is meant when (we speak about) their connection.[25]

Plants do not have the same fineness and power that animals have. Therefore, the sages rarely turned to them. Animals are the last and final stage of the three permutations. Minerals turn into plants, and plants into animals, but animals cannot turn into anything finer than themselves.”[26]

Numerous other Islamic scholars and scientists, including the polymaths Ibn al-Haytham and Al-Khazini, discussed and developed these ideas. Translated into Latin, these works began to appear in the West after the Renaissance and may have had an impact on Western philosophy and science.[citation needed]

Modern Thought

In the 19th century the prominent scholar of Islamic revival, Jamal-al-Din al-Afghānī agreed with Darwin that life will compete with other life in order to succeed. He also believed that there was competition in the realm of ideas similar to that of nature. However, he was unwavering in his belief that God had to be the one controlling this process as a creator.[27] Another prominent and controversial Islamic Scholar, Ghulam Ahmad Pervez holds and defends the view that there is no contradiction between the scientific theory of evolution and Quran’s numerous references to the emergence of life in the universe.[28] The Ahmadiyya Muslim Movement’s view of evolution is that of universal acceptance, albeit divinely designed. The movement actively promotes it.[29] Over the course of several decades the movement has issued various publications in support of the scientific concepts behind evolution and frequently engage in promoting how it contends with religious scripture.

Adnan Oktar[30] is a prominent Muslim advocate against the theory of evolution. Most of his information is based on the Institute for Creation Research and the Intelligent Design movement in the United States.[31] His predecessor Said Nursi, led a similar campaign in the late 1970s. Oktar uses the Internet as one of the main methods for the promotion of his ideas.[32] His BAV (Bilim Araştırma Vakfı/ Science Research Foundation) organizes conferences with leading American creationists. Another leading Turkish advocate of Islamic creationism is Fethullah Gülen. Due to the lack of a detailed account of creation in the Qur’an, aspects other than the literal truth of the scripture are emphasized in the Islamic debate. The most important concept is the idea that there is no such thing as a random event, and that everything happens according to God’s will.

According to Guardian, some British Muslim students have distributed leaflets on campus, advocating against Darwin’s theory of evolution.[4] At a conference in the UK in January, 2004, entitled Creationism: Science and Faith in Schools, Dr Khalid Anees, president of the Islamic Society of Britain stated that “Muslims interpret the world through both the Koran and what is tangible and seen. There is no contradiction between what is revealed in the Koran and natural selection and survival of the fittest.”[7] Maurice Bucaille, famous in the Muslim world for his commentary on the Qur’an and science, has attempted to reconcile evolution with the Qur’an. He accepts animal evolution up to early hominid species and then posits a separate hominid evolution leading to modern humans. However, these ideas are still different from the theory of evolution as accepted by biologists.[31]

Muslim Society

Evolutionary biology is included in the high-school curricula of most Muslim countries. Science foundations of 14 Muslim countries, including Pakistan, Iran, Turkey, Indonesia, and Egypt, recently signed a statement by the Interacademy Panel (IAP, a global network of science academies), in support of the teaching of evolution, including human evolution.[31] Little is known about general societal views of evolution in Muslim countries.

A 2007 study of religious patterns found that only 8% of Egyptians, 11% of Malaysians, 14% of Pakistanis, 16% of Indonesians, and 22% of Turks agree that Darwin’s theory is probably or most certainly true, and a 2006 survey reported that about 25% of Turkish adults agreed that human beings evolved from earlier animal species. In contrast, the 2007 study found that only 28% of Kazakhs thought that evolution is false.[31] According to Salman Hameed, writing in the journal Science, there exists a contradictory attitude towards evolution in the Muslim world. While Muslims accept science as fully compatible with Islam, and most accept microevolution, very few Muslims accept the macroevolution as held by scientists, especially human evolution.[31]


1.       ^

2.       ^ a b “The Origin of Life: An Islamic perspective”. Islam for Today. Retrieved 2007-03-14.

3.       ^ “It is Allah who created the heavens and the earth and whatever is between them in six ayums”, Qur’an, Surah 32:4

4.       ^ a b Campbell, Duncan (2006-02-21). “Academics fight rise of creationism at universities”. Guardian.,,1714171,00.html. Retrieved 2008-07-19.

5.       ^ Sayin, Ümit; Kence, Aykut (1999). “Islamic Scientific Creationism: A New Challenge in Turkey”. National Center for Science Education. Retrieved 2009-11-12.

6.       ^ Koning, Danielle (2006). “Anti-evolutionism amongst Muslim students” (PDF). ISIM Review 18: 48. Retrieved 2007-03-14.

7.       ^ a b Papineau, David (2004-01-07). “Creationism: Science and Faith in Schools”. Guardian.,,1117752,00.html. Retrieved 2008-07-18.

8.       ^ Erzurumi, İ. H. (1257). Marifetname

9.       ^ Harun Yahya, The Big Bang Echoes through the Map of the Galaxy

10.    ^ Maurice Bucaille (1990), The Bible the Qur’an and Science, “The Quran and Modern Science”, ISBN 8171011322.

11.    ^ A. Abd-Allah, The Qur’an, Knowledge, and Science, University of Southern California.

12.    ^ a b Conway Zirkle (1941). Natural Selection before the “Origin of Species”, Proceedings of the American Philosophical Society 84 (1), p. 71-123.

13.    ^ a b Mehmet Bayrakdar (Third Quarter, 1983). “Al-Jahiz And the Rise of Biological Evolutionism”, The Islamic Quarterly. London.

14.    ^ a b Muhammad Hamidullah and Afzal Iqbal (1993), The Emergence of Islam: Lectures on the Development of Islamic World-view, Intellectual Tradition and Polity, p. 143-144. Islamic Research Institute, Islamabad.

15.    ^ Jan Z. Wilczynski (December 1959). “On the Presumed Darwinism of Alberuni Eight Hundred Years before Darwin”. Isis 50 (4): 459–466. doi:10.1086/348801

16.    ^ a b c d Farid Alakbarov (Summer 2001). A 13th-Century Darwin? Tusi’s Views on Evolution, Azerbaijan International 9 (2).

17.    ^ Franz Rosenthal and Ibn Khaldun, Muqaddimah, Chapter 6, Part 5

18.    ^ Franz Rosenthal and Ibn Khaldun, Muqaddimah, Chapter 6, Part 29

19.    ^ Paul S. Agutter & Denys N. Wheatley (2008). Thinking about Life: The History and Philosophy of Biology and Other Sciences. Springer. p. 43. ISBN 1402088655

20.    ^ Islam’s evolutionary legacy

21.    ^ Jan Z. Wilczynski (December 1959). “On the Presumed Darwinism of Alberuni Eight Hundred Years before Darwin”. Isis 50 (4): 459–466 [459–61]. doi:10.1086/348801

22.    ^ Fahd, Toufic. “Botany and agriculture”. pp. 815. , in (Morelon & Rashed 1996)

23.    ^ Footnote 27a to Chapter 6, Part 5 in Khaldūn, Ibn. The Muqaddimah. Franz Rosenthal (trans.).

24.    ^ “Ikhwan as-Safa and their Rasa’il: A Critical Review of a Century and a Half of Research”, by A. L. Tibawi, as published in volume 2 of The Islamic Quarterly in 1955; pgs. 28-46

25.    ^ Muqaddimah, Chapter 6, Part 5

26.    ^ Muqaddimah, Chapter 6, Part 29

27.    ^ al-Afghani, Jamal al-Din (1838-97)

28.    ^ Quran and the Theory of Evolution

29.    ^ Jesus and the Indian Messiah – 13. Every Wind of Doctrine

30.    ^ “Seeing the light — of science”. Retrieved 2009-01-06.

31.    ^ a b c d e Hameed S (2008). “Bracing for Islamic creationism”. Science 322 (5908): 1637–8. doi:10.1126/science.1163672. PMID 19074331.

32.    ^ Darwinism’s Contradiction with Religion, Why Darwinism is Incompatible With the Qur’an, Harun Yahya

History of Evolutionary Thought

Evolutionary thought, the conception that species change over time, has roots in antiquity, in the ideas of the ancient Greeks, Romans, and Chinese as well as in medieval Islamic science. However, with the beginnings of biological taxonomy in the late 17th century, Western biological thinking was influenced by two opposed ideas. One was essentialism, the belief that every species has essential characteristics that are unalterable, a concept which had developed from medieval Aristotelian metaphysics, and that fit well with natural theology. The other one was the development of the new anti-Aristotelian approach to modern science: as the Enlightenment progressed, evolutionary cosmology and the mechanical philosophy spread from the physical sciences to natural history. Naturalists began to focus on the variability of species; the emergence of paleontology with the concept of extinction further undermined the static view of nature. In the early 19th century, Jean-Baptiste Lamarck proposed his theory of the transmutation of species, the first fully formed theory of evolution.

The Tree of Life as depicted by Ernst Haeckel in The Evolution of Man (1879) illustrates the 19th-century view that evolution was a progressive process leading towards man.

In 1858, Charles Darwin and Alfred Russel Wallace published a new evolutionary theory that was explained in detail in Darwin’s On the Origin of Species (1859). Unlike Lamarck, Darwin proposed common descent and a branching tree of life, meaning that two very different species could have identical ancestry. The theory was based on the idea of natural selection, and it synthesized a broad range of evidence from animal husbandry, biogeography, geology, morphology, and embryology.

The debate over Darwin’s work led to the rapid acceptance of the general concept of evolution, but the specific mechanism he proposed, natural selection, was not widely accepted until it was revived by developments in biology that occurred during 1920s through the 1940s. Before that time most biologists argued that other factors were responsible for evolution. Alternatives to natural selection suggested during “the eclipse of Darwinism” (circa 1880 to 1920) included inheritance of acquired characteristics (neo-Lamarckism), an innate drive for change (orthogenesis), and sudden large mutations (saltationism). The synthesis of natural selection with Mendelian genetics during the 1920s and 1930s founded the new discipline of population genetics. Throughout the 1930s and 1940s, population genetics became integrated with other biological fields, resulting in a widely applicable theory of evolution that encompassed much of biology—the modern evolutionary synthesis.

Following the establishment of evolutionary biology, studies of mutation and variation in natural populations, combined with biogeography and systematics, led to sophisticated mathematical and causal models of evolution. Paleontology and comparative anatomy allowed more detailed reconstructions of the history of life. After the rise of molecular genetics in the 1950s, the field of molecular evolution developed, based on protein sequences and immunological tests, and later incorporating RNA and DNA studies. The gene-centered view of evolution rose to prominence in the 1960s, followed by the neutral theory of molecular evolution, sparking debates over adaptationism, the units of selection, and the relative importance of genetic drift versus natural selection. In the late 20th century, DNA sequencing led to molecular phylogenetics and the reorganization of the tree of life into the three-domain system. In addition, the newly recognized factors of symbiogenesis and horizontal gene transfer introduced yet more complexity into evolutionary theory. Discoveries in evolutionary biology have made a significant impact not just within the traditional branches of biology, but also in other academic disciplines (e.g., anthropology and psychology) and on society at large.[1]



Plato (left) and Aristotle (right), a detail of The School of Athens

Proposals that one type of animal, even humans, could descend from other types of animals, are known to go back to the first pre-Socratic Greek philosophers. Anaximander of Miletus (c.610–546 BC) proposed that the first animals lived in water, during a wet phase of the Earth’s past, and that the first land-dwelling ancestors of mankind must have been born in water, and only spent part of their life on land. He also argued that the first human of the form known today must have been the child of a different type of animal, because man needs prolonged nursing to live.[2] Empedocles (c. 490–430 BC), argued that what we call birth and death in animals are just the mingling and separations of elements which cause the countless “tribes of mortal things”.[3] Specifically, the first animals and plants were like disjointed parts of the ones we see today, some of which survived by joining in different combinations, and then intermixing, and wherever “everything turned out as it would have if it were on purpose, there the creatures survived, being accidentally compounded in a suitable way”.[4] Other philosophers, who became more influential in the Middle Ages, believed that the species of all things, not only living things, were fixed by divine design.

Plato (c. 428–348 BC) was called by biologist Ernst Mayr “the great antihero of evolutionism”, [5] because he promoted belief in essentialism, which is also referred to as the Theory of Forms. This theory holds that each natural type of object in the observed world is an imperfect manifestation of the ideal, form or “species” which defines that type. In his Timaeus for example, Plato has a character tell a story that the Demiurge created the cosmos and everything in it because, being good, and hence, “… free from jealousy, He desired that all things should be as like Himself as they could be”. The creator created all conceivable forms of life, since “… without them the universe will be incomplete, for it will not contain every kind of animal which it ought to contain, if it is to be perfect”. This “plenitude principle“—the idea that all potential forms of life are essential to a perfect creation—greatly influenced Christian thought.[6] However some historians of science have questioned how much influence Plato’s essentialism had on natural philosophy by stating that many philosophers after Plato believed that species might be capable of transformation and that the idea that biologic species were fixed and possessed unchangeable essential characteristics did not become important until the beginning of biologic taxonomy in the 17th and 18th centuries.[7]

Aristotle (384–322 BC), the most influential of the Greek philosophers in Europe in the Middle Ages, was a student of Plato and is also the earliest natural historian whose work has been preserved in any real detail. His writings on biology resulted from his research into natural history on and around the isle of Lesbos, and have survived in the form of four books, usually known by their Latin names, De anima (on the essence of life), Historia animalium (inquiries about animals), De generatione animalium (reproduction), and De partibus animalium (anatomy). Aristotle’s works contain some remarkably astute observations and interpretations—along with sundry myths and mistakes—reflecting the uneven state of knowledge during his time.[8] However, for Charles Singer, “Nothing is more remarkable than [Aristotle’s] efforts to [exhibit] the relationships of living things as a scala naturæ.”[8] This scala naturæ, described in Historia animalium, classified organisms in relation to a hierarchical “Ladder of Life” or “Chain of Being”, placing them according to their complexity of structure and function, with organisms that showed greater vitality and ability to move described as “higher organisms”.[6] Aristotle believed that features of living organisms showed clearly that they must have had what he called a final cause, that is to say that they had been designed for a purpose.[9] He explicitly rejected the view of Empedocles that living creatures might have originated by chance.[10]

Other Greek philosophers, such as Zeno of Citium (334–262 BC) the founder of the Stoic school of philosophy, agreed with Aristotle and other earlier philosophers that nature showed clear evidence of being designed for a purpose; this view is known as teleology.[11] The Roman stoic philosopher Cicero wrote that Zeno was known to have held the view, central to Stoic physics, that nature is primarily “directed and concentrated… to secure for the world… the structure best fitted for survival.”[12]


Ancient Chinese thinkers such as Zhuangzi (Chuang Tzu), a Taoist philosopher who lived around the 4th century BC, expressed ideas on changing biologic species. According to Joseph Needham, Taoism explicitly denies the fixity of biological species and Taoist philosophers speculated that species had developed differing attributes in response to differing environments.[13] Taoism regards humans, nature and the heavens as existing in a state of “constant transformation” known as the Tao, in contrast with the more static view of nature typical of Western thought.[14]


Titus Lucretius Carus (d. 50 BC), the Roman philosopher and atomist, wrote the poem On the Nature of Things (De rerum natura), which provides the best surviving explanation of the ideas of the Greek Epicurean philosophers. It describes the development of the cosmos, the Earth, living things, and human society through purely naturalistic mechanisms, without any reference to supernatural involvement. On the Nature of things would influence the cosmological and evolutionary speculations of philosophers and scientists during and after the Renaissance.[15][16] This view was in strong contrast with the views of Roman philosophers of the stoic school such as Marcus Tullius Cicero, Seneca, and Pliny the Elder who had a strongly teleological view of the natural world that influenced Christian theology.[11] Cicero reports that the peripatetic and stoic view of nature as an agency concerned most basically with producing life “best fitted for survival” was taken for granted among the Hellenistic elite.[12]

Augustine of Hippo

In line with earlier Greek thought, the 4th century bishop and theologian, Augustine of Hippo, wrote that the creation story in Genesis should not be read too literally. In his book De Genesi ad litteram (“On The Literal Interpretation of Genesis”), he stated that in some cases new creatures may have come about through the “decomposition” of earlier forms of life.[17] For Augustine, “plant, fowl and animal life are not perfect … but created in a state of potentiality”, unlike what he considered the theologically perfect forms of angels, the firmament and the human soul.[18] Augustine’s idea ‘that forms of life had been transformed “slowly over time”‘ prompted Father Giuseppe Tanzella-Nitti, Professor of Theology at the Pontifical Santa Croce University in Rome, to claim that Augustine had suggested a form of evolution.[19][20]

Middle Ages

Islamic philosophy and the struggle for existence

Although Greek and Roman evolutionary ideas died out in Europe after the fall of the Roman Empire, they were not lost to Islamic philosophers and scientists. In the Islamic Golden Age of the 8th to the 13th centuries, philosophers explored ideas about natural history. These ideas included transmutation from non-living to living: “from mineral to plant, from plant to animal, and from animal to man”.[21]

The first Muslim biologist and philosopher to publish detailed speculations about natural history, the Afro-Arab writer al-Jahiz, wrote in the 9th century. In the Book of Animals, he considered the effects of the environment on an animal’s chances for survival, and described the struggle for existence.[22] Al-Jahiz also wrote descriptions of food chains.[23] Al-Jahiz speculated on the influence of the environment on animals and considered the effects of the environment on the likelihood of an animal to survive. The Book of Animals states,

Animals engage in a struggle for existence; for resources, to avoid being eaten and to breed. Environmental factors influence organisms to develop new characteristics to ensure survival, thus transforming into new species. Animals that survive to breed can pass on their successful characteristics to offspring.[24][25]

His book was a major influence on Arab scholars of the 11th to 14th centuries, and the Latin translations of their work in turn became known to Charles Darwin’s predecessors, Linnaeus, Buffon and Lamarck.[24]

Some of Ibn Khaldun‘s thoughts, according to some commentators, anticipate the biological theory of evolution.[26] In 1377 Ibn Khaldun wrote the Muqaddimah in which he asserted that humans developed from “the world of the monkeys”, in a process by which “species become more numerous”[26] In chapter 1 he writes: “This world with all the created things in it has a certain order and solid construction. It shows nexuses between causes and things caused, combinations of some parts of creation with others, and transformations of some existent things into others, in a pattern that is both remarkable and endless.”[27]

The Muqaddimah also states in Chapter 6:

We explained there that the whole of existence in (all) its simple and composite worlds is arranged in a natural order of ascent and descent, so that everything constitutes an uninterrupted continuum. The essences at the end of each particular stage of the worlds are by nature prepared to be transformed into the essence adjacent to them, either above or below them. This is the case with the simple material elements; it is the case with palms and vines, (which constitute) the last stage of plants, in their relation to snails and shellfish, (which constitute) the (lowest) stage of animals. It is also the case with monkeys, creatures combining in themselves cleverness and perception, in their relation to man, the being who has the ability to think and to reflect. The preparedness (for transformation) that exists on either side, at each stage of the worlds, is meant when (we speak about) their connection.[28]

Christian philosophy and the great chain of being

Drawing of the great chain of being from Rhetorica Christiana (1579) by Diego Valades

During the Early Middle Ages, Greek classical learning was all but lost to the West. However, contact with the Islamic world, where Greek manuscripts were preserved and expanded, soon led to a massive spate of Latin translations in the 12th century. Europeans were re-introduced to the works of Plato and Aristotle, as well as to Islamic thought. Christian thinkers of the scholastic school, in particular Abelard and Thomas Aquinas, combined Aristotelian classification with Plato’s ideas of the goodness of God, and of all potential life forms being present in a perfect creation, to organize all inanimate, animate, and spiritual beings into a huge interconnected system: the scala naturæ, or great chain of being.[6][29]

Within this system, everything that existed could be placed in order, from “lowest” to “highest”, with Hell at the bottom and God at the top—below God, an angelic hierarchy marked by the orbits of the planets, mankind in an intermediate position, and worms the lowest of the animals. As the universe was ultimately perfect, the great chain was also perfect. There were no empty links in the chain, and no link was represented by more than one species. Therefore no species could ever move from one position to another. Thus, in this Christianized version of Plato’s perfect universe, species could never change, but remained forever fixed, in accordance with the text of Genesis. For humans to forget their position was seen as sinful, whether they behaved like lower animals or aspired to a higher station than was given them by their Creator.[6]

Creatures on adjacent steps were expected to closely resemble each other, an idea expressed in the saying: natura non facit saltum (“nature does not make leaps”).[6] This basic concept of the great chain of being greatly influenced the thinking of Western civilization for centuries (and still has an influence today). It formed a part of the argument from design presented by natural theology. As a classification system, it became the major organizing principle and foundation of the emerging science of biology in the 17th and 18th centuries.[6]

Thomas Aquinas on creation and natural processes

While the development of the great chain of being and the argument from design by Christian theologians contributed to the view that the natural world fit into an unchanging designed hierarchy, some theologians were more open to the possibility that the world might have developed through natural processes. Thomas Aquinas went even farther than Augustine of Hippo in arguing that scriptural texts like Genesis should not be interpreted in a literal way that conflicted with or constrained what natural philosophers learned about the workings of the natural world. He felt that the autonomy of nature was a sign of God’s goodness and that there was no conflict between the concept of a divinely created universe, and the idea that the universe may have evolved over time through natural mechanisms.[30] However, Aquinas disputed the views of those like the ancient Greek philosopher Empedocles who held that such natural processes showed that the universe could have developed without an underlying purpose. Rather holding that: “Hence, it is clear that nature is nothing but a certain kind of art, i.e., the divine art, impressed upon things, by which these things are moved to a determinate end. It is as if the shipbuilder were able to give to timbers that by which they would move themselves to take the form of a ship.”[31]

Renaissance and Enlightenment

Pierre Belon compared the skeletons of birds and humans in his Book of Birds (1555)

In the first half of the 17th century, René Descartes‘s mechanical philosophy encouraged the use of the metaphor of the universe as a machine, a concept that would come to characterise the scientific revolution.[32] Between 1650 and 1800 some evolutionists, such as Benoît de Maillet, produced theories that maintained that the universe, the earth, and life, had developed mechanically, without divine guidance.[33] In contrast, most contemporary theories of evolution, such of those of Gottfried Leibniz and J. G. Herder, regarded evolution as a fundamentally spiritual process.[34] In 1751, Pierre Louis Maupertuis veered toward more materialist ground. He wrote of natural modifications occurring during reproduction and accumulating over the course of many generations, producing races and even new species, a description that anticipated in general terms the concept of natural selection.[35]

Maupertuis’s ideas were in opposition to the influence of early taxonomists like John Ray. In the late 17th century Ray had given the first formal definition of a biological species, which he described as being characterized by essential unchanging features, and stated the seed of one species could never give rise to another.[7] The ideas of Ray and other 17th century taxonomists were influenced by natural theology and the argument from design.[36]

The word evolution (from the Latin evolutio, meaning “to unroll like a scroll”) was initially used to refer to embryological development; its first use in relation to development of species came in 1762, when Charles Bonnet used it for his concept of “pre-formation“, in which females carried a miniature form of all future generations. The term gradually gained a more general meaning of growth or progressive development.[37]

Later in the 18th century, the French philosopher G. L. L. Buffon, one of the leading naturalists of the time, suggested that what most people referred to as species were really just well-marked varieties, modified from an original form by environmental factors. For example, he believed that lions, tigers, leopards and house cats might all have a common ancestor. He further speculated that the 200 or so species of mammals then known might have descended from as few as 38 original animal forms. Buffon’s evolutionary ideas were limited; he believed each of the original forms had arisen through spontaneous generation and that each was shaped by “internal moulds” that limited the amount of change. Buffon’s works, Natural History and The Epochs of Nature, containing well developed theories about a completely materialistic origin for the Earth and his ideas questioning the fixity of species, were extremely influential.[38][39] Another French philosopher, Denis Diderot, also wrote that living things might have first arisen through spontaneous generation, and that species were always changing through a constant process of experiment where new forms arose and survived or not based on trial and error; an idea that can be considered a partial anticipation of natural selection.[40] Between 1767 and 1792, James Burnett, Lord Monboddo included in his writings not only the concept that man had descended from primates, but also that, in response to the environment, creatures had found methods of transforming their characteristics over long time intervals.[41] Charles Darwin’s grandfather, Erasmus Darwin, published Zoönomia in 1796, which suggested that “all warm-blooded animals have arisen from one living filament”.[42] In his 1802 poem Temple of Nature, he described the rise of life from minute organisms living in mud to all of its modern diversity.[43]

Early 19th century

Diagram of the geologic timescale from an 1861 book by Richard Owen showing the appearance of major animal types

Paleontology and geology

In 1796 Georges Cuvier published his findings on the differences between living elephants and those found in the fossil record. His analysis identified mammoths and mastodons as distinct species, different from any living animal, and effectively ended a long-running debate over whether a species could go extinct.[44] In 1788, James Hutton described gradual geological processes operating continuously over deep time.[45] In the 1790s William Smith began the process of ordering rock strata by examining fossils in the layers while he worked on his geologic map of England. Independently, in 1811, Georges Cuvier and Alexandre Brongniart published an influential study of the geologic history of the region around Paris, based on the stratigraphic succession of rock layers. These works helped establish the antiquity of the Earth.[46] Cuvier advocated catastrophism to explain the patterns of extinction and faunal succession revealed by the fossil record.

Knowledge of the fossil record continued to advance rapidly during the first few decades of the 19th century. By the 1840s, the outlines of the geologic timescale were becoming clear, and in 1841 John Phillips named three major eras, based on the predominant fauna of each: the Paleozoic, dominated by marine invertebrates and fish, the Mesozoic, the age of reptiles, and the current Cenozoic age of mammals. This progressive picture of the history of life was accepted even by conservative English geologists like Adam Sedgwick and William Buckland; however, like Cuvier, they attributed the progression to repeated catastrophic episodes of extinction followed by new episodes of creation.[47] Unlike Cuvier, Buckland and some other advocates of natural theology among British geologists made efforts to explicitly link the last catastrophic episode proposed by Cuvier to the biblical flood.[48][49]

From 1830 to 1833, Charles Lyell published his multi-volume work Principles of Geology, which, building on Hutton’s ideas, advocated a uniformitarian alternative to the catastrophic theory of geology. Lyell claimed that, rather than being the products of cataclysmic (and possibly supernatural) events, the geologic features of the Earth are better explained as the result of the same gradual geologic forces observable in the present day—but acting over immensely long periods of time. Although Lyell opposed evolutionary ideas (even questioning the consensus that the fossil record demonstrates a true progression), his concept that the Earth was shaped by forces working gradually over an extended period, and the immense age of the Earth assumed by his theories, would strongly influence future evolutionary thinkers such as Charles Darwin.[50]

Transmutation of species

Diagram from Vestiges of the Natural History of Creation (1844) by Robert Chambers shows a model of development where fish (F), reptiles (R), and birds (B) represent branches from a path leading to mammals (M).

Jean-Baptiste Lamarck proposed, in his Philosophie Zoologique of 1809, a theory of the transmutation of species. Lamarck did not believe that all living things shared a common ancestor but rather that simple forms of life were created continuously by spontaneous generation. He also believed that an innate life force drove species to become more complex over time, advancing up a linear ladder of complexity that was related to the great chain of being. Lamarck recognized that species were adapted to their environment. He explained this by saying that the same innate force driving increasing complexity caused the organs of an animal (or a plant) to change based on the use or disuse of those organs, just as muscles are affected by exercise. He argued that these changes would be inherited by the next generation and produce slow adaptation to the environment. It was this secondary mechanism of adaptation through the inheritance of acquired characteristics that would become known as Lamarckism and would influence discussions of evolution into the 20th century.[51][52]

A radical British school of comparative anatomy that included the anatomist Robert Grant was closely in touch with Lamarck’s French school of Transformationism. One of the French scientists who influenced Grant was the anatomist Étienne Geoffroy Saint-Hilaire, whose ideas on the unity of various animal body plans and the homology of certain anatomical structures would be widely influential and lead to intense debate with his colleague Georges Cuvier. Grant became an authority on the anatomy and reproduction of marine invertebrates. He developed Lamarck’s and Erasmus Darwin‘s ideas of transmutation and evolutionism, and investigated homology, even proposing that plants and animals had a common evolutionary starting point. As a young student Charles Darwin joined Grant in investigations of the life cycle of marine animals. In 1826 an anonymous paper, probably written by Robert Jameson, praised Lamarck for explaining how higher animals had “evolved” from the simplest worms; this was the first use of the word “evolved” in a modern sense.[53][54]

In 1844, the Scottish publisher Robert Chambers anonymously published an extremely controversial but widely read book entitled Vestiges of the Natural History of Creation. This book proposed an evolutionary scenario for the origins of the Solar System and life on Earth. It claimed that the fossil record showed a progressive ascent of animals with current animals being branches off a main line that leads progressively to humanity. It implied that the transmutations lead to the unfolding of a preordained plan that had been woven into the laws that governed the universe. In this sense it was less completely materialistic than the ideas of radicals like Robert Grant, but its implication that humans were only the last step in the ascent of animal life incensed many conservative thinkers. The high profile of the public debate over Vestiges, with its depiction of evolution as a progressive process, would greatly influence the perception of Darwin’s theory a decade later.[55][56]

Ideas about the transmutation of species were associated with the radical materialism of the Enlightenment and were attacked by more conservative thinkers. Georges Cuvier attacked the ideas of Lamarck and Geoffroy Saint-Hilaire, agreeing with Aristotle that species were immutable. Cuvier believed that the individual parts of an animal were too closely correlated with one another to allow for one part of the anatomy to change in isolation from the others, and argued that the fossil record showed patterns of catastrophic extinctions followed by re-population, rather than gradual change over time. He also noted that drawings of animals and animal mummies from Egypt, which were thousands of years old, showed no signs of change when compared with modern animals. The strength of Cuvier’s arguments and his scientific reputation helped keep transmutational ideas out of the mainstream for decades.[57]

This 1847 diagram by Richard Owen shows his conceptual archetype for all vertebrates.

In Britain the philosophy of natural theology remained influential. William Paley‘s 1802 book Natural Theology with its famous watchmaker analogy had been written at least in part as a response to the transmutational ideas of Erasmus Darwin.[58] Geologists influenced by natural theology, such as Buckland and Sedgwick, made a regular practice of attacking the evolutionary ideas of Lamarck, Grant, and The Vestiges of the Natural History of Creation.[59][60] Although the geologist Charles Lyell opposed scriptural geology, he also believed in the immutability of species, and in his Principles of Geology (1830–1833), he criticized Lamarck’s theories of development.[50] Idealists such as Louis Agassiz and Richard Owen believed that each species was fixed and unchangeable because it represented an idea in the mind of the creator. They believed that relationships between species could be discerned from developmental patterns in embryology, as well as in the fossil record, but that these relationships represented an underlying pattern of divine thought, with progressive creation leading to increasing complexity and culminating in humanity. Owen developed the idea of “archetypes” in the Divine mind that would produce a sequence of species related by anatomical homologies, such as vertebrate limbs. Owen led a public campaign that successfully marginalized Robert Grant in the scientific community. Darwin would make good use of the homologies analyzed by Owen in his own theory, but the harsh treatment of Grant, and the controversy surrounding Vestiges, showed him the need to ensure that his own ideas were scientifically sound.[54][61][62]

Anticipations of natural selection

Several writers anticipated aspects of Darwin’s theory, and in the third edition of On the Origin of Species published in 1861 Darwin named those he knew about in an introductory appendix, An Historical Sketch of the Recent Progress of Opinion on the Origin of Species, which he expanded in later editions.[63]

In 1813, William Charles Wells read before the Royal Society essays assuming that there had been evolution of humans, and recognising the principle of natural selection. Charles Darwin and Alfred Russel Wallace were unaware of this work when they jointly published the theory in 1858, but Darwin later acknowledged that Wells had recognised the principle before them, writing that the paper “An Account of a White Female, part of whose Skin resembles that of a Negro” was published in 1818, and “he distinctly recognises the principle of natural selection, and this is the first recognition which has been indicated; but he applies it only to the races of man, and to certain characters alone.”[64] When Darwin was developing his theory, he was influenced by Augustin de Candolle‘s natural system of classification, which laid emphasis on the war between competing species.[65][66]

Patrick Matthew wrote in the obscure book Naval Timber & Arboriculture (1831) of “continual balancing of life to circumstance. … [The] progeny of the same parents, under great differences of circumstance, might, in several generations, even become distinct species, incapable of co-reproduction.”[67] Charles Darwin discovered this work after the initial publication of the Origin. In the brief historical sketch that Darwin included in the 3rd edition he says “Unfortunately the view was given by Mr. Matthew very briefly in an Appendix to a work on a different subject … He clearly saw, however, the full force of the principle of natural selection.”[68]

It is possible to look through the history of biology from the ancient Greeks onwards and discover anticipations of almost all of Darwin’s key ideas. However, as historian of science Peter J. Bowler says, “Through a combination of bold theorizing and comprehensive evaluation, Darwin came up with a concept of evolution that was unique for the time.” Bowler goes on to say that simple priority alone is not enough to secure a place in the history of science; someone has to develop an idea and convince others of its importance to have a real impact.[69]

T. H. Huxley said in his essay on the reception of the Origin of Species:

The suggestion that new species may result from the selective action of external conditions upon the variations from their specific type which individuals present and which we call spontaneous because we are ignorant of their causation is as wholly unknown to the historian of scientific ideas as it was to biological specialists before 1858. But that suggestion is the central idea of the Origin of Species, and contains the quintessence of Darwinism.[70]

Darwin‘s first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837)

Natural selection

The biogeographical patterns Charles Darwin observed in places such as the Galapagos islands during the voyage of the Beagle caused him to doubt the fixity of species, and in 1837 Darwin started the first of a series of secret notebooks on transmutation. Darwin’s observations led him to view transmutation as a process of divergence and branching, rather than the ladder-like progression envisioned by Lamarck and others. In 1838 he read the new 6th edition of An Essay on the Principle of Population, written in the late 18th century by Thomas Malthus. Malthus’ idea of population growth leading to a struggle for survival combined with Darwin’s knowledge on how breeders selected traits, led to the inception of Darwin’s theory of natural selection. Darwin did not publish his ideas on evolution for 20 years. However he did share them with certain other naturalists and friends, starting with Joseph Hooker, with whom he discussed his unpublished 1844 essay on natural selection. During this period he used the time he could spare from his other scientific work to slowly refine his ideas and, aware of the intense controversy around transmutation, amass evidence to support them. In September 1854 he began full time work on writing his book on natural selection.[62][71][72]

Unlike Darwin, Alfred Russel Wallace, influenced by the book Vestiges of the Natural History of Creation, already suspected that transmutation of species occurred when he began his career as a naturalist. By 1855 his biogeographical observations during his field work in South America and the Malay Archipelago made him confident enough in a branching pattern of evolution to publish a paper stating that every species originated in close proximity to an already existing closely allied species. Like Darwin, it was Wallace’s consideration of how the ideas of Malthus might apply to animal populations that led him to conclusions very similar to those reached by Darwin about the role of natural selection. In February 1858 Wallace, unaware of Darwin’s unpublished ideas, composed his thoughts into an essay and mailed them to Darwin, asking for his opinion. The result was the joint publication in July of an extract from Darwin’s 1844 essay along with Wallace’s letter. Darwin also began work on a short abstract summarising his theory, which he would publish in 1859 as On the Origin of Species.[73]

Diagram by O.C. Marsh of the evolution of horse feet and teeth over time as reproduced in T.H Huxley‘s 1876 book Professor Huxley in America

1859–1930s: Darwin and his legacy

By the 1850s, whether or not species evolved was a subject of intense debate, with prominent scientists arguing both sides of the issue.[74] The publication of Charles Darwin‘s On the Origin of Species (1859) fundamentally transformed the discussion over biological origins.[75] Darwin argued that his branching version of evolution explained a wealth of facts in biogeography, anatomy, embryology, and other fields of biology. He also provided the first cogent mechanism by which evolutionary change could persist: his theory of natural selection.[76]

One of the first and most important naturalists to be convinced by Origin of the reality of evolution was the British anatomist Thomas Henry Huxley. Huxley recognized that unlike the earlier transmutational ideas of Lamarck and Vestiges, Darwin’s theory provided a mechanism for evolution without supernatural involvement, even if Huxley himself was not completely convinced that natural selection was the key evolutionary mechanism. Huxley would make advocacy of evolution a cornerstone of the program of the X Club to reform and professionalize science by displacing natural theology with naturalism and to end the domination of British natural science by the clergy. By the early 1870s in English-speaking countries, thanks partly to these efforts, evolution had become the mainstream scientific explanation for the origin of species.[76] In his campaign for public and scientific acceptance of Darwin’s theory, Huxley made extensive use of new evidence for evolution from paleontology. This included evidence that birds had evolved from reptiles, including the discovery of Archaeopteryx in Europe, and a number of fossils of primitive birds with teeth found in North America. Another important line of evidence was the finding of fossils that helped trace the evolution of the horse from its small five-toed ancestors.[77] However, acceptance of evolution among scientists in non-English speaking nations such as France, and the countries of southern Europe and Latin America was slower. An exception to this was Germany, where both August Weismann and Ernst Haeckel championed this idea: Haeckel used evolution to challenge the established tradition of metaphysical idealism in German biology, much as Huxley used it to challenge natural theology in Britain.[78] Haeckel and other German scientists would take the lead in launching an ambitious programme to reconstruct the evolutionary history of life based on morphology and embryology.[79]

Darwin’s theory succeeded in profoundly altering scientific opinion regarding the development of life and in producing a small philosophical revolution.[80] However, this theory could not explain several critical components of the evolutionary process. Specifically, Darwin was unable to explain the source of variation in traits within a species, and could not identify a mechanism that could pass traits faithfully from one generation to the next. Darwin’s hypothesis of pangenesis, while relying in part on the inheritance of acquired characteristics, proved to be useful for statistical models of evolution that were developed by his cousin Francis Galton and the “biometric” school of evolutionary thought. However, this idea proved to be of little use to other biologists.[81]

Application to humans

This illustration was the frontispiece of Thomas Henry Huxley‘s book Evidence as to Man’s Place in Nature (1863). Huxley applied Darwin’s ideas to humans, using comparative anatomy to show that humans and apes had a common ancestor, which challenged the theologically important idea that humans held a unique place in the universe.[82]

Charles Darwin was aware of the severe reaction in some parts of the scientific community against the suggestion made in Vestiges of the Natural History of Creation that humans had arisen from animals by a process of transmutation. Therefore he almost completely ignored the topic of human evolution in The Origin of Species. Despite this precaution, the issue featured prominently in the debate that followed the book’s publication. For most of the first half of the 19th century, the scientific community believed that, although geology had shown that the Earth and life were very old, human beings had appeared suddenly just a few thousand years before the present. However, a series of archaeological discoveries in the 1840s and 1850s showed stone tools associated with the remains of extinct animals. By the early 1860s, as summarized in Charles Lyell‘s 1863 book Geological Evidences of the Antiquity of Man, it had become widely accepted that humans had existed during a prehistoric period – which stretched many thousands of years before the start of written history. This view of human history was more compatible with an evolutionary origin for humanity than was the older view. On the other hand, at that time there was no fossil evidence to demonstrate human evolution. The only human fossils found before the discovery of Java man in the 1890s were either of anatomically modern humans or of Neanderthals that were too close, especially in the critical characteristic of cranial capacity, to modern humans for them to be convincing intermediates between humans and other primates.[83]

Therefore the debate that immediately followed the publication of The Origin of Species centered on the similarities and differences between humans and modern apes. Carolus Linnaeus had been criticized in the 18th century for grouping humans and apes together as primates in his ground breaking classification system.[84] Richard Owen vigorously defended the classification suggested by Cuvier and Johann Friedrich Blumenbach that placed humans in a separate order from any of the other mammals, which by the early 19th century had become the orthodox view. On the other hand, Thomas Henry Huxley sought to demonstrate a close anatomical relationship between humans and apes. In one famous incident, which became known as the Great Hippocampus Question, Huxley showed that Owen was mistaken in claiming that the brains of gorillas lacked a structure present in human brains. Huxley summarized his argument in his highly influential 1863 book Evidence as to Man’s Place in Nature. Another viewpoint was advocated by Charles Lyell and Alfred Russel Wallace. They agreed that humans shared a common ancestor with apes, but questioned whether any purely materialistic mechanism could account for all the differences between humans and apes, especially some aspects of the human mind.[83]

In 1871, Darwin published The Descent of Man, and Selection in Relation to Sex, which contained his views on human evolution. Darwin argued that the differences between the human mind and the minds of the higher animals were a matter of degree rather than of kind. For example, he viewed morality as a natural outgrowth of instincts that were beneficial to animals living in social groups. He argued that all the differences between humans and apes were explained by a combination of the selective pressures that came from our ancestors moving from the trees to the plains, and sexual selection. The debate over human origins, and over the degree of human uniqueness continued well into the 20th century.[83]

Alternatives to natural selection

This photo from Henry Fairfield Osborn’s 1918 book Origin and Evolution of Life shows models depicting the evolution of Titanothere horns over time, which Osborn claimed was an example of an orthogenetic trend in evolution.

The concept of evolution was widely accepted in scientific circles within a few years of the publication of Origin, but the acceptance of natural selection as its driving mechanism was much less widespread. The four major alternatives to natural selection in the late 19th century were theistic evolution, neo-Lamarckism, orthogenesis, and saltationism. Theistic evolution (a term promoted by Darwin’s greatest American advocate Asa Gray) was the idea that God intervened in the process of evolution to guide it in such a way that the living world could still be considered to be designed. However, this idea gradually fell out of favor among scientists, as they became more and more committed to the idea of methodological naturalism and came to believe that direct appeals to supernatural involvement were scientifically unproductive. By 1900, theistic evolution had largely disappeared from professional scientific discussions, although it retained a strong popular following.[85][86]

In the late 19th century, the term neo-Lamarckism came to be associated with the position of naturalists who viewed the inheritance of acquired characteristics as the most important evolutionary mechanism. Advocates of this position included the British writer and Darwin critic Samuel Butler, the German biologist Ernst Haeckel, and the American paleontologist Edward Drinker Cope. They considered Lamarckism to be philosophically superior to Darwin’s idea of selection acting on random variation. Cope looked for, and thought he found, patterns of linear progression in the fossil record. Inheritance of acquired characteristics was part of Haeckel’s recapitulation theory of evolution, which held that the embryological development of an organism repeats its evolutionary history.[85][86] Critics of neo-Lamarckism, such as the German biologist August Weismann and Alfred Russel Wallace, pointed out that no one had ever produced solid evidence for the inheritance of acquired characteristics. Despite these criticisms, neo-Lamarckism remained the most popular alternative to natural selection at the end of the 19th century, and would remain the position of some naturalists well into the 20th century.[85][86]

Orthogenesis was the hypothesis that life has an innate tendency to change, in a unilinear fashion, towards ever-greater perfection. It had a significant following in the 19th century, and its proponents included the Russian biologist Leo S. Berg and the American paleontologist Henry Fairfield Osborn. Orthogenesis was popular among some paleontologists, who believed that the fossil record showed a gradual and constant unidirectional change. Saltationism was the idea that new species arise as a result of large mutations. It was seen as a much faster alternative to the Darwinian concept of a gradual process of small random variations being acted on by natural selection, and was popular with early geneticists such as Hugo de Vries, William Bateson, and early in his career, T. H. Morgan. It became the basis of the mutation theory of evolution.[85][86]

Diagram from T. H. Morgan’s 1919 book The Physical Basis of Heredity, showing the sex-linked inheritance of the white-eyed mutation in Drosophila melanogaster

Mendelian genetics, biometrics, and mutation

The rediscovery of Gregor Mendel‘s laws of inheritance in 1900 ignited a fierce debate between two camps of biologists. In one camp were the Mendelians, who were focused on discrete variations and the laws of inheritance. They were led by William Bateson (who coined the word genetics) and Hugo de Vries (who coined the word mutation). Their opponents were the biometricians, who were interested in the continuous variation of characteristics within populations. Their leaders, Karl Pearson and Walter Frank Raphael Weldon, followed in the tradition of Francis Galton, who had focused on measurement and statistical analysis of variation within a population. The biometricians rejected Mendelian genetics on the basis that discrete units of heredity, such as genes, could not explain the continuous range of variation seen in real populations. Weldon’s work with crabs and snails provided evidence that selection pressure from the environment could shift the range of variation in wild populations, but the Mendelians maintained that the variations measured by biometricians were too insignificant to account for the evolution of new species.[87][88]

When T. H. Morgan began experimenting with breeding the fruit fly Drosophila melanogaster, he was a saltationist who hoped to demonstrate that a new species could be created in the lab by mutation alone. Instead, the work at his lab between 1910 and 1915 reconfirmed Mendelian genetics and provided solid experimental evidence linking it to chromosomal inheritance. His work also demonstrated that most mutations had relatively small effects, such as a change in eye color, and that rather than creating a new species in a single step, mutations served to increase variation within the existing population.[87][88]


Biston betularia f. typica is the white-bodied form of the peppered moth.

Biston betularia f. carbonaria is the black-bodied form of the peppered moth.

Population genetics

The Mendelian and biometrician models were eventually reconciled with the development of population genetics. A key step was the work of the British biologist and statistician R.A. Fisher. In a series of papers starting in 1918 and culminating in his 1930 book The Genetical Theory of Natural Selection, Fisher showed that the continuous variation measured by the biometricians could be produced by the combined action of many discrete genes, and that natural selection could change gene frequencies in a population, resulting in evolution. In a series of papers beginning in 1924, another British geneticist, J.B.S. Haldane, applied statistical analysis to real-world examples of natural selection, such as the evolution of industrial melanism in peppered moths, and showed that natural selection worked at an even faster rate than Fisher assumed.[89][90]

The American biologist Sewall Wright, who had a background in animal breeding experiments, focused on combinations of interacting genes, and the effects of inbreeding on small, relatively isolated populations that exhibited genetic drift. In 1932, Wright introduced the concept of an adaptive landscape and argued that genetic drift and inbreeding could drive a small, isolated sub-population away from an adaptive peak, allowing natural selection to drive it towards different adaptive peaks. The work of Fisher, Haldane and Wright founded the discipline of population genetics. This integrated natural selection with Mendelian genetics, which was the critical first step in developing a unified theory of how evolution worked.[89][90]

Modern evolutionary synthesis

In the first few decades of the 20th century, most field naturalists continued to believe that Lamarckian and orthogenetic mechanisms of evolution provided the best explanation for the complexity they observed in the living world. But as the field of genetics continued to develop, those views became less tenable.[91] Theodosius Dobzhansky, a postdoctoral worker in T. H. Morgan’s lab, had been influenced by the work on genetic diversity by Russian geneticists such as Sergei Chetverikov. He helped to bridge the divide between the foundations of microevolution developed by the population geneticists and the patterns of macroevolution observed by field biologists, with his 1937 book Genetics and the Origin of Species. Dobzhansky examined the genetic diversity of wild populations and showed that, contrary to the assumptions of the population geneticists, these populations had large amounts of genetic diversity, with marked differences between sub-populations. The book also took the highly mathematical work of the population geneticists and put it into a more accessible form. In Great Britain E.B. Ford, the pioneer of ecological genetics, continued throughout the 1930s and 1940s to demonstrate the power of selection due to ecological factors including the ability to maintain genetic diversity through genetic polymorphisms such as human blood types. Ford’s work would contribute to a shift in emphasis during the course of the modern synthesis towards natural selection over genetic drift.[89][90][92][93]

Evolutionary biologist Ernst Mayr was influenced by the work of the German biologist Bernhard Rensch showing the influence of local environmental factors on the geographic distribution of sub-species and closely related species. Mayr followed up on Dobzhansky’s work with the 1942 book Systematics and the Origin of Species, which emphasized the importance of allopatric speciation in the formation of new species. This form of speciation occurs when the geographical isolation of a sub-population is followed by the development of mechanisms for reproductive isolation. Mayr also formulated the biological species concept that defined a species as a group of interbreeding or potentially interbreeding populations that were reproductively isolated from all other populations.[89][90][94]

In the 1944 book Tempo and Mode in Evolution, George Gaylord Simpson showed that the fossil record was consistent with the irregular non-directional pattern predicted by the developing evolutionary synthesis, and that the linear trends that earlier paleontologists had claimed supported orthogenesis and neo-Lamarckism did not hold up to closer examination. In 1950, G. Ledyard Stebbins published Variation and Evolution in Plants, which helped to integrate botany into the synthesis. The emerging cross-disciplinary consensus on the workings of evolution would be known as the modern evolutionary synthesis. It received its name from the book Evolution: The Modern Synthesis by Julian Huxley.[89][90]

The evolutionary synthesis provided a conceptual core—in particular, natural selection and Mendelian population genetics—that tied together many, but not all, biological disciplines. It helped establish the legitimacy of evolutionary biology, a primarily historical science, in a scientific climate that favored experimental methods over historical ones.[95] The synthesis also resulted in a considerable narrowing of the range of mainstream evolutionary thought (what Stephen Jay Gould called the “hardening of the synthesis”): by the 1950s, natural selection acting on genetic variation was virtually the only acceptable mechanism of evolutionary change (panselectionism), and macroevolution was simply considered the result of extensive microevolution.[96][97]

1940s–1960s: Molecular biology and evolution

The middle decades of the 20th century saw the rise of molecular biology, and with it an understanding of the chemical nature of genes as sequences of DNA and of their relationship – through the genetic code – to protein sequences. At the same time, increasingly powerful techniques for analyzing proteins, such as protein electrophoresis and sequencing, brought biochemical phenomena into realm of the synthetic theory of evolution. In the early 1960s, biochemists Linus Pauling and Emile Zuckerkandl proposed the molecular clock hypothesis: that sequence differences between homologous proteins could be used to calculate the time since two species diverged. By 1969, Motoo Kimura and others provided a theoretical basis for the molecular clock, arguing that—at the molecular level at least—most genetic mutations are neither harmful nor helpful and that mutation and genetic drift (rather than natural selection) cause a large portion of genetic change: the neutral theory of molecular evolution.[98] Studies of protein differences within species also brought molecular data to bear on population genetics by providing estimates of the level of heterozygosity in natural populations.[99]

From the early 1960s, molecular biology was increasingly seen as a threat to the traditional core of evolutionary biology. Established evolutionary biologists—particularly Ernst Mayr, Theodosius Dobzhansky and G. G. Simpson, three of the architects of the modern synthesis—were extremely skeptical of molecular approaches, especially when it came to the connection (or lack thereof) to natural selection. The molecular-clock hypothesis and the neutral theory were particularly controversial, spawning the neutralist-selectionist debate over the relative importance of mutation, drift and selection, which continued into the 1980s without a clear resolution.[100][101]

Late 20th century

Gene-centered view

In the mid-1960s, George C. Williams strongly critiqued explanations of adaptations worded in terms of “survival of the species” (group selection arguments). Such explanations were largely replaced by a gene-centered view of evolution, epitomized by the kin selection arguments of W. D. Hamilton, George R. Price and John Maynard Smith.[102] This viewpoint would be summarized and popularized in the influential 1976 book The Selfish Gene by Richard Dawkins.[103] Models of the period showed that group selection was severely limited in its strength; though newer models do admit the possibility of significant multi-level selection.[104]

In 1973, Leigh Van Valen proposed the term “Red Queen“, which he took from Through the Looking-Glass by Lewis Carroll, to describe a scenario where a species involved in one or more evolutionary arms races would have to constantly change just to keep pace with the species with which it was co-evolving. Hamilton, Williams and others suggested that this idea might explain the evolution of sexual reproduction: the increased genetic diversity caused by sexual reproduction would help maintain resistance against rapidly evolving parasites, thus making sexual reproduction common, despite the tremendous cost from the gene-centric point of view of a system where only half of an organism’s genome is passed on during reproduction.[105][106] The gene-centric view has also led to an increased interest in Darwin’s old idea of sexual selection,[107] and more recently in topics such as sexual conflict and intragenomic conflict.


W. D. Hamilton’s work on kin selection contributed to the emergence of the discipline of sociobiology. The existence of altruistic behaviors has been a difficult problem for evolutionary theorists from the beginning.[108] Significant progress was made in 1964 when Hamilton formulated the inequality in kin selection known as Hamilton’s rule, which showed how eusociality in insects (the existence of sterile worker classes) and many other examples of altruistic behavior could have evolved through kin selection. Other theories followed, some derived from game theory, such as reciprocal altruism.[109] In 1975, E.O. Wilson published the influential and highly controversial book Sociobiology: The New Synthesis which claimed evolutionary theory could help explain many aspects of animal, including human, behavior. Critics of sociobiology, including Stephen Jay Gould and Richard Lewontin, claimed that sociobiology greatly overstated the degree to which complex human behaviors could be determined by genetic factors. They also claimed that the theories of sociobiologists often reflected their own ideological biases. Despite these criticisms, work has continued in sociobiology and the related discipline of evolutionary psychology, including work on other aspects of the altruism problem.[110][111]

A phylogenetic tree showing the three-domain system. Eukaryotes are colored red, Archaea green, and Bacteria blue.

Evolutionary paths and processes

One of the most prominent debates arising during the 1970s was over the theory of punctuated equilibrium. Niles Eldredge and Stephen Jay Gould proposed that there was a pattern of fossil species that remained largely unchanged for long periods (what they termed stasis), interspersed with relatively brief periods of rapid change during speciation.[112][113] Improvements in sequencing methods resulted in a large increase of sequenced genomes, allowing the testing and refining of evolutionary theories using this huge amount of genome data.[114] Comparisons between these genomes provide insights into the molecular mechanisms of speciation and adaptation.[115][116] These genomic analyses have produced fundamental changes in the understanding of the evolutionary history of life, such as the proposal of the three-domain system by Carl Woese.[117] Advances in computational hardware and software allow the testing and extrapolation of increasingly advanced evolutionary models and the development of the field of systems biology.[118] One of the results has been an exchange of ideas between theories of biological evolution and the field of computer science known as evolutionary computation, which attempts to mimic biological evolution for the purpose of developing new computer algorithms. Discoveries in biotechnology now allow the modification of entire genomes, advancing evolutionary studies to the level where future experiments may involve the creation of entirely synthetic organisms.[119]

Microbiology, horizontal gene transfer, and endosymbiosis

Microbiology was largely ignored by early evolutionary theory. This was due to the paucity of morphological traits and the lack of a species concept in microbiology, particularly amongst prokaryotes.[120] Now, evolutionary researchers are taking advantage of their improved understanding of microbial physiology and ecology, produced by the comparative ease of microbial genomics, to explore the taxonomy and evolution of these organisms.[121] These studies are revealing unanticipated levels of diversity amongst microbes.[122][123]

One particularly important outcome from studies on microbial evolution was the discovery in Japan of horizontal gene transfer in 1959.[124] This transfer of genetic material between different species of bacteria was first recognized because it played a major role in the spread of antibiotic resistance.[125] More recently, as knowledge of genomes has continued to expand, it has been suggested that lateral transfer of genetic material has played an important role in the evolution of all organisms.[126] These high levels of horizontal gene transfer have led to suggestions that the family tree of today’s organisms, the so-called “tree of life”, is more similar to an interconnected web or net.[127][128]

Indeed, the endosymbiotic theory for the origin of organelles sees a form of horizontal gene transfer as a critical step in the evolution of eukaryotes such as fungi, plants, and animals.[129][130] The endosymbiotic theory holds that organelles within the cells of eukorytes such as mitochondria and chloroplasts, had descended from independent bacteria that came to live symbiotically within other cells. It had been suggested in the late 19th century when similarities between mitochondria and bacteria were noted, but largely dismissed until it was revived and championed by Lynn Margulis in the 1960s and 70s; Margulis was able to make use of new evidence that such organelles had their own DNA that was inherited independently from that in the cell’s nucleus.[131]

Evolutionary developmental biology

In the 1980s and 1990s the tenets of the modern evolutionary synthesis came under increasing scrutiny. There was a renewal of structuralist themes in evolutionary biology in the work of biologists such as Brian Goodwin and Stuart Kauffman, which incorporated ideas from cybernetics and systems theory, and emphasized the self-organizing processes of development as factors directing the course of evolution. The evolutionary biologist Stephen Jay Gould revived earlier ideas of heterochrony, alterations in the relative rates of developmental processes over the course of evolution, to account for the generation of novel forms, and, with the evolutionary biologist Richard Lewontin, wrote an influential paper in 1979 suggesting that a change in one biological structure, or even a structural novelty, could arise incidentally as an accidental result of selection on another structure, rather than through direct selection for that particular adaptation. They called such incidental structural changes “spandrels” after an architectural feature.[132] Later, Gould and Vrba discussed the acquisition of new functions by novel structures arising in this fashion, calling them “exaptations“.[133]

Molecular data regarding the mechanisms underlying development accumulated rapidly during the 1980s and ’90s. It became clear that the diversity of animal morphology was not the result of different sets of proteins regulating the development of different animals, but from changes in the deployment of a small set of proteins that were common to all animals.[134] These proteins became known as the “developmental toolkit“.[135] Such perspectives influenced the disciplines of phylogenetics, paleontology and comparative developmental biology, and spawned the new discipline of evolutionary developmental biology also known as evo-devo.[136]

21st century

Macroevolution and microevolution

One of the tenets of the modern evolutionary synthesis was that macroevolution (the evolution of phylogenic clades at the species level and above) was solely the result of the mechanisms of microevolution (changes in gene frequency within populations) operating over an extended period of time. During the last decades of the 20th century some paleontologists raised questions about whether other factors, such as punctuated equilibrium and group selection operating on the level of entire species and even higher level phylogenic clades, needed to be considered to explain patterns in evolution revealed by statistical analysis of the fossil record. Near the end of the 20th century some researchers in evolutionary developmental biology suggested that interactions between the environment and the developmental process might have been the source of some of the structural innovations seen in macroevolution, but other evo-devo researchers maintained that genetic mechanisms visible at the population level are fully sufficient to explain all macroevolution.[137][138][139]

Epigenetic inheritance

Another place where developmental biology has led to the questioning of tenets of the modern evolutionary synthesis is the field of epigenetics, the study of how environmental factors affect the way genes express themselves during development. By the first decade of the 21st century it had become accepted that in some cases such environmental factors could affect the expression of genes in subsequent generations even though the offspring were not exposed to the same environmental factors, and there had been no genetic changes. This shows that in some cases non genetic changes to an organism can be inherited and it has been suggested that such inheritance can help with adaptation to local conditions and affect evolution.[140][141] Some have suggested that in certain cases a form of Lamarckian evolution may occur.[142]

Unconventional evolutionary theory

Omega Point

Pierre Teilhard de Chardin‘s metaphysical Omega Point Theory describes the gradual development of the universe from subatomic particles to human society, which he viewed as its final stage and goal.

Gaia hypothesis

Teilhard de Chardin’s ideas have been seen as being connected to the more specific Gaia theory by James Lovelock, who proposed that the living and nonliving parts of Earth can be viewed as a complex interacting system with similarities to a single organism.[143] The Gaia hypothesis has also been viewed by Lynn Margulis[144] and others as an extension of endosymbiosis and exosymbiosis.[145] This modified hypothesis postulates that all living things have a regulatory effect on the Earth’s environment that promotes life overall.


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Hindu Views on Evolution

Hinduism includes a range of viewpoints about the origin of life, creationism and evolution. The accounts of the emergence of life within the universe vary in description, but classically the god Brahma, from a Trimurti of three gods also including Vishnu and Shiva, is described as performing the act of ‘creation’, or more specifically of ‘propagating life within the universe’ with the other two deities being responsible for ‘preservation’ and ‘destruction’ (of the universe) respectively.[1] Some Hindu schools do not regard the scriptural creation myth as a literal truth, and often the creation stories themselves do not go into specific detail, thus leaving open the possibility of incorporating at least some theories in support of evolution. Some Hindus find support for, or foreshadowing of evolutionary ideas in scriptures, namely the Vedas.[2]

In India, the home country of Hindus; educated Hindus widely accept the theory of biological evolution. In a survey, 77% of respondents in India agreed that enough scientific evidence exists to support Charles Darwin’s Theory of Evolution, and 85 per cent of God-believing people said they believe in evolution as well.[3][4]

Hindu Creation Accounts

According to the Vedas creation of the universe is shrouded in mystery. The Nasadiya Sukta, the 129th hymn of the 10th Mandala of the Rigveda questions the attribution of creation and the origins of the universe:

Then was not non-existence nor existence: there was no realm of air, no sky beyond it. What covered in, and where?…. Who knows then whence it first came into being? He, the first origin of this creation, whether he formed it all or did not form it, Whose eye controls this world in highest heaven, he verily knows it, or perhaps he knows not. -(Rig Veda 10.129.1-7)[5]

A Hindu creation account is recorded in the Upanishads, according to which the universe and the Earth, along with humans and other creatures undergo repeated cycles (pralaya) of creation and destruction. A variety of myths exist regarding the specifics of the process, but in general the Hindu view of the cosmos is as eternal and cyclic.

Hindus and Evolution

Hindu cosmological view of creation

The Rig Veda questions the origin of the cosmos in:

Neither being (sat) nor non-being was as yet. What was concealed? And where? And in whose protection?…Who really knows? Who can declare it? Hence was it born, and whence came this creation? The devas were born later than this world’s creation, so who knows from where it came into existence? None can know from where creation has arisen, and whether he has or has not produced it. He who surveys it in the highest heavens, he alone knows-or perhaps does not know. (Rig Veda 10. 129)

The later puranic view asserts that the universe is created, destroyed, and re-created in an eternally repetitive series of cycles. In Hindu cosmology, a universe endures for about 4,320,000,000 years (one day of Brahma, the creator or kalpa)[6] and is then destroyed by fire or water elements. At this point, Brahma rests for one night, just as long as the day. This process, named pralaya (Cataclysm), repeats for 100 Brahma years (311 trillion, 40 billion human years) that represents Brahma’s lifespan. It must be noted that Brahma is the creator but not necessarily regarded as God in Hinduism. He is mostly regarded as a demigod or devata.

Day and Night of Brahma

Science writers Carl Sagan and Fritjof Capra have pointed out similarities between the latest scientific understanding of the age of the universe, and the Hindu concept of a “day and night of Brahma”, which is much closer to the current known age of the universe than other creation myths. The days and nights of Brahma posit a view of the universe that is divinely created, and is not strictly evolutionary, but an ongoing cycle of birth, death, and rebirth of the universe. According to Sagan:

The Hindu religion is the only one of the world’s great faiths dedicated to the idea that the Cosmos itself undergoes an immense, indeed an infinite, number of deaths and rebirths. It is the only religion in which time scales correspond to those of modern scientific cosmology. Its cycles run from our ordinary day and night to a day and night of Brahma, 8.64 billion years long, longer than the age of the Earth or the Sun and about half the time since the Big Bang.[7]

Capra, in his popular book The Tao of Physics, wrote that:

This idea of a periodically expanding and contracting universe, which involves a scale of time and space of vast proportions, has arisen not only in modern cosmology, but also in ancient Indian mythology. Experiencing the universe as an organic and rhythmically moving cosmos, the Hindus were able to develop evolutionary cosmologies which come very close to our modern scientific models.[8]

Daśāvatāras and evolution

British geneticist and evolutionary biologist, J B S Haldane, observed that the Dasavataras (ten principal avatars of Lord Vishnu) are a true sequential depiction of the great unfolding of evolution.[9] The avatars of Vishnu show an uncanny similarity to the biological theory of evolution of life on earth.[10]





First avatar is a fish, one which is creature living in water.

If we compare it with biological evolution on different Geological Time Scale first developed life was also in the form of fish which originated during Cambrian period.


Second avatar was in the form of Tortoise (reptiles).

In geology also first reptiles comes as second important evolution which originated in Mississippian period just after Amphibians.


Third avatar was in the form of Boar.

Evolution of the amphibian to the land animal.


The Man-Lion (Nara= man, simha=lion) was the fourth avatar.

But in geology no such evidences are mentioned. It may have been related with Ape Man The term may sometimes refer to extinct early human ancestors, such as the undiscovered missing link between apes and humans.


Fifth Avatar is the dwarf man.

It may be related with the first man originated during Pliocene. It may be related with Neanderthals. Neanderthals were generally only 12 to 14 cm (4½–5½ in) shorter than modern humans, contrary to a common view of them as “very short” or “just over 5 feet”.


The man with an axe was the sixth avatar.

It has the similarities with the first modern man originated during the Quaternary period or the man of Iron Age.

Hindu Creationism

According to Hindu creationism all species on earth including humans have “devolved” or come down from a highly state of pure consciousness. Hindu creationists claim that species of plants and animals are material forms adopted by pure consciousness which live an endless cycle of births and rebirths.[11] Ronald Numbers says that: “Hindu Creationists have insisted on the antiquity of humans, who they believe appeared fully formed as long, perhaps, as trillions of years ago.”[12] Hindu creationism is a form of old earth creationism, according to Hindu creationists the universe may even be older than billions of years. These views are based on the Vedas which depict an extreme antiquity of the universe and history of the earth.[13][14]

The Thiruvasakam, written by Appar in 8th Cent. AD, speaks about evolution. The descent of man is chronicled by and large along modern evolutionary order. It furthermore concludes that humankind is the most evolved animal.


Sculpture of Hanuman, a king among the Vanara, carrying the Dronagiri mountain

The Sanskrit writings of India mention creatures with apelike bodies and humanlike intelligence.[15] The Ramayana speaks of the Vanaras, a species of an apelike army of men that existed millions of years ago. According to the Ramayana alongside these ape-men existed modern humans.[16] Thus according to these ancient writings the status was a state of coexistence for certain durations which is very consistent with Darwinian evolution.

ISKCON and evolution

Members of the International Society for Krishna Consciousness (ISKCON) have expressed their belief that Charles Darwin’s theory of evolution by natural selection is false, but do not necessarily reject evolution altogether. The views of the founder of ISKCON, A.C. Bhaktivedanta Swami Prabhupada, on Darwin and evolution are found in his book Life comes from life.[17][18]


International Society for Krishna Consciousness (ISKCON) take a literal reading of Puranas which teach that time and space are cyclical, and that the earth goes through a cyclic model of yugas that says that life on earth devolves through four stages, or cosmic epochs, with each one becoming increasingly dark, alienated than the previous.[19][20][21]

History therefore to ISKCON is a succession of four epics called yugas, the first being the best a Golden age, then devolving to the present degenerate age, the Kali Yuga. After the Kali Yuga, the process repeats itself, with the earth entering a stage of sleep and then being reborn.[22] According to the teachings of ISKCON the current age we are now in, which began approximately 5000 years ago, is called Kali yuga. Kali-yuga is a 432000 year-long devolution, a stage of degeneration on earth and for the human being.[23]

ISKCON also teach another process of devolution. Michael Cremo defines this process of devolution as “The process by which conscious selves descend to the realm of the material energy, and are placed in material bodily vehicles.”[24] Cremo proposes that human beings have not evolved from other animals, but they have devolved down from a spiritual world.[25] This process of devolution is routed is the Hindu teaching of Sat Desh, (translated “True Home”) which teaches that a spiritual homeland exists eternally which is the location where spirits dwell before they enter material bodies on earth.[26]

According to the Vedic texts the remedy to free oneself from the evil of devolution, is to cast off materialism, and realize one’s real spiritual nature, which is that of Sat Desh, the homeland of spirits.[27] Vishal Mangalwadi describes Sat Desh as “The highest region, made purely of spirit substance and inhabited by pure spirits — pure because they are uncontaminated by matter or mind. There are countless spirits and they enjoy the greatest conceivable happiness”.[28]

Cremo is a member of ISKCON and the author of Human Devolution: A Vedic alternative to Darwin’s theory, published by ISKCON’s Bhaktivedanta Book Publishing,[29] which holds that man has existed on the earth in modern form far longer than that offered by the currently accepted fossil evidence and genetic evidence. Cremo suggests that Darwinian evolution should be replaced with “devolution” from the original unity with Brahman. His books have been met with considerable skepticism by the scientific community which charges that Cremo’s theories are pseudoscience.[30][31] Author Meera Nanda has dubbed these beliefs a form of “Vedic creationism.”[32]

As the cosmological theory of Hinduism teaches the four successively declining ‘ages’ of the yugas,[33] ISKCON teaches that we should expect to see evidence for devolution in biology and other sciences due to the “reality of the past Vedic curse of decay and degeneration on the world of nature, as stated in the Puranas”, ISKCON members claim that genes are being lost in animals and humans and this is evidence for devolution.[34]

Intelligent design

In 2010 the ISKCON Bhaktivedanta Book Trust published an intelligent design book titled Rethinking Darwin: A Vedic Study of Darwinism and Intelligent Design chapters included contributions from Intelligent design advocates William Dembski, Jonathan Wells and Michael Behe as well as from Hindu creationists Leif A. Jansen and Michael Cremo.[35]

Hindu Opposition to Christian Creationism

While the Creation-evolution controversy has seen much debate in the US and other countries, it has not been a significant issue in India, with its majority-Hindu population.[36][37] Hindus are among many faiths that have expressed apprehension about efforts to teach Christian creationism in public schools in the US.[38] One objection to the teaching of creationism based on the religious texts of a particular faith is that in a pluralistic society this can result in the imposition of one religion.[39]


1.       ^ “Religion & Ethics-Hinduism”. BBC. Retrieved 2008-12-26.

2.       ^ Moorty, J.S.R.L.Narayana (May 18–21, 1995). “Science and spirituality: Any Points of Contact? The Teachings of U.G.Krishnamurti: A Case Study”. Krishnamurti Centennial Conference. Retrieved 2008-12-26.

3.       ^

4.       ^ Hamilton, Fiona. The Times (London).

5.       ^ Griffith, Ralph T.H. (Transl.): Hymns of the Rgveda, Vol. II, 1889-92; Munshiram Manoharlal Publishers Pvt. Ltd., New Delhi, 1999.

6.       ^ A survey of Hinduism, Klaus K. Klostermaier, 2007, pp. 495-496

7.       ^ Sagan, Carl (1985). Cosmos. Ballantine Books. ISBN 978-0345331359. p. 258.

8.       ^ Capra, Fritjof (1991). Tao of Physics. Shambhala. ISBN 978-0877735946. p. 198

9.       ^ The India magazine of her people and culture, Volume 13, A. H. Advani, 1992, p. 92

10.    ^

11.    ^ Science & Religion: A New Introduction, Alister E. McGrath, 2009, p. 140

12.    ^ The creationists: from scientific creationism to intelligent design, Ronald L. Numbers, 2006, p. 420

13.    ^ James C. Carper, Thomas C. Hunt, The Praeger Handbook of Religion and Education in the United States: A-L, 2009, p. 167

14.    ^ A history of Indian philosophy, Volume 1, Surendranath Dasgupta, 1992, p. 10

15.    ^ J. K. Trikha, A study of the Ramayana of Valmiki, Bharatiya Vidya Bhavan, 1981

16.    ^ Lectures on Valmiki Ramayana, Balakanda, S. Appalacharyulu, C. Sita Ramamurti, 1980. p. 44

17.    ^ Life Comes from Life – written by A.C. Bhaktivedanta Swami Prabhupada (founder of ISKCON)

18.    ^ A selection of quotes and small essays – mostly by Bhaktivedanta Swami, founder of ISKCON, on Darwinian evolution and other topics.

19.    ^ The marriage of sense and soul: integrating science and religion, Random House, 1998, Ken Wilber

20.    ^ The Hare Krishna movement: the postcharismatic fate of a religious transplant, Maria Ekstrand, 2004, p. 12

21.    ^ Of gods, kings, and men: the reliefs of Angkor Wat, Thomas S. Maxwell, Jaroslav Poncar, Silkworm Books, 2006, p. 171

22.    ^ Historicizing “tradition” in the study of religion, Steven Engler, Gregory Price Grieve, 2005 p. 185

23.    ^ Back to godhead: the magazine of the Hare Krishna Movement, Volume 23, Baktivendanta Book Trust, 1988, p. 71

24.    ^ Human devolution: a Vedic alternative to Darwin’s theory, Michael Cremo, Bhaktivedanta Book Pub., 2003, p. 488

25.    ^ Scientific values and civic virtues, Noretta Koertge, Oxford University Press, 2005, p. 232

26.    ^ The path of the masters: the science of Surat shabd yoga, the Yoga of the Audible Life Stream, Julian Johnson, Radha Soami Satsang Beas, 1985, pp. 204-206

27.    ^ Darshana international, Volume 21, J.P. Atreya, 1981, pp. 28-29

28.    ^ The world of gurus, Vishal Mangalwadi, Vikas Pub. House, 1977, p. 203

29.    ^ Cremo, Michael (2003). Human Devolution: A Vedic alternative to Darwin’s theory. Bhaktivedanta Book Publishing. ISBN 0892133341.

30.    ^ Forbidden Archaeology´s Impact by Michael A Cremo, Tom Morrow, Reports of the National Center for Science Education, 19 (3): 14-17.

31.    ^ Forbidden Archaeology : Antievolutionism Outside the Christian Arena, Wade Tarzia, Creation/Evolution 34:13-25, 1994

32.    ^ Nanda, Meera, Vedic creationism in America, Frontline, Vol 23, Issue 01, Jan. 14 – 27, 2006.

33.    ^ Is the goddess a feminist?: the politics of South Asian goddesses, Alf Hiltebeitel, Kathleen M. Erndl,Sheffield Academic Press, 2000, p. 58

34.    ^

35.    ^

36.    ^ Balaram, P (2004). “Editorial”. Current Science 86 (9): 1191–1192.

37.    ^ Coleman, Simon; Carlin, Leslie (2003). “The cultures of creationism: Shifting boundaries of belief, knowledge and nationhood”. The Cultures of Creationism: Anti-evolutionism in English-speaking Countries. Ashgate Publishing. p. 3. ISBN 075460912X.

38.    ^ “Christian agenda worries other faiths: push for intelligent design seen by some as imposing Christianity on others”, Jim Baker, Lawrence World – Journal, May 12, 2005. See article on LJ world

39.    ^ White, Aaron. “The debate over evolution in Kansas public schools”. The Pluralism Project at Harvard University. Retrieved 2008-12-26.


Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.[1]

Life on Earth originated and then evolved from a universal common ancestor approximately 3.7 billion years ago. Repeated speciation and the divergence of life can be inferred from shared sets of biochemical and morphological traits, or by shared DNA sequences. These homologous traits and sequences are more similar among species that share a more recent common ancestor, and can be used to reconstruct evolutionary histories, using both existing species and the fossil record. Existing patterns of biodiversity have been shaped both by speciation and by extinction.[2]

Charles Darwin was the first to formulate a scientific argument for the theory of evolution by means of natural selection. Evolution by natural selection is a process that is inferred from three facts about populations: 1) more offspring are produced than can possibly survive, 2) traits vary among individuals, leading to differential rates of survival and reproduction, and 3) trait differences are heritable.[3] Thus, when members of a population die they are replaced by the progeny of parents that were better adapted to survive and reproduce in the environment in which natural selection took place. This process creates and preserves traits that are seemingly fitted for the functional roles they perform.[4] Natural selection is the only known cause of adaptation, but not the only known cause of evolution. Other, nonadaptive causes of evolution include mutation and genetic drift.[5]

In the early 20th century, genetics was integrated with Darwin’s theory of evolution by natural selection through the discipline of population genetics. The importance of natural selection as a cause of evolution was accepted into other branches of biology. Moreover, previously held notions about evolution, such as orthogenesis and “progress” became obsolete.[6] Scientists continue to study various aspects of evolution by forming and testing hypotheses, constructing scientific theories, using observational data, and performing experiments in both the field and the laboratory. Biologists agree that descent with modification is one of the most reliably established facts in science.[7] Discoveries in evolutionary biology have made a significant impact not just within the traditional branches of biology, but also in other academic disciplines (e.g., anthropology and psychology) and on society at large.[8][9]

History of Evolutionary Thought

The proposal that one type of animal could descend from an animal of another type goes back to some of the first pre-Socratic Greek philosophers, such as Anaximander and Empedocles.[10][11] In contrast to these materialistic views, Aristotle understood all natural things, not only living things, as being imperfect actualisations of different fixed natural possibilities, known as “forms“, “ideas“, or (in Latin translations) “species”.[12][13] This was part of his teleological understanding of nature in which all things have an intended role to play in a divine cosmic order. Variations of this idea became the standard understanding of the Middle Ages, and were integrated into Christian learning, but Aristotle did not demand that real types of animals corresponded one-for-one with exact metaphysical forms, and specifically gave examples of how new types of living things could come to be.[14]” >In the 17th century the new method of modern science rejected Aristotle’s approach, and sought explanations of natural phenomena in terms of laws of nature which were the same for all visible things, and did not need to assume any fixed natural categories, nor any divine cosmic order. But this new approach was slow to take root in the biological sciences, which became the last bastion of the concept of fixed natural types. John Ray used one of the previously more general terms for fixed natural types, “species”, to apply to animal and plant types, but unlike Aristotle he strictly identified each type of living thing as a species, and proposed that each species can be defined by the features that perpetuate themselves each generation.[15] These species were designed by God, but showing differences caused by local conditions. The biological classification introduced by Carolus Linnaeus in 1735 also viewed species as fixed according to a divine plan.[16] 

In 1842 Charles Darwin penned his first sketch of what became On the Origin of Species.[17]

Other naturalists of this time speculated on evolutionary change of species over time according to natural laws. Maupertuis wrote in 1751 of natural modifications occurring during reproduction and accumulating over many generations to produce new species.[18] Buffon suggested that species could degenerate into different organisms, and Erasmus Darwin proposed that all warm-blooded animals could have descended from a single micro-organism (or “filament”).[19] The first fully-fledged evolutionary scheme was Lamarck‘s “transmutation” theory of 1809 which envisaged spontaneous generation continually producing simple forms of life developed greater complexity in parallel lineages with an inherent progressive tendency, and that on a local level these lineages adapted to the environment by inheriting changes caused by use or disuse in parents.[20][21] (The latter process was later called Lamarckism.)[20][22][23][24] These ideas were condemned by establishment naturalists as speculation lacking empirical support. In particular Georges Cuvier insisted that species were unrelated and fixed, their similarities reflecting divine design for functional needs. In the meantime, Ray’s ideas of benevolent design had been developed by William Paley into a natural theology which proposed complex adaptations as evidence of divine design, and was admired by Charles Darwin.[25][26][27]

The critical break from the concept of fixed species in biology began with the theory of evolution by natural selection, which was formulated by Charles Darwin. Partly influenced by An Essay on the Principle of Population by Thomas Robert Malthus, Darwin noted that population growth would lead to a “struggle for existence” where favorable variations could prevail as others perished. Each generation, many offspring fail to survive to an age of reproduction because of limited resources. This could explain the diversity of animals and plants from a common ancestry through the working of natural laws working the same for all types of thing.[28][29][30][31] Darwin was developing his theory of “natural selection” from 1838 onwards until Alfred Russel Wallace sent him a similar theory in 1858. Both men presented their separate papers to the Linnean Society of London.[32] At the end of 1859, Darwin’s publication of On the Origin of Species explained natural selection in detail and in a way that lead to an increasingly wide acceptance of Darwinian evolution. Thomas Henry Huxley applied Darwin’s ideas to humans, using paleontology and comparative anatomy to provide strong evidence that humans and apes shared a common ancestry. Some were disturbed by this since it implied that humans did not have a special place in the universe.[33]

Precise mechanisms of reproductive heritability and the origin of new traits remained a mystery. Towards this end, Darwin developed his provisional theory of pangenesis.[34] In 1865 Gregor Mendel reported that traits were inherited in a predictable manner through the independent assortment and segregation of elements (later known as genes). Mendel’s laws of inheritance eventually supplanted most of Darwin’s pangenesis theory.[35] August Weismann made the important distinction between germ cells (sperm and eggs) and somatic cells of the body, demonstrating that heredity passes through the germ line only. Hugo de Vries connected Darwin’s pangenesis theory to Wiesman’s germ/soma cell distinction and proposed that Darwin’s pangenes were concentrated in the cell nucleus and when expressed they could move into the cytoplasm to change the cells structure. De Vries was also one of the researchers who made Mendel’s work well-known, believing that Mendelian traits corresponded to the transfer of heritable variations along the germline.[36] To explain how new variants originate, De Vries developed a mutation theory that led to a temporary rift between those who accepted Darwinian evolution and biometricians who allied with de Vries.[21][37][38] At the turn of the 20th century, pioneers in the field of population genetics, such as J.B.S. Haldane, Sewall Wright, and Ronald Fisher, set the foundations of evolution onto a robust statistical philosophy. The false contradiction between Darwin’s theory, genetic mutations, and Mendelian inheritance was thus reconciled.[39]

In the 1920s and 1930s a modern evolutionary synthesis connected natural selection, mutation theory, and Mendelian inheritance into a unified theory that applied generally to any branch of biology. The modern synthesis was able to explain patterns observed across species in populations, through fossil transitions in palaeontology, and even complex cellular mechanisms in developmental biology.[21][40] The publication of the structure of DNA by James Watson and Francis Crick in 1953 demonstrated a physical basis for inheritance.[41] Molecular biology improved our understanding of the relationship between genotype and phenotype. Advancements were also made in phylogenetic systematics, mapping the transition of traits into a comparative and testable framework through the publication and use of evolutionary trees.[42][43] In 1973, evolutionary biologist Theodosius Dobzhansky penned that “nothing in biology makes sense except in the light of evolution”, because it has brought to light the relations of what first seemed disjointed facts in natural history into a coherent explanatory body of knowledge that describes and predicts many observable facts about life on this planet.[44]

Since then, the modern synthesis has been further extended to explain biological phenomena across the full and integrative scale of the biological hierarchy, from genes to species. This extension has been dubbed “eco-evo-devo“.[45][45][46][47]


DNA structure. Bases are in the centre, surrounded by phosphate–sugar chains in a double helix.

Evolution in organisms occurs through changes in heritable traits – particular characteristics of an organism. In humans, for example, eye colour is an inherited characteristic and an individual might inherit the “brown-eye trait” from one of their parents.[48] Inherited traits are controlled by genes and the complete set of genes within an organism’s genome is called its genotype.[49]

The complete set of observable traits that make up the structure and behaviour of an organism is called its phenotype. These traits come from the interaction of its genotype with the environment.[50] As a result, many aspects of an organism’s phenotype are not inherited. For example, suntanned skin comes from the interaction between a person’s genotype and sunlight; thus, suntans are not passed on to people’s children. However, some people tan more easily than others, due to differences in their genotype; a striking example are people with the inherited trait of albinism, who do not tan at all and are very sensitive to sunburn.[51]

Heritable traits are known to be passed from one generation to the next via DNA, a molecule that encodes genetic information.[49] DNA is a long polymer composed of four types of bases. The sequence of bases along a particular DNA molecule specify the genetic information, in a manner similar to a sequence of letters spelling out a sentence. Before a cell divides, the DNA is copied, so that each of the resulting two cells will inherit the DNA sequence. Portions of a DNA molecule that specify a single functional unit are called genes; different genes have different sequences of bases. Within cells, the long strands of DNA form condensed structures called chromosomes. The specific location of a DNA sequence within a chromosome is known as a locus. If the DNA sequence at a locus varies between individuals, the different forms of this sequence are called alleles. DNA sequences can change through mutations, producing new alleles. If a mutation occurs within a gene, the new allele may affect the trait that the gene controls, altering the phenotype of the organism.[52] However, while this simple correspondence between an allele and a trait works in some cases, most traits are more complex and are controlled by multiple interacting genes.[53][54]

Recent findings have confirmed important examples of heritable changes that cannot be explained by changes to the sequence of nucleotides in the DNA. These phenomena are classed as epigenetic inheritance systems.[55] DNA methylation marking chromatin, self-sustaining metabolic loops, gene silencing by RNA interference and the three dimensional conformation of proteins (such as prions) are areas where epigenetic inheritance systems have been discovered at the organismic level.[56][57] Developmental biologists suggest that complex interactions in genetic networks and communication among cells can lead to heritable variations that may underlay some of the mechanics in developmental plasticity and canalization.[58] Heritability may also occur at even larger scales. For example, ecological inheritance through the process of niche construction is defined by the regular and repeated activities of organisms in their environment. This generates a legacy of effects that modify and feed back into the selection regime of subsequent generations. Descendants inherit genes plus environmental characteristics generated by the ecological actions of ancestors.[59] Other examples of heritability in evolution that are not under the direct control of genes include the inheritance of cultural traits and symbiogenesis.[60][61]


White peppered moth

Black morph in peppered moth evolution

Further information: Genetic diversity and Population genetics

An individual organism’s phenotype results from both its genotype and the influence from the environment it has lived in. A substantial part of the variation in phenotypes in a population is caused by the differences between their genotypes.[54] The modern evolutionary synthesis defines evolution as the change over time in this genetic variation. The frequency of one particular allele will become more or less prevalent relative to other forms of that gene. Variation disappears when a new allele reaches the point of fixation — when it either disappears from the population or replaces the ancestral allele entirely.[62]

Natural selection will only cause evolution if there is enough genetic variation in a population. Before the discovery of Mendelian genetics, one common hypothesis was blending inheritance. But with blending inheritance, genetic variance would be rapidly lost, making evolution by natural selection implausible. The Hardy-Weinberg principle provides the solution to how variation is maintained in a population with Mendelian inheritance. The frequencies of alleles (variations in a gene) will remain constant in the absence of selection, mutation, migration and genetic drift.[63]

Variation comes from mutations in genetic material, reshuffling of genes through sexual reproduction and migration between populations (gene flow). Despite the constant introduction of new variation through mutation and gene flow, most of the genome of a species is identical in all individuals of that species.[64] However, even relatively small differences in genotype can lead to dramatic differences in phenotype: for example, chimpanzees and humans differ in only about 5% of their genomes.[65]


Duplication of part of a chromosome.

Mutations are changes in the DNA sequence of a cell’s genome. When mutations occur, they can either have no effect, alter the product of a gene, or prevent the gene from functioning. Based on studies in the fly Drosophila melanogaster, it has been suggested that if a mutation changes a protein produced by a gene, this will probably be harmful, with about 70% of these mutations having damaging effects, and the remainder being either neutral or weakly beneficial.[66]

Mutations can involve large sections of a chromosome becoming duplicated (usually by genetic recombination), which can introduce extra copies of a gene into a genome.[67] Extra copies of genes are a major source of the raw material needed for new genes to evolve.[68] This is important because most new genes evolve within gene families from pre-existing genes that share common ancestors.[69] For example, the human eye uses four genes to make structures that sense light: three for colour vision and one for night vision; all four are descended from a single ancestral gene.[70]

New genes can be generated from an ancestral gene when a duplicate copy mutates and acquires a new function. This process is easier once a gene has been duplicated because it increases the redundancy of the system; one gene in the pair can acquire a new function while the other copy continues to perform its original function.[71][72] Other types of mutations can even generate entirely new genes from previously noncoding DNA.[73][74]

The generation of new genes can also involve small parts of several genes being duplicated, with these fragments then recombining to form new combinations with new functions.[75][76] When new genes are assembled from shuffling pre-existing parts, domains act as modules with simple independent functions, which can be mixed together to produce new combinations with new and complex functions.[77] For example, polyketide synthases are large enzymes that make antibiotics; they contain up to one hundred independent domains that each catalyze one step in the overall process, like a step in an assembly line.[78]

Sex and recombination

In asexual organisms, genes are inherited together, or linked, as they cannot mix with genes of other organisms during reproduction. In contrast, the offspring of sexual organisms contain random mixtures of their parents’ chromosomes that are produced through independent assortment. In a related process called homologous recombination, sexual organisms exchange DNA between two matching chromosomes.[79] Recombination and re-assortment do not alter allele frequencies, but instead change which alleles are associated with each other, producing offspring with new combinations of alleles.[80] Sex usually increases genetic variation and may increase the rate of evolution.[81][82]

Gene flow

Gene flow is the exchange of genes between populations and between species.[83] It can therefore be a source of variation that is new to a population or to a species. Gene flow can be caused by the movement of individuals between separate populations of organisms, as might be caused by the movement of mice between inland and coastal populations, or the movement of pollen between heavy metal tolerant and heavy metal sensitive populations of grasses.

Gene transfer between species includes the formation of hybrid organisms and horizontal gene transfer. Horizontal gene transfer is the transfer of genetic material from one organism to another organism that is not its offspring; this is most common among bacteria.[84] In medicine, this contributes to the spread of antibiotic resistance, as when one bacteria acquires resistance genes it can rapidly transfer them to other species.[85] Horizontal transfer of genes from bacteria to eukaryotes such as the yeast Saccharomyces cerevisiae and the adzuki bean beetle Callosobruchus chinensis has occurred.[86][87] An example of larger-scale transfers are the eukaryotic bdelloid rotifers, which have received a range of genes from bacteria, fungi and plants.[88] Viruses can also carry DNA between organisms, allowing transfer of genes even across biological domains.[89]

Large-scale gene transfer has also occurred between the ancestors of eukaryotic cells and bacteria, during the acquisition of chloroplasts and mitochondria. It is possible that eukaryotes themselves originated from horizontal gene transfers between bacteria and archaea.[90]


Mutation followed by natural selection, results in a population with darker colouration.

From a Neo-Darwinian perspective, evolution occurs when there are changes in the frequencies of alleles within a population of interbreeding organisms.[63] For example, the allele for black colour in a population of moths becoming more common. Mechanisms that can lead to changes in allele frequencies include natural selection, genetic drift, genetic hitchhiking, mutation and gene flow.

Natural selection

Evolution by means of natural selection is the process by which genetic mutations that enhance reproduction become and remain, more common in successive generations of a population. It has often been called a “self-evident” mechanism because it necessarily follows from three simple facts:


  • Heritable variation exists within populations of organisms.
  • Organisms produce more offspring than can survive.
  • These offspring vary in their ability to survive and reproduce.


These conditions produce competition between organisms for survival and reproduction. Consequently, organisms with traits that give them an advantage over their competitors pass these advantageous traits on, while traits that do not confer an advantage are not passed on to the next generation.[91]

The central concept of natural selection is the evolutionary fitness of an organism.[92] Fitness is measured by an organism’s ability to survive and reproduce, which determines the size of its genetic contribution to the next generation.[92] However, fitness is not the same as the total number of offspring: instead fitness is indicated by the proportion of subsequent generations that carry an organism’s genes.[93] For example, if an organism could survive well and reproduce rapidly, but its offspring were all too small and weak to survive, this organism would make little genetic contribution to future generations and would thus have low fitness.[92]

If an allele increases fitness more than the other alleles of that gene, then with each generation this allele will become more common within the population. These traits are said to be “selected for“. Examples of traits that can increase fitness are enhanced survival and increased fecundity. Conversely, the lower fitness caused by having a less beneficial or deleterious allele results in this allele becoming rarer — they are “selected against“.[94] Importantly, the fitness of an allele is not a fixed characteristic; if the environment changes, previously neutral or harmful traits may become beneficial and previously beneficial traits become harmful.[52] However, even if the direction of selection does reverse in this way, traits that were lost in the past may not re-evolve in an identical form (see Dollo’s law).[95][96]

A chart showing three types of selection. 1. Disruptive selection 2. Stabilizing selection 3. Directional selection

Natural selection within a population for a trait that can vary across a range of values, such as height, can be categorised into three different types. The first is directional selection, which is a shift in the average value of a trait over time — for example, organisms slowly getting taller.[97] Secondly, disruptive selection is selection for extreme trait values and often results in two different values becoming most common, with selection against the average value. This would be when either short or tall organisms had an advantage, but not those of medium height. Finally, in stabilizing selection there is selection against extreme trait values on both ends, which causes a decrease in variance around the average value and less diversity.[91][98] This would, for example, cause organisms to slowly become all the same height.

A special case of natural selection is sexual selection, which is selection for any trait that increases mating success by increasing the attractiveness of an organism to potential mates.[99] Traits that evolved through sexual selection are particularly prominent in males of some animal species, despite traits such as cumbersome antlers, mating calls or bright colours that attract predators, decreasing the survival of individual males.[100] This survival disadvantage is balanced by higher reproductive success in males that show these hard to fake, sexually selected traits.[101]

Natural selection most generally makes nature the measure against which individuals and individual traits, are more or less likely to survive. “Nature” in this sense refers to an ecosystem, that is, a system in which organisms interact with every other element, physical as well as biological, in their local environment. Eugene Odum, a founder of ecology, defined an ecosystem as: “Any unit that includes all of the organisms…in a given area interacting with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity and material cycles (ie: exchange of materials between living and nonliving parts) within the system.”[102] Each population within an ecosystem occupies a distinct niche, or position, with distinct relationships to other parts of the system. These relationships involve the life history of the organism, its position in the food chain and its geographic range. This broad understanding of nature enables scientists to delineate specific forces which, together, comprise natural selection.

Natural selection can act at different levels of organisation, such as genes, cells, individual organisms, groups of organisms and species.[103][104][105] Selection can act at multiple levels simultaneously.[106] An example of selection occurring below the level of the individual organism are genes called transposons, which can replicate and spread throughout a genome.[107] Selection at a level above the individual, such as group selection, may allow the evolution of co-operation, as discussed below.[108]

Biased mutation

In addition to being a major source of variation, mutation may also function as a mechanism of evolution when there are different probabilities at the molecular level for different mutations to occur, a process known as mutation bias.[109] If two genotypes, for example one with the nucleotide G and another with the nucleotide A in the same position, have the same fitness, but mutation from G to A happens more often than mutation from A to G, then genotypes with A will tend to evolve.[110] Different insertion vs. deletion mutation biases in different taxa can lead to the evolution of different genome sizes.[111][112] Developmental or mutational biases have also been observed in morphological evolution.[113][114] For example, according to the phenotype-first theory of evolution, mutations can eventually cause the genetic assimilation of traits that were previously induced by the environment.[115][116]

Mutation bias effects are superimposed on other processes. If selection would favor either one out of two mutations, but there is no extra advantage to having both, then the mutation that occurs the most frequently is the one that is most likely to become fixed in a population.[117][118] Mutations leading to the loss of function of a gene are much more common than mutations that produce a new, fully functional gene. Most loss of function mutations are selected against. But when selection is weak, mutation bias towards loss of function can affect evolution.[119] For example, pigments are no longer useful when animals live in the darkness of caves, and tend to be lost.[120] This kind of loss of function can occur because of mutation bias, and/or because the function had a cost, and once the benefit of the function disappeared, natural selection leads to the loss. Loss of sporulation ability in a bacterium during laboratory evolution appears to have been caused by mutation bias, rather than natural selection against the cost of maintaining sporulation ability.[121] When there is no selection for loss of function, the speed at which loss evolves depends more on the mutation rate than it does on the effective population size,[122] indicating that it is driven more by mutation bias than by genetic drift.

Genetic drift

Simulation of genetic drift of 20 unlinked alleles in populations of 10 (top) and 100 (bottom). Drift to fixation is more rapid in the smaller population.

Genetic drift is the change in allele frequency from one generation to the next that occurs because alleles are subject to sampling error.[123] As a result, when selective forces are absent or relatively weak, allele frequencies tend to “drift” upward or downward randomly (in a random walk). This drift halts when an allele eventually becomes fixed, either by disappearing from the population, or replacing the other alleles entirely. Genetic drift may therefore eliminate some alleles from a population due to chance alone. Even in the absence of selective forces, genetic drift can cause two separate populations that began with the same genetic structure to drift apart into two divergent populations with different sets of alleles.[124]

It is usually difficult to measure the relative importance of selection and neutral processes, including drift.[125] The comparative importance of adaptive and non-adaptive forces in driving evolutionary change is an area of current research.[126]

The neutral theory of molecular evolution proposed that most evolutionary changes are the result of the fixation of neutral mutations by genetic drift.[5] Hence, in this model, most genetic changes in a population are the result of constant mutation pressure and genetic drift.[127] This form of the neutral theory is now largely abandoned, since it does not seem to fit the genetic variation seen in nature.[128][129] However, a more recent and better-supported version of this model is the nearly neutral theory, where a mutation that would be neutral in a small population is not necessarily neutral in a large population.[91] Other alternative theories propose that genetic drift is dwarfed by other stochastic forces in evolution, such as genetic hitchhiking, also known as genetic draft.[123][130][131]

The time for a neutral allele to become fixed by genetic drift depends on population size, with fixation occurring more rapidly in smaller populations.[132] The number of individuals in a population is not critical, but instead a measure known as the effective population size.[133] The effective population is usually smaller than the total population since it takes into account factors such as the level of inbreeding and the stage of the lifecycle in which the population is the smallest.[133] The effective population size may not be the same for every gene in the same population.[134]

Genetic hitchhiking

Recombination allows alleles on the same strand of DNA to become separated. However, the rate of recombination is low (approximately two events per chromosome per generation). As a result, genes close together on a chromosome may not always be shuffled away from each other and genes that are close together tend to be inherited together, a phenomenon known as linkage.[135] This tendency is measured by finding how often two alleles occur together on a single chromosome compared to expectations, which is called their linkage disequilibrium. A set of alleles that is usually inherited in a group is called a haplotype. This can be important when one allele in a particular haplotype is strongly beneficial: natural selection can drive a selective sweep that will also cause the other alleles in the haplotype to become more common in the population; this effect is called genetic hitchhiking or genetic draft.[136] Genetic draft caused by the fact that some neutral genes are genetically linked to others that are under selection can be partially captured by an appropriate effective population size.[130]

Gene flow

Gene flow is the exchange of genes between populations and between species.[83] The presence or absence of gene flow fundamentally changes the course of evolution. Due to the complexity of organisms, any two completely isolated populations will eventually evolve genetic incompatibilities through neutral processes, as in the Bateson-Dobzhansky-Muller model, even if both populations remain essentially identical in terms of their adaptation to the environment.

If genetic differentiation between populations develops, gene flow between populations can introduce traits or alleles which are disadvantageous in the local population and this may lead to organism within these populations to evolve mechanisms that prevent mating with genetically distant populations, eventually resulting in the appearance of new species. Thus, exchange of genetic information between individuals is fundamentally important for the development of the biological species concept (BSC).

During the development of the modern synthesis, Sewall Wright‘s developed his shifting balance theory that gene flow between partially isolated populations was an important aspect of adaptive evolution.[137] However, recently there has been substantial criticism of the importance of the shifting balance theory.[138]


Evolution influences every aspect of the form and behaviour of organisms. Most prominent are the specific behavioural and physical adaptations that are the outcome of natural selection. These adaptations increase fitness by aiding activities such as finding food, avoiding predators or attracting mates. Organisms can also respond to selection by co-operating with each other, usually by aiding their relatives or engaging in mutually beneficial symbiosis. In the longer term, evolution produces new species through splitting ancestral populations of organisms into new groups that cannot or will not interbreed.

These outcomes of evolution are sometimes divided into macroevolution, which is evolution that occurs at or above the level of species, such as extinction and speciation and microevolution, which is smaller evolutionary changes, such as adaptations, within a species or population.[139] In general, macroevolution is regarded as the outcome of long periods of microevolution.[140] Thus, the distinction between micro- and macroevolution is not a fundamental one – the difference is simply the time involved.[141] However, in macroevolution, the traits of the entire species may be important. For instance, a large amount of variation among individuals allows a species to rapidly adapt to new habitats, lessening the chance of it going extinct, while a wide geographic range increases the chance of speciation, by making it more likely that part of the population will become isolated. In this sense, microevolution and macroevolution might involve selection at different levels – with microevolution acting on genes and organisms, versus macro-evolutionary processes such as species selection acting on entire species and affecting their rates of speciation and extinction.[142][143][144]

A common misconception is that evolution has goals or long-term plans; realistically however, evolution has no long-term goal and does not necessarily produce greater complexity.[145][146] Although complex species have evolved, they occur as a side effect of the overall number of organisms increasing and simple forms of life still remain more common in the biosphere.[147] For example, the overwhelming majority of species are microscopic prokaryotes, which form about half the world’s biomass despite their small size,[148] and constitute the vast majority of Earth’s biodiversity.[149] Simple organisms have therefore been the dominant form of life on Earth throughout its history and continue to be the main form of life up to the present day, with complex life only appearing more diverse because it is more noticeable.[150] Indeed, the evolution of microorganisms is particularly important to modern evolutionary research, since their rapid reproduction allows the study of experimental evolution and the observation of evolution and adaptation in real time.[151][152]


Adaptation is the process that makes organisms better suited to their habitat.[153][154] Also, the term adaptation may refer to a trait that is important for an organism’s survival. For example, the adaptation of horses’ teeth to the grinding of grass. By using the term adaptation for the evolutionary process and adaptive trait for the product (the bodily part or function), the two senses of the word may be distinguished. Adaptations are produced by natural selection.[155] The following definitions are due to Theodosius Dobzhansky.

  1. Adaptation is the evolutionary process whereby an organism becomes better able to live in its habitat or habitats.[156]
  2. Adaptedness is the state of being adapted: the degree to which an organism is able to live and reproduce in a given set of habitats.[157]
  3. An adaptive trait is an aspect of the developmental pattern of the organism which enables or enhances the probability of that organism surviving and reproducing.[158]

Adaptation may cause either the gain of a new feature, or the loss of an ancestral feature. An example that shows both types of change is bacterial adaptation to antibiotic selection, with genetic changes causing antibiotic resistance by both modifying the target of the drug, or increasing the activity of transporters that pump the drug out of the cell.[159] Other striking examples are the bacteria Escherichia coli evolving the ability to use citric acid as a nutrient in a long-term laboratory experiment,[160] Flavobacterium evolving a novel enzyme that allows these bacteria to grow on the by-products of nylon manufacturing,[161][162] and the soil bacterium Sphingobium evolving an entirely new metabolic pathway that degrades the synthetic pesticide pentachlorophenol.[163][164] An interesting but still controversial idea is that some adaptations might increase the ability of organisms to generate genetic diversity and adapt by natural selection (increasing organisms’ evolvability).[165][166][167][168]

A baleen whale skeleton, a and b label flipper bones, which were adapted from front leg bones: while c indicates vestigial leg bones, suggesting an adaptation from land to sea.[169]

Adaptation occurs through the gradual modification of existing structures. Consequently, structures with similar internal organisation may have different functions in related organisms. This is the result of a single ancestral structure being adapted to function in different ways. The bones within bat wings, for example, are very similar to those in mice feet and primate hands, due to the descent of all these structures from a common mammalian ancestor.[170] However, since all living organisms are related to some extent,[171] even organs that appear to have little or no structural similarity, such as arthropod, squid and vertebrate eyes, or the limbs and wings of arthropods and vertebrates, can depend on a common set of homologous genes that control their assembly and function; this is called deep homology.[172][173]

During evolution, some structures may lose their original function and become vestigial structures.[174] Such structures may have little or no function in a current species, yet have a clear function in ancestral species, or other closely related species. Examples include pseudogenes,[175] the non-functional remains of eyes in blind cave-dwelling fish,[176] wings in flightless birds,[177] and the presence of hip bones in whales and snakes.[169] Examples of vestigial structures in humans include wisdom teeth,[178] the coccyx,[174] the vermiform appendix,[174] and other behavioural vestiges such as goose bumps[179][180] and primitive reflexes.[181][182][183]

However, many traits that appear to be simple adaptations are in fact exaptations: structures originally adapted for one function, but which coincidentally became somewhat useful for some other function in the process.[184] One example is the African lizard Holaspis guentheri, which developed an extremely flat head for hiding in crevices, as can be seen by looking at its near relatives. However, in this species, the head has become so flattened that it assists in gliding from tree to tree—an exaptation.[184] Within cells, molecular machines such as the bacterial flagella[185] and protein sorting machinery[186] evolved by the recruitment of several pre-existing proteins that previously had different functions.[139] Another example is the recruitment of enzymes from glycolysis and xenobiotic metabolism to serve as structural proteins called crystallins within the lenses of organisms’ eyes.[187][188]

A critical principle of ecology is that of competitive exclusion: no two species can occupy the same niche in the same environment for a long time.[189] Consequently, natural selection will tend to force species to adapt to different ecological niches. This may mean that, for example, two species of cichlid fish adapt to live in different habitats, which will minimise the competition between them for food.[190]

An area of current investigation in evolutionary developmental biology is the developmental basis of adaptations and exaptations.[191] This research addresses the origin and evolution of embryonic development and how modifications of development and developmental processes produce novel features.[192] These studies have shown that evolution can alter development to produce new structures, such as embryonic bone structures that develop into the jaw in other animals instead forming part of the middle ear in mammals.[193] It is also possible for structures that have been lost in evolution to reappear due to changes in developmental genes, such as a mutation in chickens causing embryos to grow teeth similar to those of crocodiles.[194] It is now becoming clear that most alterations in the form of organisms are due to changes in a small set of conserved genes.[195]


Common Garter Snake (Thamnophis sirtalis sirtalis) which has evolved resistance to tetrodotoxin in its amphibian prey.

Interactions between organisms can produce both conflict and co-operation. When the interaction is between pairs of species, such as a pathogen and a host, or a predator and its prey, these species can develop matched sets of adaptations. Here, the evolution of one species causes adaptations in a second species. These changes in the second species then, in turn, cause new adaptations in the first species. This cycle of selection and response is called co-evolution.[196] An example is the production of tetrodotoxin in the rough-skinned newt and the evolution of tetrodotoxin resistance in its predator, the common garter snake. In this predator-prey pair, an evolutionary arms race has produced high levels of toxin in the newt and correspondingly high levels of toxin resistance in the snake.[197]


Not all co-evolved interactions between species involve conflict.[198] Many cases of mutually beneficial interactions have evolved. For instance, an extreme cooperation exists between plants and the mycorrhizal fungi that grow on their roots and aid the plant in absorbing nutrients from the soil.[199] This is a reciprocal relationship as the plants provide the fungi with sugars from photosynthesis. Here, the fungi actually grow inside plant cells, allowing them to exchange nutrients with their hosts, while sending signals that suppress the plant immune system.[200]

Coalitions between organisms of the same species have also evolved. An extreme case is the eusociality found in social insects, such as bees, termites and ants, where sterile insects feed and guard the small number of organisms in a colony that are able to reproduce. On an even smaller scale, the somatic cells that make up the body of an animal limit their reproduction so they can maintain a stable organism, which then supports a small number of the animal’s germ cells to produce offspring. Here, somatic cells respond to specific signals that instruct them whether to grow, remain as they are, or die. If cells ignore these signals and multiply inappropriately, their uncontrolled growth causes cancer.[201]

Such cooperation within species may have evolved through the process of kin selection, which is where one organism acts to help raise a relative’s offspring.[202] This activity is selected for because if the helping individual contains alleles which promote the helping activity, it is likely that its kin will also contain these alleles and thus those alleles will be passed on.[203] Other processes that may promote cooperation include group selection, where cooperation provides benefits to a group of organisms.[204]


The four mechanisms of speciation.

Speciation is the process where a species diverges into two or more descendant species.[205]

There are multiple ways to define the concept of “species”. The choice of definition is dependent on the particularities of the species concerned.[206] For example, some species concepts apply more readily toward sexually reproducing organisms while others lend themselves better toward asexual organisms. Despite the diversity of various species concepts, these various concepts can be placed into one of three broad philosophical approaches: interbreeding, ecological and phylogenetic.[207] The biological species concept (BSC) is a classic example of the interbreeding approach. Defined by Ernst Mayr in 1942, the BSC states that “species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups”[208]:120. Despite its wide and long-term use, the BSC like others is not without controversy, for example because these concepts cannot be applied to prokaryotes,[209] and this is called the species problem.[206] Some researchers have attempted a unifying monistic definition of species, while others adopt a pluralistic approach and suggest that there may be a different ways to logically interpret the definition of a species.[206][207]

Barriers to reproduction between two diverging sexual populations are required for the populations to become new species. Gene flow may slow this process by spreading the new genetic variants also to the other populations. Depending on how far two species have diverged since their most recent common ancestor, it may still be possible for them to produce offspring, as with horses and donkeys mating to produce mules.[210] Such hybrids are generally infertile. In this case, closely related species may regularly interbreed, but hybrids will be selected against and the species will remain distinct. However, viable hybrids are occasionally formed and these new species can either have properties intermediate between their parent species, or possess a totally new phenotype.[211] The importance of hybridisation in producing new species of animals is unclear, although cases have been seen in many types of animals,[212] with the gray tree frog being a particularly well-studied example.[213]

Speciation has been observed multiple times under both controlled laboratory conditions and in nature.[214] In sexually reproducing organisms, speciation results from reproductive isolation followed by genealogical divergence. There are four mechanisms for speciation. The most common in animals is allopatric speciation, which occurs in populations initially isolated geographically, such as by habitat fragmentation or migration. Selection under these conditions can produce very rapid changes in the appearance and behaviour of organisms.[215][216] As selection and drift act independently on populations isolated from the rest of their species, separation may eventually produce organisms that cannot interbreed.[217]

The second mechanism of speciation is peripatric speciation, which occurs when small populations of organisms become isolated in a new environment. This differs from allopatric speciation in that the isolated populations are numerically much smaller than the parental population. Here, the founder effect causes rapid speciation after an increase in inbreeding increases selection on homozygotes, leading to rapid genetic change.[218]

The third mechanism of speciation is parapatric speciation. This is similar to peripatric speciation in that a small population enters a new habitat, but differs in that there is no physical separation between these two populations. Instead, speciation results from the evolution of mechanisms that reduce gene flow between the two populations.[205] Generally this occurs when there has been a drastic change in the environment within the parental species’ habitat. One example is the grass Anthoxanthum odoratum, which can undergo parapatric speciation in response to localised metal pollution from mines.[219] Here, plants evolve that have resistance to high levels of metals in the soil. Selection against interbreeding with the metal-sensitive parental population produced a gradual change in the flowering time of the metal-resistant plants, which eventually produced complete reproductive isolation. Selection against hybrids between the two populations may cause reinforcement, which is the evolution of traits that promote mating within a species, as well as character displacement, which is when two species become more distinct in appearance.[220]

Geographical isolation of finches on the Galápagos Islands produced over a dozen new species.

Finally, in sympatric speciation species diverge without geographic isolation or changes in habitat. This form is rare since even a small amount of gene flow may remove genetic differences between parts of a population.[221] Generally, sympatric speciation in animals requires the evolution of both genetic differences and non-random mating, to allow reproductive isolation to evolve.[222]

One type of sympatric speciation involves cross-breeding of two related species to produce a new hybrid species. This is not common in animals as animal hybrids are usually sterile. This is because during meiosis the homologous chromosomes from each parent are from different species and cannot successfully pair. However, it is more common in plants because plants often double their number of chromosomes, to form polyploids.[223] This allows the chromosomes from each parental species to form matching pairs during meiosis, since each parent’s chromosomes are represented by a pair already.[224] An example of such a speciation event is when the plant species Arabidopsis thaliana and Arabidopsis arenosa cross-bred to give the new species Arabidopsis suecica.[225] This happened about 20,000 years ago,[226] and the speciation process has been repeated in the laboratory, which allows the study of the genetic mechanisms involved in this process.[227] Indeed, chromosome doubling within a species may be a common cause of reproductive isolation, as half the doubled chromosomes will be unmatched when breeding with undoubled organisms.[228]

Speciation events are important in the theory of punctuated equilibrium, which accounts for the pattern in the fossil record of short “bursts” of evolution interspersed with relatively long periods of stasis, where species remain relatively unchanged.[229] In this theory, speciation and rapid evolution are linked, with natural selection and genetic drift acting most strongly on organisms undergoing speciation in novel habitats or small populations. As a result, the periods of stasis in the fossil record correspond to the parental population and the organisms undergoing speciation and rapid evolution are found in small populations or geographically restricted habitats and therefore rarely being preserved as fossils.[230]


Tyrannosaurus rex. Non-avian dinosaurs died out in the Cretaceous–Tertiary extinction event at the end of the Cretaceous period.

Extinction is the disappearance of an entire species. Extinction is not an unusual event, as species regularly appear through speciation and disappear through extinction.[231] Nearly all animal and plant species that have lived on Earth are now extinct,[232] and extinction appears to be the ultimate fate of all species.[233] These extinctions have happened continuously throughout the history of life, although the rate of extinction spikes in occasional mass extinction events.[234] The Cretaceous–Tertiary extinction event, during which the non-avian dinosaurs went extinct, is the most well-known, but the earlier Permian–Triassic extinction event was even more severe, with approximately 96% of species driven to extinction.[234] The Holocene extinction event is an ongoing mass extinction associated with humanity’s expansion across the globe over the past few thousand years. Present-day extinction rates are 100–1000 times greater than the background rate and up to 30% of species may be extinct by the mid 21st century.[235] Human activities are now the primary cause of the ongoing extinction event;[236] global warming may further accelerate it in the future.[237]

The role of extinction in evolution is not very well understood and may depend on which type of extinction is considered.[234] The causes of the continuous “low-level” extinction events, which form the majority of extinctions, may be the result of competition between species for limited resources (competitive exclusion).[45] If one species can out-compete another, this could produce species selection, with the fitter species surviving and the other species being driven to extinction.[104] The intermittent mass extinctions are also important, but instead of acting as a selective force, they drastically reduce diversity in a nonspecific manner and promote bursts of rapid evolution and speciation in survivors.[238]

Evolutionary History of Life

Origin of life

Highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago and half a billion years later the last common ancestor of all life existed.[239] The current scientific consensus is that the complex biochemistry that makes up life came from simpler chemical reactions.[240] The beginning of life may have included self-replicating molecules such as RNA,[241] and the assembly of simple cells.[242]

Common descent

The hominoids are descendants of a common ancestor.

All organisms on Earth are descended from a common ancestor or ancestral gene pool.[171][243] Current species are a stage in the process of evolution, with their diversity the product of a long series of speciation and extinction events.[244] The common descent of organisms was first deduced from four simple facts about organisms: First, they have geographic distributions that cannot be explained by local adaptation. Second, the diversity of life is not a set of completely unique organisms, but organisms that share morphological similarities. Third, vestigial traits with no clear purpose resemble functional ancestral traits and finally, that organisms can be classified using these similarities into a hierarchy of nested groups – similar to a family tree.[245] However, modern research has suggested that, due to horizontal gene transfer, this “tree of life” may be more complicated than a simple branching tree since some genes have spread independently between distantly related species.[246][247]

Past species have also left records of their evolutionary history. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record.[248] By comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. However, this approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. Further, as prokaryotes such as bacteria and archaea share a limited set of common morphologies, their fossils do not provide information on their ancestry.

More recently, evidence for common descent has come from the study of biochemical similarities between organisms. For example, all living cells use the same basic set of nucleotides and amino acids.[249] The development of molecular genetics has revealed the record of evolution left in organisms’ genomes: dating when species diverged through the molecular clock produced by mutations.[250] For example, these DNA sequence comparisons have revealed that humans and chimpanzees share 96% of their genomes and analyzing the few areas where they differ helps shed light on when the common ancestor of these species existed.[251]

Evolution of life

Evolutionary tree showing the divergence of modern species from their common ancestor in the centre.[252] The three domains are coloured, with bacteria blue, archaea green and eukaryotes red.

Prokaryotes inhabited the Earth from approximately 3–4 billion years ago.[253][254] No obvious changes in morphology or cellular organisation occurred in these organisms over the next few billion years.[255] The eukaryotic cells emerged between 1.6 – 2.7 billion years ago. The next major change in cell structure came when bacteria were engulfed by eukaryotic cells, in a cooperative association called endosymbiosis.[256][257] The engulfed bacteria and the host cell then underwent co-evolution, with the bacteria evolving into either mitochondria or hydrogenosomes.[258] Another engulfment of cyanobacterial-like organisms led to the formation of chloroplasts in algae and plants.[259]

The history of life was that of the unicellular eukaryotes, prokaryotes and archaea until about 610 million years ago when multicellular organisms began to appear in the oceans in the Ediacaran period.[253][260] The evolution of multicellularity occurred in multiple independent events, in organisms as diverse as sponges, brown algae, cyanobacteria, slime moulds and myxobacteria.[261]

Soon after the emergence of these first multicellular organisms, a remarkable amount of biological diversity appeared over approximately 10 million years, in an event called the Cambrian explosion. Here, the majority of types of modern animals appeared in the fossil record, as well as unique lineages that subsequently became extinct.[262] Various triggers for the Cambrian explosion have been proposed, including the accumulation of oxygen in the atmosphere from photosynthesis.[263]

About 500 million years ago, plants and fungi colonised the land and were soon followed by arthropods and other animals.[264] Insects were particularly successful and even today make up the majority of animal species.[265] Amphibians first appeared around 364 million years ago, followed by early amniotes, then birds around 155 million years ago (both from “reptile“-like lineages), mammals around 129 million years ago, homininae around 10 million years ago and modern humans around 0.25 million years ago.[266][267][268] However, despite the evolution of these large animals, smaller organisms similar to the types that evolved early in this process continue to be highly successful and dominate the Earth, with the majority of both biomass and species being prokaryotes.[149]


Concepts and models used in evolutionary biology, in particular natural selection, have many applications.[269]

Artificial selection is the intentional selection of traits in a population of organisms. This has been used for thousands of years in the domestication of plants and animals.[270] More recently, such selection has become a vital part of genetic engineering, with selectable markers such as antibiotic resistance genes being used to manipulate DNA. In repeated rounds of mutation and selection proteins with valuable properties have evolved, for example modified enzymes and new antibodies, in a process called directed evolution.[271]

Understanding the changes that have occurred during organism’s evolution can reveal the genes needed to construct parts of the body, genes which may be involved in human genetic disorders.[272] For example, the mexican tetra is an albino cavefish that lost its eyesight during evolution. Breeding together different populations of this blind fish produced some offspring with functional eyes, since different mutations had occurred in the isolated populations that had evolved in different caves.[273] This helped identify genes required for vision and pigmentation.[274]

In computer science, simulations of evolution using evolutionary algorithms and artificial life started in the 1960s and was extended with simulation of artificial selection.[275] Artificial evolution became a widely recognised optimisation method as a result of the work of Ingo Rechenberg in the 1960s. He used evolution strategies to solve complex engineering problems.[276] Genetic algorithms in particular became popular through the writing of John Holland.[277] Practical applications also include automatic evolution of computer programs.[278] Evolutionary algorithms are now used to solve multi-dimensional problems more efficiently than software produced by human designers and also to optimise the design of systems.[279]

Social and Cultural Responses

As evolution became widely accepted in the 1870s, caricatures of Charles Darwin with an ape or monkey body symbolised evolution.[280]

In the 19th century, particularly after the publication of On the Origin of Species in 1859, the idea that life had evolved was an active source of academic debate centred on the philosophical, social and religious implications of evolution. Today, the modern evolutionary synthesis is accepted by a vast majority of scientists.[45] However, evolution remains a contentious concept for some theists.[281]

While various religions and denominations have reconciled their beliefs with evolution through concepts such as theistic evolution, there are creationists who believe that evolution is contradicted by the creation myths found in their religions and who raise various objections to evolution.[139][282][283] As had been demonstrated by responses to the publication of Vestiges of the Natural History of Creation in 1844, the most controversial aspect of evolutionary biology is the implication of human evolution that humans share common ancestry with apes and that the mental and moral faculties of humanity have the same types of natural causes as other inherited traits in animals.[284] In some countries, notably the United States, these tensions between science and religion have fuelled the current creation-evolution controversy, a religious conflict focusing on politics and public education.[285] While other scientific fields such as cosmology[286] and Earth science[287] also conflict with literal interpretations of many religious texts, evolutionary biology experiences significantly more opposition from religious literalists.

The teaching of evolution in American secondary school biology classes was uncommon in most of the first half of the 20th century. The Scopes Trial decision of 1925 caused the subject to become very rare in American secondary biology textbooks for a generation, but it was gradually re-introduced about a generation later and legally protected with the 1968 Epperson v. Arkansas decision. Since then, the competing religious belief of creationism was legally disallowed in secondary school curricula in various decisions in the 1970s and 1980s, but it returned in pseudoscientific form as intelligent design, to be excluded once again in the 2005 Kitzmiller v. Dover Area School District case.[288]


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Evolution as Fact and Theory

Casting evolution as fact and theory occurs regularly in the public and scientific discourse on the fundamental nature of the scientific philosophy within evolutionary biology. This topic appears frequently in publications that aim to clarify misconceptions about the science of evolution and the nature of these terms, often in response to creationist claims that “evolution is only a theory”, “it is not a fact”, or that intelligent design offers a credible counter “theory”. In ensuing debates, evolution is identified as either fact or theory and occasionally both or neither. Semantic differences between the usage of these terms (fact and theory) in science versus the meanings they convey in common vernacular have led to confusion in public discourse. In the context of creationists claims, theory is used in its vernacular meaning as an imperfect fact or an unsubstantiated speculation. The purported intent is to discredit or reject the scientific credibility of evolution. However, this claim cannot be substantiated.[1][2][3]

Evolutionary theory unifies observations from fossils, DNA sequences, systematics, biogeography, and laboratory experiments into a testable explanatory scheme. In this sense, the scientific (as opposed to the vernacular) definition of theory refers to an overarching framework that makes sense of otherwise disconnected observations; this includes, for example, the theory of gravity. Theodosius Dobzhansky, a key contributor to the modern evolutionary synthesis, articulated the unifying power of evolutionary theory in a famous paper entitled: “Nothing in biology makes sense except in the light of evolution“.[4]

The scientific theory of evolution explains the causes of evolution, as distinct from the more straightforward factual claim that the process of evolution occurs. Natural selection and the neutral theory are examples of theories of evolution. These and many other causal evolutionary theories can be expressed in the mathematical framework of population genetics. Since Darwin, the theory of evolution by means of natural selection has not only been expressed mathematically, but has also been rigorously tested and corroborated empirically by scientific evidence from countless studies. Evolutionary theories continue to generate new testable hypotheses within paleontology, genetics, ecology, and developmental biology.

A fact is not a statement of certainty, but through repeated confirmation the things or processes they refer to are generally accepted as true according to the reliability of inference (inductive, deductive, and abductive). Facts refer to “events that occur” or “the state of being of things” that can be publicly verified, proven through experiment, or witnessed by direct observation.[3][5] That all forms of life on Earth are related by common descent with modification is one of the most reliable and empirically tested theories in science that continues to explain vast numbers of facts in biology.[2]

Evolution, Fact and Theory

The early developmental stages of most sciences have been characterized by continual competition between a number of distinct views of nature, each partially derived from, and all roughly compatible with, the dictates of scientific observation and method.[6]:4

Evolution has been described as “fact and theory”, “fact not theory”, “only a theory, not a fact”, and “multiple theories, not fact”. Science cannot achieve absolute “certainty” nor is it a continuous march toward an objective truth as the vernacular meaning of the terms “proof” or “fact” might imply. A proof, fact, theory, hypothesis, and other words of science are hobbled by multiple meanings but are used nonetheless because they invigorate research methods and lead to discovery in all branches of scientific research. The philosophy of scientific inquiry solves problems of novelty as discoveries are made. Scientific knowledge is shared, incorporated, and tested across disciplines.[3][7][6][8] Charles Darwin, for example, not only advanced theory and hypotheses in evolution, but experimented and tested his ideas across disciplines, including and not limited to geology, botany, psychology, and ecology.[9]

“…scientific knowledge is tentative (subject to change); empirically based (based on and/or derived from observations of the natural world); subjective (theory-laden); partly the product of human inference, imagination, and creativity (involves the invention of explanation); and socially and culturally embedded…Although there is overlap and interaction between science processes and the nature of science, it is nevertheless important to distinguish the two.”[10] :418

Evolutionary science is part of larger network of scientific theory that is used to confront and deal with the world. Science is a collective enterprise that may redefine its theories via the process of experimentation. By necessity, scientific ideas begin as speculation, because scientists lack foresight on correct solutions as they push the boundaries of knowledge and discovery. Scientific research has been called the “…interplay between imagination (hypothesis formulation) and experiment.”[9]:10035 In the process, scientists gather facts, conduct experiments, analyze, probe, prod, scrutinize, communicate on, and raise questions about the natural world. Over time, methods are developed and improved to further scientific knowledge related to the theory. Unexpected discoveries are not immediately integrated as fact. Science is developmentally enriched through the novelties of fact and theory.[3][11][6] In this context, the meanings of the terms “evolution”, “fact”, and “theory” are described below.


Evolution is generally defined as changes in trait or gene frequency in a population of organisms from one generation to the next. This has been dubbed the standard genetic definition of evolution. Other definitions of evolution cover a much broader scale overarching multiple levels of biological organisation, from macroevolutionary phenomena that occur during species formation and divergence, to microevolutionary processes within individual organisms, cells, and biomolecules such as DNA and proteins.[12][13] Evolution also refers to Darwin’s theory of natural selection, which is the only known mechanism that can lead to adaptations and is only one of multiple mechanisms of evolutionary change. Natural selection is a process that acts on the heritable characteristics of individuals that interact and reproduce to form lineages of biological populations. Genetic drift, gene flow, vicariance biogeography, and niche construction are examples of other evolutionary mechanisms.[14][15] Evolution leads to the following additional claims:

  1. Differences in trait composition between isolated populations over many generations may result in the origin of new species.
  2. All living organisms alive today have descended from a common ancestor (or ancestral gene pool).

According to Douglas Futuyma:

Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different alleles within a population (such as those determining blood types) to the successive alterations that led from the earliest proto-organism to snails, bees, giraffes, and dandelions.[16]

Evolutionary theory may also refer to cultural evolution.[13] Evolutionary science provides an overarching framework in biology for identifying relationships and providing a coherent understanding of otherwise disconnected natural observations.


Hypotheses and theories are fallible, theory-laden constructs. Such fallibility does not, however, apply to facts, since facts merely exist regardless of their being perceived. The basis for testing is to evaluate the veracity of our claims regarding facts.[3]:2

Facts are “events that occur” or “the state of being of things” that are referred too. Facts exist independent of theory. Scientists do not construct facts, but make observations about things that refer to or represent the facts through theory.[17] Unlike other terms of science, facts in science are similar in definition and interpretation relative to their use in common language.[3][18] Fact is often used by scientists to refer to experimental or empirical data or objective verifiable observations. However, scientists do not accept facts as absolute truth and in some cases even observations have been defined “as low-level hypotheses that exist only as interpretations of the facts of nature in light of present theories, not as the facts of nature themselves.”[19]:234 According to this view, all concepts are theory-laden meaning that there is always an element of subjective interpretation embedded in our language.[20] The US National Academy of Science defines a scientific fact as “an observation that has been repeatedly confirmed, and for all practical purposes, is accepted as ‘true’.”[21] Facts are also established through the process of experimentation:

A fact is a hypothesis that is so firmly supported by evidence that we assume it is true, and act as if it were true. —Douglas Futuyma[22]

Evolution is a fact in the sense that it is overwhelmingly validated by the evidence. Frequently, evolution is said to be a fact in the same way as the Earth revolving around the Sun is a fact.[22][23] The following quotation from H. J. Muller, “One Hundred Years Without Darwin Are Enough” explains the point.

There is no sharp line between speculation, hypothesis, theory, principle, and fact, but only a difference along a sliding scale, in the degree of probability of the idea. When we say a thing is a fact, then, we only mean that its probability is an extremely high one: so high that we are not bothered by doubt about it and are ready to act accordingly. Now in this use of the term fact, the only proper one, evolution is a fact.[24]

The National Academy of Science (U.S.) makes a similar point:

Scientists most often use the word “fact” to describe an observation. But scientists can also use fact to mean something that has been tested or observed so many times that there is no longer a compelling reason to keep testing or looking for examples. The occurrence of evolution in this sense is fact. Scientists no longer question whether descent with modification occurred because the evidence is so strong.[25]

Philosophers of science argue that we do not know mind-independent empirical truths with absolute certainty: even direct observations may be “theory laden” and depend on assumptions about our senses and the measuring instruments used. Reference to a fact does not mean “absolute certainty”.[26][27] According to the paleontologist Stephen Jay Gould, a “fact” in science can only mean that which is “confirmed to such a degree that it would be perverse to withhold provisional assent.”[1] Some philosophers and evolutionary biologists have noted that hypotheses that are empirically corroborated, such as descent with modification, are not in themselves facts, but they refer to processes that are facts. In this way, evolution is not in itself a fact, but the processes or mechanisms of evolution, such as natural selection, are factual and have undeniably lead to the diversified forms of life inhabiting this planet.[17][3]


The scientific definition of the word “theory” is different from the colloquial sense of the word. In the vernacular, “theory” can refer to guesswork, a simple conjecture, an opinion, or a speculation that does not have to be based on facts and need not be framed for making testable predictions. Scientific theories also contain speculation at first as scientists necessarily reach past the threshold of current knowledge, but they develop heuristically or through axillary claims as observations from experiments are explained and cause-effect relations are understood. Theories are constructs having both explanatory and predictive capacities that are built on inferential sets of logic (consilience of inductions, abductions, and deductions), models, and syllogistic schemes or laws that can be falsified through well designed experiments. In this way, theories that survive and develop through critical testing, such as Charles Darwin’s theories on evolution, become richly informative as they explain cause-effect relations among many observable phenomena.[3][11][1][28]

Theories give more general explanations of systems in nature than the hypotheses they generate. Hypotheses are explanatory statements for testing specific instances, inferences, or examples of the theory. Hypotheses make experimental claims about specific events in the past that produce effects that can be observed in the present. In contrast, theories apply universally as spatio-temporally unrestricted accounts of cause-effect relations. Theoretical models are one of many kinds of scientific methods that can used to communicate accurate and precise depictions of particular systems or organisms that are continually and repetitively investigated.[3][29][30][11][28]

The “theory of evolution” is actually a network of theories that have developed through the practice and understanding of the science involved. Charles Darwin, for example, proposed five separate theories in his original formulation, which included mechanistic explanations for: (1) populations changing over generations, (2) gradual change, (3) speciation, (4) natural selection, and (5) common descent.[13] Since Darwin, evolution has become a well-supported body of interconnected statements that explains numerous empirical observations in the natural world. Evolutionary theories continue to generate testable predictions and explanations about living and fossilized organisms.[3][11]

Evolutionary theories include theories about inheritance. Under the blending inheritance theory, evolution by natural selection is exceedingly difficult, since genetic variation is rapidly lost. A theoretical advance known as the Hardy–Weinberg principle shows that, under the alternative inheritance theory of Mendelian genetics, variation is not easily lost. The Hardy-Weinberg genotype frequencies also facilitate the population genetics study of natural selection using diploid replicator equations.[31]

The neutral theory of molecular evolution, for example, is used to study evolution as a null model against which tests for natural selection can be applied. Phylogenetic theory is another example of evolutionary theory. It is based on the evolutionary premise of an ancestral descendant sequence of genes, populations, or species. Individuals that evolve are linked together through historical and genealogical ties. Evolutionary trees are hypotheses that are inferred through the practice of phylogenetic theory. They depict relations among individuals that can speciate and diverge from one another. The evolutionary process of speciation creates groups that are linked by a common ancestor and all its descendants. Species inherit traits, which are then passed on to descendants. Evolutionary biologists use systematic methods and test phylogenetic theory to observe and explain changes in and among species over time. These methods include the collection, measurement, observation, and mapping of traits onto evolutionary trees. Phylogenetic theory is used to test the independent distributions of traits and their various forms to provide explanations of observed patterns in relation to their evolutionary history and biology.[14][30]

Evolution compared with gravity

The application of the terms “fact” and “theory” to evolution is comparable to their use in describing gravity.[18] The most obvious fact of gravity is that objects in our everyday experience always fall downwards when not otherwise prevented from doing so. People throughout history have wondered what causes this effect. Many explanations have been proposed over the centuries. Aristotle, Galileo, Newton, and Einstein developed models of gravity, each of which constitutes a theory of gravity. Newton, for example, realized that the fact of gravity can be extended to the tendency of any two masses to attract one another. The word “gravity”, therefore, can be used to refer to the observed facts (i.e., that masses attract one another) and the theory used to explain the facts (the reason why masses attract one another). In this way, gravity is both a theory and a fact.

Evolution as theory and fact in the literature

The confusion over the word evolution and the distinction between “fact” and “theory” is largely due to authors using evolution to refer to three related yet distinct ideas: first, the changes that occur within species over generations; second, the mechanism thought to drive change; and third, the concept of common descent. However, among biologists there is a consensus that evolution is a fact:


  • American zoologist and paleontologist George Simpson stated that “Darwin… finally and definitely established evolution as a fact.”[32]
  • H. J. Muller wrote, “So enormous, ramifying, and consistant has the evidence for evolution become that if anyone could now disprove it, I should have my conception of the orderliness of the universe so shaken as to lead me to doubt even my own existence. If you like, then, I will grant you that in an absolute sense evolution is not a fact, or rather, that it is no more a fact than that you are hearing or reading these words.”[24]
  • Kenneth R. Miller writes, “evolution is as much a fact as anything we know in science.”[33]
  • Ernst Mayr observed, “The basic theory of evolution has been confirmed so completely that most modern biologists consider evolution simply a fact. How else except by the word evolution can we designate the sequence of faunas and floras in precisely dated geological strata? And evolutionary change is also simply a fact owing to the changes in the content of gene pools from generation to generation.”[34]


Evolution as fact and theory

Commonly “fact” is used to refer to the observable changes in organisms’ traits over generations while the word “theory” is reserved for the mechanisms that cause these changes:


  • Paleontologist Stephen Jay Gould writes, “Evolution is a theory. It is also a fact. And facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world’s data. Theories are structures of ideas that explain and interpret facts. Facts do not go away when scientists debate rival theories to explain them. Einstein’s theory of gravitation replaced Newton’s, but apples did not suspend themselves in mid-air, pending the outcome. And humans evolved from ape-like ancestors whether they did so by Darwin’s proposed mechanism or by some other yet to be discovered.”[1]
  • Similarly, biologist Richard Lenski says, “Scientific understanding requires both facts and theories that can explain those facts in a coherent manner. Evolution, in this context, is both a fact and a theory. It is an incontrovertible fact that organisms have changed, or evolved, during the history of life on Earth. And biologists have identified and investigated mechanisms that can explain the major patterns of change.”[35]
  • Biologist T. Ryan Gregory says, “biologists rarely make reference to ‘the theory of evolution,’ referring instead simply to ‘evolution’ (i.e., the fact of descent with modification) or ‘evolutionary theory’ (i.e., the increasingly sophisticated body of explanations for the fact of evolution). That evolution is a theory in the proper scientific sense means that there is both a fact of evolution to be explained and a well-supported mechanistic framework to account for it.”[18]


Evolution as fact not theory

Other commentators, focusing on the changes in species over generations and in some cases common ancestry have stressed that evolution is a fact to emphasize the weight of supporting evidence while denying it is helpful to use the term “theory”:


  • R. C. Lewontin wrote, “It is time for students of the evolutionary process, especially those who have been misquoted and used by the creationists, to state clearly that evolution is a fact, not theory.”[36]
  • Douglas Futuyma writes in his Evolutionary Biology book, “The statement that organisms have descended with modifications from common ancestors—the historical reality of evolution—is not a theory. It is a fact, as fully as the fact of the earth’s revolution about the sun.”[16]
  • Richard Dawkins says, “One thing all real scientists agree upon is the fact of evolution itself. It is a fact that we are cousins of gorillas, kangaroos, starfish, and bacteria. Evolution is as much a fact as the heat of the sun. It is not a theory, and for pity’s sake, let’s stop confusing the philosophically naive by calling it so. Evolution is a fact.”[37]
  • Neil Campbell wrote in his 1990 biology textbook, “Today, nearly all biologists acknowledge that evolution is a fact. The term theory is no longer appropriate except when referring to the various models that attempt to explain how life evolves… it is important to understand that the current questions about how life evolves in no way implies any disagreement over the fact of evolution.”[38]
  • Evolutionary scientist Kirk Fitzhugh[39] wrote, “‘Evolution’ cannot be both a theory and a fact. Theories are concepts stating cause–effect relations…One might argue that it is conceivable to speak of ‘evolution’ as a fact by way of it being the subject of reference in explanatory hypotheses…In the strictest sense then, ‘evolution’ cannot be regarded as a fact even in the context of hypotheses since the causal points of reference continue to be organisms, and no amount of confirming instances for those hypotheses will transform them into facts…While evolution is not a fact, it is also not a single theory, but a set of theories applied to a variety of causal questions… An emphasis on associating ‘evolution’ with ‘fact’ presents the misguided connotation that science seeks certainty.”[3]


Predictive Power

A central tenet in science is that a scientific theory is supposed to have predictive power, and verification of predictions are seen as an important and necessary support for the theory. The theory of evolution has provided such predictions[40] . Four examples are:


  • Genetic information must be transmitted in a molecular way that will be almost exact but permit slight changes. Since this prediction was made, biologists have discovered the existence of DNA, which has a mutation rate of roughly 10−9 per nucleotide per cell division; this provides just such a mechanism.[41]
  • Some DNA sequences are shared by very different organisms. It has been predicted by the theory of evolution that the differences in such DNA sequences between two organisms should roughly resemble both the biological difference between them according to their anatomy and the time that had passed since these two organisms have separated in the course of evolution, as seen in fossil evidence. The rate of accumulating such changes should be low for some sequences, namely those that code for critical RNA or proteins, and high for others that code for less critical RNA or proteins; but for every specific sequence, the rate of change should be roughly constant over time. These results have been experimentally confirmed. Two examples are DNA sequences coding for rRNA, which is highly conserved, and DNA sequences coding for fibrinopeptides (amino acid chains that are discarded during the formation of fibrin), which are highly non-conserved.[41]
  • Prior to 2004, paleontologists had found fossils of amphibians with necks, ears, and four legs, in rock no older than 365 million years old. In rocks more than 385 million years old they could only find fish, without these amphibian characteristics. Evolutionary theory predicted that since amphibians evolved from fish, an intermediate form should be found in rock dated between 365 and 385 million years ago. Such an intermediate form should have many fish-like characteristics, conserved from 385 million years ago or more, but also have many amphibian characteristics as well. In 2004, an expedition to islands in the Canadian arctic searching specifically for this fossil form in rocks that were 375 million years old discovered fossils of Tiktaalik.[42]
  • Evolutionary theory predicts that novel inventions can arise, while creationists predict that new “information” cannot arise, and that the Second Law of Thermodynamics only allows for “information” to be lost.[43] In an ongoing experiment, Richard Lenski observed that some strains of E. coli evolved the ability to metabolize citrate after tens of thousands of generations.[44]


Related concepts and terminology

To explain means to identify a mechanism that causes evolution, and to demonstrate the consequences of its operation. These consedquences are then the general laws of evolution, of which any given system or organism is a particular outcome.[45]:1


  • “Proof” of a theory has different meanings in science. Proof exists in formal sciences, such as a mathematical proof where symbolic expressions can represent infinite sets and scientific laws having precise definitions and outcomes of the terms. Proof has other meanings as it descends from its Latin roots (provable, probable, probare L.) meaning to test.[46][47] In this sense a proof is an inference to the best or most parsimonious explanation through a publicly verifiable demonstration (a test) of the factual (i.e., observed) and causal evidence from carefully controlled experiments. Charles Darwin’s research, for example, pointed to the coordination of so many pieces of evidence that no other configuration other than his theory could offer a conceivable causal explanation of the facts. In this way natural selection and common ancestry has been proven.[48] “The classical proof is the improvement of crops and livestock through artificial selection.”[45]:492 Natural selection and other evolutionary theories are also represented in various mathematical proofs, such as the Price equation. To remain consistent with the philosophy of science, however, advancement of theory is only achieved through disproofs of hypotheses.[49]
  • “Models” are part of the scientific or inferential “tool-kit” that are constructed out of preexistent theory. Model-based science uses idealized structures or mathematical expressions to strategically create simpler representations of complex worldly systems. Models are designed to resemble the relevant aspects of hypothetical relations in the target systems under investigation.[50][51]
  • Validation is a demonstration that a model within its domain of applicability possesses a satisfactory range of accuracy consistent with the intended application of the model.”[52]:233 Models are used in simulation research. For example, evolutionary phylogeneticists run simulations to model the tree like branching process of lineages over time. In turn, this is used to understand the theory of phylogenetics and the methods used to test for relations among genes, species, or other evolutionary units.[53]
  • A scientific law is a generalized formulation of the recurring observable tendencies of nature. Laws are based observations of events or processes that occur regularly and repeatedly under a defined set of conditions. Evolutionary laws are the demonstrated consequences of theoretical mechanisms, such as natural selection, neutral theory, niche construction, or other scientific theories. Branches in the diversity of life are the particular outcomes of the laws of evolution.[54][45]



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44.    ^ NS:bacteria make major evolutionary shift in the lab

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Charles Darwin in 1868

Darwinism is a set of movements and concepts related to ideas of transmutation of species or of evolution, including some ideas with no connection to the work of Charles Darwin.[1][2][3] The meaning of “Darwinism” has changed over time, and varies depending on who is using the term.[4] In the United States, the term “Darwinism” is often used by creationists as a pejorative term in reference to beliefs such as atheistic naturalism, but in the United Kingdom the term has no negative connotations, being freely used as a short hand for the body of theory dealing with evolution, and in particular, evolution by natural selection.[5]

The term was coined by Thomas Henry Huxley in April 1860,[6] and was used to describe evolutionary concepts, including earlier concepts such as Malthusianism and Spencerism. In the late 19th century it came to mean the concept that natural selection was the sole mechanism of evolution, in contrast to Lamarckism.[4] Around 1900 Darwinism was eclipsed by Mendelism until the modern evolutionary synthesis unified Darwin’s and Gregor Mendel‘s ideas. As modern evolutionary theory has developed, the term has been associated at times with specific ideas.[4]

While the term has remained in use amongst scientific authors, it has increasingly been argued that it is an inappropriate term for modern evolutionary theory.[7][8][9] For example, Darwin was unfamiliar with the work of Gregor Mendel,[10] and as a result had only a vague and inaccurate understanding of heredity. He naturally had no inkling of yet more recent developments and, like Mendel himself, knew nothing of genetic drift for example.[11]

Conceptions of Darwinism

As “Darwinism” became widely accepted in the 1870s, caricatures of Charles Darwin with an ape or monkey body symbolised evolution.[12]

While the term Darwinism had been used previously to refer to the work of Erasmus Darwin in the late 18th century, the term as understood today was introduced when Charles Darwin‘s 1859 book On the Origin of Species was reviewed by Thomas Henry Huxley in the April 1860 issue of the Westminster Review.[13] Having hailed the book as, “a veritable Whitworth gun in the armoury of liberalism” promoting scientific naturalism over theology, and praising the usefulness of Darwin’s ideas while expressing professional reservations about Darwin’s gradualism and doubting if it could be proved that natural selection could form new species,[14] Huxley compared Darwin’s achievement to that of Copernicus in explaining planetary motion:

What if the orbit of Darwinism should be a little too circular? What if species should offer residual phenomena, here and there, not explicable by natural selection? Twenty years hence naturalists may be in a position to say whether this is, or is not, the case; but in either event they will owe the author of “The Origin of Species” an immense debt of gratitude…… And viewed as a whole, we do not believe that, since the publication of Von Baer’s “Researches on Development,” thirty years ago, any work has appeared calculated to exert so large an influence, not only on the future of Biology, but in extending the domination of Science over regions of thought into which she has, as yet, hardly penetrated.[6]

Another important evolutionary theorist of the same period was Peter Kropotkin who, in his book Mutual Aid: A Factor of Evolution, advocated a conception of Darwinism counter to that of Huxley. His conception was centred around what he saw as the widespread use of co-operation as a survival mechanism in human societies and animals. He used biological and sociological arguments in an attempt to show that the main factor in facilitating evolution is cooperation between individuals in free-associated societies and groups. This was in order to counteract the conception of fierce competition as the core of evolution, which provided a rationalisation for the dominant political, economic and social theories of the time; and the prevalent interpretations of Darwinism, such as those by Huxley, who is targeted as an opponent by Kropotkin. Kropotkin’s conception of Darwinism could be summed up by the following quote:

In the animal world we have seen that the vast majority of species live in societies, and that they find in association the best arms for the struggle for life: understood, of course, in its wide Darwinian sense – not as a struggle for the sheer means of existence, but as a struggle against all natural conditions unfavourable to the species. The animal species, in which individual struggle has been reduced to its narrowest limits, and the practice of mutual aid has attained the greatest development, are invariably the most numerous, the most prosperous, and the most open to further progress. The mutual protection which is obtained in this case, the possibility of attaining old age and of accumulating experience, the higher intellectual development, and the further growth of sociable habits, secure the maintenance of the species, its extension, and its further progressive evolution. The unsociable species, on the contrary, are doomed to decay.

Peter Kropotkin, Mutual Aid: A Factor of Evolution (1902), Conclusion.

19th-Century Usage

“Darwinism” soon came to stand for an entire range of evolutionary (and often revolutionary) philosophies about both biology and society. One of the more prominent approaches, summed in the 1864 phrase “survival of the fittest” by the philosopher Herbert Spencer, later became emblematic of Darwinism even though Spencer’s own understanding of evolution (as expressed in 1857) was more similar to that of Jean-Baptiste Lamarck than to that of Darwin, and predated the publication of Darwin’s theory in 1859. What is now called “Social Darwinism” was, in its day, synonymous with “Darwinism” — the application of Darwinian principles of “struggle” to society, usually in support of anti-philanthropic political agenda. Another interpretation, one notably favoured by Darwin’s half-cousin Francis Galton, was that “Darwinism” implied that because natural selection was apparently no longer working on “civilized” people, it was possible for “inferior” strains of people (who would normally be filtered out of the gene pool) to overwhelm the “superior” strains, and voluntary corrective measures would be desirable — the foundation of eugenics.

In Darwin’s day there was no rigid definition of the term “Darwinism,” and it was used by opponents and proponents of Darwin’s biological theory alike to mean whatever they wanted it to in a larger context. The ideas had international influence, and Ernst Haeckel developed what was known as Darwinismus in Germany, although, like Spencer’s “evolution”, Haeckel’s “Darwinism” had only a rough resemblance to the theory of Charles Darwin, and was not centred on natural selection at all. In 1886 Alfred Russel Wallace went on a lecture tour across the United States, starting in New York and going via Boston, Washington, Kansas, Iowa and Nebraska to California, lecturing on what he called “Darwinism” without any problems.[15]

Other Uses

The term Darwinism is often used in the United States by promoters of creationism, notably by leading members of the intelligent design movement, as an epithet to attack evolution as though it were an ideology (an “ism”) of philosophical naturalism, or atheism.[16] For example, Phillip E. Johnson makes this accusation of atheism with reference to Charles Hodge‘s book What Is Darwinism?.[17] However, unlike Johnson, Hodge confined the term to exclude those like Asa Gray who combined Christian faith with support for Darwin’s natural selection theory, before answering the question posed in the book’s title by concluding: “It is Atheism.”[18][19][20] Creationists use the term Darwinism, often pejoratively, to imply that the theory has been held as true only by Darwin and a core group of his followers, whom they cast as dogmatic and inflexible in their belief.[21] In the 2008 movie Expelled: No Intelligence Allowed which promotes intelligent design, Ben Stein persistently refers to “scientists” as Darwinists. Reviewing the film for Scientific American, John Rennie says “The term is a curious throwback, because in modern biology almost no one relies solely on Darwin’s original ideas… Yet the choice of terminology isn’t random: Ben Stein wants you to stop thinking of evolution as an actual science supported by verifiable facts and logical arguments and to start thinking of it as a dogmatic, atheistic ideology akin to Marxism.” [22]

However, Darwinism is also used neutrally within the scientific community to distinguish modern evolutionary theories, sometimes called “NeoDarwinism”, from those first proposed by Darwin. Darwinism also is used neutrally by historians to differentiate his theory from other evolutionary theories current around the same period. For example, Darwinism may be used to refer to Darwin’s proposed mechanism of natural selection, in comparison to more recent mechanisms such as genetic drift and gene flow. It may also refer specifically to the role of Charles Darwin as opposed to others in the history of evolutionary thought — particularly contrasting Darwin’s results with those of earlier theories such as Lamarckism or later ones such as the modern synthesis.

In the United Kingdom the term retains its positive sense as a reference to natural selection, and for example Richard Dawkins wrote in his collection of essays A Devil’s Chaplain, published in 2003, that as a scientist he is a Darwinist.[23]


1.       ^ John Wilkins (1998). “How to be Anti-Darwinian”. TalkOrigins Archive. Retrieved 19 June 2008.

2.       ^ “Expelled Exposed: Why Expelled Flunks » …on what evolution explains”. National Center for Science Education. Retrieved 22 December 2008.

3.       ^ based on a European Southern Observatory release (9 December 2006). “Galactic Darwinism :: Astrobiology Magazine – earth science – evolution distribution Origin of life universe – life beyond :: Astrobiology is study of earth science evolution distribution Origin of life in universe terrestrial”. Retrieved 22 December 2008.

4.       ^ a b c Joel Hanes. “What is Darwinism?”. TalkOrigins Archive. Retrieved 19 June 2008.

5.       ^ Scott, Eugenie C.; Branch, Glenn (16 January 2009). “Don’t Call it “Darwinism””. Evolution: Education and Outreach (New York: Springer) 2 (1): 90. doi:10.1007/s12052-008-0111-2. ISSN 1936-6434. Retrieved 17 November 2009.

6.       ^ a b Huxley, T.H. (April 1860). “ART. VIII.- Darwin on the origin of Species”. Westminster Review. pp. 541–70. Retrieved 19 June 2008. “What if the orbit of Darwinism should be a little too circular?”

7.       ^ John Wilkins (1998). “How to be Anti-Darwinian”. TalkOrigins Archive. Retrieved 27 June 2008.

8.       ^ Ruse, Michael (2003). Darwin and Design: Does Evolution Have a Purpose?. Cambridge, MA: Harvard University Press. pp. 293. ISBN 0674016319. Retrieved 18 July 2008.

9.       ^ Olivia Judson (15 July 2008). “Let’s Get Rid of Darwinism”. New York Times.

10.   ^ Sclater, Andrew (June 2006). “The extent of Charles Darwin’s knowledge of Mendel”. Journal of Biosciences (Bangalore, India: Springer India / Indian Academy of Sciences) 31 (2): 191–193. doi:10.1007/BF02703910. PMID 16809850. Retrieved 3 January 2009.

11.   ^ Laurence Moran (1993). “Random Genetic Drift”. TalkOrigins Archive. Retrieved 27 June 2008.

12.   ^ Browne 2002, pp. 376–379

13.   ^ “The Huxley File § 4 Darwin’s Bulldog”. Retrieved 29 June 2008.

14.   ^ Browne 2002, pp. 105–106

15.   ^ “Evolution and Wonder – Understanding Charles Darwin – Speaking of Faith from American Public Media”. Retrieved 27 July 2007.

16.   ^ Scott, Eugenie C. (2008). “Creation Science Lite: “Intelligent Design” as the New Anti-Evolutionism”. In Godfrey, Laurie R.; Petto, Andrew J.. Scientists Confront Creationism: Intelligent Design and Beyond. New York: W. W. Norton. pp. 72. ISBN 0-393-33073-7.

17.   ^ Johnson, Phillip E.. “What is Darwinism?”. Retrieved 4 January 2007.

18.   ^ Matthew, Ropp. “Charles Hodge and His Objection to Darwinism”. Retrieved 4 January 2007.

19.   ^ Hodge, Charles. “What is Darwinism?”. Retrieved 4 January 2007.

20.   ^ Hodge, Charles (1874). What is Darwinism?. Scribner, Armstrong, and Company. OCLC 11489956.

21.   ^ Sullivan, M (2005). “From the Beagle to the School Board: God Goes Back to School”. Impact Press. Retrieved 18 September 2008.

22.   ^ Ben Stein’s Expelled: No Integrity Displayed, Scientific American.

23.   ^ Sheahen, Laura. Religion: For Dummies., interview about 2003 book.