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| {{otheruses4|the history of evolutionary thought in biology|the history of evolutionary thought in the social sciences|Social evolutionism|the history of religious discussions|Creation-evolution controversy}} | |||
| ] in ''The Evolution of Man'' (1879) illustrates the 19th-century view that evolution was a progressive process leading towards man.]] | |||
| '''Evolutionary thought''', the concept that species change over time, has roots in ], in the ideas of the ], ], ] and ]. However, until the 18th century, ] biological thinking was dominated by ], the belief that every species has essential characteristics that are unalterable. This began to change when, during the ], evolutionary ] and the ] spread from the ] to ]. ] began to focus on the variability of species; the emergence of ] with the concept of ] further undermined the static view of nature. In the early 19th century, ] proposed his theory of the ], the first fully formed scientific theory of ]. | |||
| In 1858, ] and ] published a new evolutionary theory, which was explained in detail in Darwin's '']'' (1859). Unlike Lamarck, Darwin proposed ] and a branching ]. The theory was based on the idea of ], and it synthesized a broad range of evidence from ], ], ], ], and ]. | |||
| Darwin's work led to the rapid acceptance of the general concept of evolution, but the specific mechanism he proposed, ], was not widely accepted until the 1940s. Most biologists argued that other factors were responsible for ], such as ] (neo-Lamarckism), an innate drive for change (]), or sudden large mutations (]). The synthesis of natural selection with ] during the 1920s and 1930s founded the new discipline of ]. 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 ]. | |||
| Following the establishment of ], studies of ] and ] in natural populations, combined with ] and ], led to sophisticated mathematical and causal models of evolution. Paleontology and ] allowed more detailed reconstructions of the ]. After the rise of ] in the 1950s, the field of ] developed, based on ] and ] tests, and later incorporating ] and ] studies. The ] rose to prominence in the 1960s, followed by the ], sparking debates over ], the ], and the relative importance of ] versus natural selection. In the late 20th century, ] led to ] and the reorganization of the tree of life into the ]. In addition, the newly recognized factors of ] and ] introduced yet more complexity into evolutionary history. | |||
| <br style="clear:right;"/>{{evolution3}} | |||
| ==Antiquity== | |||
| ===Greeks=== | |||
| ] discussed ideas that involved forms of organic evolution. ] (c. 610–546 BC) proposed that life had originally developed in the sea and only later moved onto land, and ] (c. 490–430 BC) wrote of a non-supernatural origin for living things.<ref>{{cite web|last=Campbell|first=Gordon|title=Empedocles|publisher=Internet Encyclopedia of Philosophy|url=http://www.iep.utm.edu/e/empedocl.htm#H4|accessdate=2008-07-15}}</ref> Empedocles suggested that ] did not require an organizer or ]. Aristotle summarized his idea as: "Wherever then all the parts came about just what they would have been if they had come be for an end, such things survived, being organized spontaneously in a fitting way; whereas those which grew otherwise perished and continue to perish..." <ref>{{cite web|last=Hardie|first=R.P.|coauthors=R. K. Gaye|title=Physics by Aristotle|url=http://classics.mit.edu/Aristotle/physics.2.ii.html|accessdate=2008-07-15}}</ref> | |||
| ] (c. 428–348 BC) was, in the words of biologist and historian ], "the great antihero of evolutionism",<ref> {{wikiref |id=Mayr-1982|text= Mayr 1982 p. 304}}</ref> as he established the philosophy of ], which he called the ]. This theory holds that objects observed in the real world are only ''reflections'' of a limited number of ]s (''eide''). Variation is merely the result of an imperfect reflection of these constant essences. In his '']'', Plato set forth the idea that the ] had created the ] 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 idea, that all potential forms of life are essential to a perfect creation, is called the ], and it greatly influenced Christian thought.<ref name=oet>{{cite web | last = Johnston | first = Ian | title =Section Three: The Origins of Evolutionary Theory | work =. . . And Still We Evolve: A Handbook on the History of Modern Science | publisher =Liberal Studies Department, Malaspina University College | year =1999 | url =http://www.mala.bc.ca/~johnstoi/darwin/sect3.htm | accessdate =2007-08-11 }}</ref> | |||
| ] (384–322 BC), one of the most influential of the Greek philosophers, is the earliest natural historian whose work has been preserved in any real detail. His writings on biology were the result of his research into natural history on and around the isle of ], and have survived in the form of four books, usually known by their ] names, '']'' (on the essence of life), '']'' (inquiries about animals), '']'' (reproduction), and '']'' (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.<ref name="Singer_SHB"> {{wikiref |id=Singer-1931|text=Singer 1931}}</ref> However, for ], "Nothing is more remarkable than efforts to the relationships of living things as a ''scala naturæ''".<ref name="Singer_SHB"/> This '']'', described in ''Historia animalium'', classified organisms in relation to a hierarchical "Ladder of Life" or "Chain of Being", placing them according to complexity of structure and function, with organisms that showed greater vitality and ability to move described as "higher organisms".<ref name=oet/> | |||
| ===Chinese=== | |||
| Ideas on evolution were expressed by ancient ] such as ] (Chuang Tzu), a Taoist philosopher who lived around the 4th century BC. According to ], ] explicitly denied the fixity of biological species and Taoist philosophers speculated that species had developed differing attributes in response to differing environments.<ref>{{wikiref|id=Needham-1995|text= Needham and Ronan 1995 p. 101}}</ref> Humans, nature and the heavens were seen as existing in a state of "constant transformation" known as the ] in contrast with the more static view of nature typical of Western thought.<ref>{{Cite web |author = Miller, James |title = Daoism and Nature |publisher = Royal Asiatic Society |date=January 8, 2008 |url = http://www.jamesmiller.ca/RAS%20lecture%20on%20daoism%20and%20nature.pdf|format=PDF|accessdate=2008-07-15}}</ref> | |||
| ===Romans=== | |||
| Titus ] Carus (d. 50 BC), the Roman philosopher and ], wrote the poem '']'' (''De rerum natura''), which provides the best surviving explanation of the ideas of the Greek ] 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 ].<ref>{{Cite web |author = Sedley, David |title = Lucretius |publisher = Stanford Encyclopedia of Philosophy|date=August 4, 2004 |url = http://plato.stanford.edu/entries/lucretius/|accessdate=2008-07-24}}</ref><ref>{{Cite web |author = Simpson, David |title = Lucretius |publisher = The Internet Encyclopedia of Philosophy|year=2006 |url = http://www.iep.utm.edu/l/lucretiu.htm|accessdate=2008-07-24}}</ref> | |||
| ==Middle Ages== | |||
| ===Islamic philosophy and the struggle for existence=== | |||
| {{main|Early Islamic philosophy#Evolution|l1=Early Islamic philosophy – Evolution}} | |||
| Whereas Greek and Roman evolutionary ideas died out in Europe after the fall of the ], they were not lost to ] and ]. In the ], early theories on evolution were taught in ].<ref name="Draper" /> ], the 19th-century scientist, philosopher and historian, discussed the 12th-century writings of ] as part of what he called the "] theory of evolution". He compared these early ideas to later biological theories, arguing that the former were developed "... much farther than we are disposed to do, extending them even to inorganic or mineral things."<ref name="Draper">{{wikiref|id=Draper-1878|text=Draper 1878 pp. 154–155, 237}}</ref> | |||
| The first ] and philosopher to speculate in detail about evolution was the ] writer ] in the 9th century. He considered the effects of the environment on an animal's chances for survival, and described the struggle for existence.<ref>Conway Zirkle (1941). Natural Selection before the "Origin of Species", ''Proceedings of the American Philosophical Society'' '''84''' (1), pp. 71–123.</ref><ref name="IslamicQuarterly">Mehmet Bayrakdar (Third Quarter, 1983). "Al-Jahiz And the Rise of Biological Evolutionism", ''The Islamic Quarterly''. ]. </ref> ]'s ''al-Fawz al-Asghar'' and the ]'s '']'' (''The Epistles of Ikhwan al-Safa'') expressed ideas about how species developed: from matter into vapor and thence to water, then minerals into plants and then animals, leading to apes and, finally, humans.<ref>] and Afzal Iqbal (1993), ''The Emergence of Islam: Lectures on the Development of Islamic World-view, Intellectual Tradition and Polity'', pp. 143–144. Islamic Research Institute, Islamabad.</ref><ref name=Hart>Eloise Hart, ''Pages of Medieval Mideastern History''. (] Isma'ili, Yezidi, Sufi, , Ismaili Heritage Society)</ref> The ] ] wrote a book in which he argued for ] (although not natural selection). Numerous other Islamic scholars and scientists, such as ], ], and ] discussed and developed these ideas. ], these works began to appear in the West after the ] and may have had an impact on Western science.<ref name="IslamicQuarterly"/> | |||
| ===Christian philosophy and the great chain of being=== | |||
| ] from ''Retorica Christiana'' (1579) by Didacus Valdes]] | |||
| During the ], Greek classical learning was all but lost to the West. However, contact with the ], where Greek manuscripts were preserved and elaborated on, soon led to a massive spate of ]. Europeans were thus re-introduced to the works of Plato and Aristotle, as well as to ]. ] of the ] school, in particular ] and ], 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 ].<ref> {{wikiref |id=Lovejoy-1936|text= Lovejoy 1936 p. 67–80}}</ref><ref name=oet/> | |||
| Within this system, everything that existed could be placed in order, from "lowest" to "highest", with ] 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 must remain forever fixed, in accordance with the text of '']''. 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.<ref name=oet/> | |||
| Creatures on adjacent steps were expected to closely resemble each other, an idea expressed in the saying: {{lang|la|''natura non facit saltum''}} ("nature does not make leaps").<ref name=oet/> This basic concept of the great chain of being greatly influenced the thinking of ] for centuries (and still has an influence today). It also formed a part of the ] presented by ]. As a classification system, it became the major organizing principle and foundation of the emerging science of ] in the 17th and 18th centuries.<ref name=oet/> | |||
| ==Renaissance and Enlightenment== | |||
| {{Main article|Evolutionary ideas of the renaissance and enlightenment}} | |||
| ] compared the skeletons of birds and humans in his ''Book of Birds'' (1555).]] | |||
| Some ] theories explored between 1650 and 1800 postulated that the universe, including life on Earth, had developed mechanically, entirely without divine guidance. Around this time, the ] of ] began to encourage the machine-like view of the universe which would come to characterise the ].<ref> {{wikiref|id=Bowler-2003|text=Bowler 2003 pp. 33–38}} </ref> However, most contemporary theories of evolution, such of those of ] and ], held that evolution was a fundamentally ''spiritual'' process.<ref>Schelling, ''System of Transcendental Idealism'', 1800</ref> In 1751, ] veered toward more ] ground. He wrote of natural modifications occurring during reproduction and accumulating over the course of many generations, producing races and even new species, and he anticipated in general terms the idea of natural selection.<ref> {{wikiref|id=Bowler-2003|text= Bowler 2003 pp. 73–75}}</ref> | |||
| Later in the 18th century, the French natural philosopher ] 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 speculated that the 200 or so species of mammals then known might have descended from as few as 38 original forms. Buffon’s evolutionary ideas were limited; he believed each of the original forms had arisen through spontaneous generation and that they were shaped by "internal moulds" that limited the amount of change. Buffon was one of the leading 18th century naturalists and his works ''Natural History'', and ''The Epochs of Nature'' that contained well developed theories about a completely materialistic origin for the Earth, as well as his ideas questioning the fixity of species, were extremely influential.<ref>{{wikiref|id=Bowler-2003|text= Bowler 2003 pp. 75–80}}</ref><ref>{{wikiref|id=Larson-2004|text= Larson 2004 pp. 14–15}}</ref> | |||
| Between 1767 and 1792, ] 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.<ref>{{wikiref|id=Henderson-2000| text=Henderson 2000}}</ref> Charles Darwin’s grandfather, ], published '']'' in 1796, which suggested that "all warm-blooded animals have arisen from one living filament".<ref> {{wikiref|id=Darwin-1818|text=Darwin, Erasmus 1818 Vol I section XXXIX}}</ref> In his 1802 poem ''Temple of Nature'', he described the rise of life from minute organisms living in the mud to all of its modern diversity.<ref>{{wikiref|id=Darwin-1825|text= Darwin, Erasmus 1825 p. 15}}</ref><br /></blockquote> | |||
| ==Early 19th century== | |||
| ] showing the appearance of major animal types]] | |||
| ===Paleontology and geology=== | |||
| {{seealso|History of paleontology}} | |||
| In 1796, ] published his findings on the differences between living ]s and those found in the ] record. His analysis demonstrated that ]s and ]s were distinct species different from any living animal, effectively ending a long-running debate over the possibility of the extinction of a species.<ref>{{wikiref|id=Larson-2004|text = Larson 2004 p. 7}} </ref> In 1788, ] described ] geological processes operating continuously over ].<ref name=JH>{{cite web |url= http://www.amnh.org/education/resources/rfl/web/essaybooks/earth/p_hutton.html |title= James Hutton: The Founder of Modern Geology |author= ] |work= Earth: Inside and Out |year= 2000 |quote=we find no vestige of a beginning, no prospect of an end. }}</ref> ] began the process of ordering ] by examining fossils in the layers while he worked on his geologic map of ]. Independently, in 1811, Georges Cuvier and ] published an influential study of the geologic history of the region around Paris, based on the ] succession of rock layers. These works helped establish the antiquity of the Earth.<ref> {{wikiref|id=Bowler-2003|text=Bowler 2003 p. 113}} </ref> Cuvier advocated ] to explain the patterns of extinction and ] 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 ] were becoming clear, and in 1841 ] named three major eras, based on the predominant fauna of each: the ], dominated by marine ]s and fish, the ], the age of reptiles, and the current ] age of mammals. This progressive picture of the history of life was accepted even by conservative English geologists like ] and ]; however, like Cuvier, they attributed the progression to repeated catastrophic episodes of extinction followed by new episodes of creation.<ref> {{wikiref|id=Larson-2004|text = Larson 2004 pp. 29–38}} </ref> Unlike Cuvier, Buckland and some other advocates of ] among British geologists made efforts to explicitly link the last catastrophic episode proposed by Cuvier to the ].<ref> {{wikiref|id=Bowler-2003|text=Bowler 2003 pp. 115–116}} </ref><ref name=Darwindesign>{{cite web|url=http://www.darwinproject.ac.uk/content/view/110/104/|title=Darwin and design: historical essay|publisher=Darwin Correspondence Project|accessdate=2008-01-17}}</ref> | |||
| From 1830 to 1833, ] published his multi-volume work '']'', which, building on Hutton's ideas, advocated a ] 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 ].<ref name="Bowler129-134"> {{wikiref|id=Bowler-2003|text=Bowler 2003 pp. 129–134}} </ref> | |||
| ===Transmutation of species=== | |||
| {{main article|Transmutation of species}} | |||
| ] | |||
| ] proposed, in his '']'' 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 ]. 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 ] that would become known as ] and would influence discussions of evolution into the 20th century.<ref> {{wikiref|id=Bowler-2003|text= Bowler 2003 pp. 86–94}} </ref><ref> {{wikiref|id=Larson-2004|text= Larson 2004 pp. 38–41}} </ref> | |||
| A radical British school of comparative anatomy that included the ] ] was closely in touch with Lamarck's French school of ''Transformationism''. One of the French scientists who influenced Grant was the anatomist ], whose ideas on the unity of various animal body plans and the ] of certain anatomical structures would be widely influential and lead to intense debate with his colleague ]. Grant became an authority on the anatomy and reproduction of marine ]. He developed Lamarck's and ]'s ideas of ] and ], and investigated homology to prove ]. 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 ], 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.<ref> {{wikiref|id=Desmon-1994|text=Desmond and Moore 1993 p. 40}} </ref><ref name="Bowler120-129"> {{wikiref|id=Bowler-2003|text= Bowler 2003 pp. 120–129}} </ref> | |||
| In 1844, the Scottish publisher ] anonymously published an extremely controversial but widely-read book entitled '']''. 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.<ref> {{wikiref|id=Bowler-2003|text = Bowler 2003 pp. 134–138}} </ref><ref> {{wikiref|id=Bowler-2005|text=Bowler and Morus 2005 pp. 142–143}} </ref> | |||
| Ideas about the transmutation of species were associated with the radical materialism of the ] and were attacked by more conservative thinkers. ] 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.<ref> {{wikiref|id=Larson-2004|text= Larson 2004 pp. 5–24}} </ref> | |||
| ] | |||
| In Britain the philosophy of ] remained influential. ]'s 1802 book ''Natural Theology'' with its famous ] had been written at least in part as a response to the transmutational ideas of ].<ref> {{wikiref|id=Bowler-2003|text=Bowler 2003 pp. 103–104}} </ref> 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''.<ref> {{wikiref|id=Larson-2004|text= Larson 2004 pp. 37–38}} </ref><ref> {{wikiref|id=Bowler-2003|text=Bowler 2003 p. 138}} </ref> Although the geologist ] 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.<ref name="Bowler129-134"/> Idealists such as ] and ] 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 ], 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 ], such as ] 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'', would contribute to his decision to delay publishing his ideas.<ref name="Bowler120-129"/><ref>{{wikiref|id=Larson-2004|text= Larson 2004 pp. 42–46}}</ref> | |||
| ===Anticipations of natural selection=== | |||
| Several writers anticipated aspects of Darwin's theory, and in the third edition of '']'' 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.<ref>{{harvnb|Darwin|1861|p=}}</ref> | |||
| In 1813, ] read before the ] essays assuming that there had been evolution of humans, and recognising the principle of ]. 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."<ref>{{harvnb|Darwin|1866|p=}}</ref> When Darwin was developing his theory, he was influenced by ]'s ''natural system'' of classification, which laid emphasis on the war between competing species.<ref>{{wikiref|id=Bowler-2003|text=Bowler 2003 p. 151}}</ref><ref>{{harvnb|Darwin|1859|p=}}</ref> | |||
| ] wrote in the obscure book ''Naval Timber & Arboriculture'' (1831) of "continual balancing of life to circumstance. ... progeny of the same parents, under great differences of circumstance, might, in several generations, even become distinct species, incapable of co-reproduction."<ref>{{cite web|last=Matthew|first=Patrick|title=Nature's law of selection. Gardeners' Chronicle and Agricultural Gazette |url=http://darwin-online.org.uk/content/frameset?itemID=A143&viewtype=text&pageseq=1|publisher=The Complete Works of Charles Darwin Online|year=1860|accessdate=2007-11-01}}</ref> 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."<ref>{{harvnb|Darwin|1861|p=}}</ref> | |||
| 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 ] 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.<ref> {{wikiref|id=Bowler-2003|text=Bowler 2003 p. 158}} </ref> | |||
| ] said in his essay on the reception of the ''Origin of Species'': | |||
| <blockquote> | |||
| 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 ].<ref>{{cite web|last=Huxley|first=Thomas Henry|title=''The Reception of the Origin of Species'' |url=http://infomotions.com/etexts/gutenberg/dirs/etext00/oroos10.htm|publisher=Project Gutenberg|year=1895|accessdate=2007-11-02}}</ref> | |||
| </blockquote> | |||
| ] | |||
| ===Natural selection=== | |||
| {{main|Inception of Darwin's theory|Development of Darwin's theory|Publication of Darwin's theory}} | |||
| The ] patterns Charles Darwin observed in places such as the ] during ] caused him to doubt the fixity of species, and in 1837 Darwin started the first of a series of secret notebooks on ]. Darwin's observations lead 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 '']'', written in the late 1700s by ]. Malthus' idea of population growth leading to a struggle for survival combined with Darwin's knowledge on how breeders selected traits, led to the ] of ]. Darwin did not publish his ideas on evolution for 20 years. However he did share them with certain other naturalists and friends, starting with ], 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.<ref>{{wikiref|id=Bowler-2005|text=Bowler and Morus pp. 129–149}}</ref><ref>{{wikiref|id=Larson-2004|text=Larson 2004 pp. 55–71}}</ref><ref>{{cite web|last=van Wyhe|first=John|title=Mind the gap: Did Darwin avoid publishing his theory for many years?|url=http://darwin-online.org.uk/people/van_Wyhe_2007_Mind_the_gap_did_Darwin_avoid_publishing_his_theory.pdf|format=PDF|publisher=Notes and Records of the Royal Society|accessdate=2008-07-16}}</ref> | |||
| Unlike Darwin, ], influenced by the book '']'', 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 ] and the ] 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 ]. Darwin also began work in earnest on ''The Origin of Species'', which he would publish in 1859.<ref>{{wikiref|id=Bowler-2003|text=Bowler 2003 pp. 173–176}}</ref> | |||
| ] 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== | |||
| {{see also|Reaction to Darwin's theory}} | |||
| By the 1850s whether or not species evolved was a subject of intense debate, with prominent scientists arguing both sides of the issue.<ref>{{wikiref|id=Larson-2004|text=Larson 2004 p. 50}}</ref> However, it was the publication of Charles Darwin's '']'' (1859) that fundamentally transformed the discussion over biological origins.<ref>The centrality of ''Origin of Species'' in the rise of widespread evolutionary thinking has been has long been accepted by historians of science. However, some scholars have recently begun to challenge this idea. James A. Secord, in his study of the impact of ''Vestiges of the Natural History of Creation'', argues that in some ways ''Vestiges'' had as much or more impact than ''Origin'', at least into the 1880s. Focusing so much on Darwin and ''Origin'', he argues, "obliterates decades of labor by teachers, theologians, technicians, printers, editors, and other researchers, whose work has made evolutionary debates so significant during the past two centuries." {{wikiref|id=Secord-2000|text=Secord 2000 pp. 515–518}}</ref> 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.<ref name="Larson79-111">{{wikiref|id=Larson-2004|text=Larson 2004 pp. 79–111}}</ref> | |||
| One of the first and most important naturalists to be convinced by ''Origin'' of the reality of evolution was the British anatomist ]. 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 ] was the key evolutionary mechanism. Huxley would make advocacy of evolution a cornerstone of the program of the ] to reform and professionalise science by displacing ] with ] 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.<ref name="Larson79-111"/> 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 '']'' 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 ] from its small five-toed ancestors.<ref>{{wikiref|id=Larson-2004|text= Larson 2004 pp. 139–40}}</ref> 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 ] and ] 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.<ref>{{wikiref|id=Larson-2004|text= Larson 2004 pp. 109–110}}</ref> | |||
| Darwin's theory succeeded in profoundly altering scientific opinion regarding the development of life and in producing a small philosophical revolution.<ref>{{wikiref|id=Bowler-2003|text=Bowler 2003 pp. 177–223}}</ref> 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 ], while relying in part on the inheritance of ], proved to be useful for statistical models of evolution that were developed by his cousin ] and the "biometric" school of evolutionary thought. However, this idea proved to be of little use to other biologists.<ref>{{wikiref|id=Larson-2004|text= Larson 2004 pp. 121–123, 152-157}}</ref> | |||
| ===Application to humans=== | |||
| ]'s book '']'' (1863).]] | |||
| 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 ] 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 ]'s 1863 book '']'', 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 ] in the 1890s were either of anatomically modern humans, or of ]s 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.<ref name="Bowler207-216">{{wikiref|id=Bowler-2003|text=Bowler 2003 pp. 207–216}}</ref> | |||
| Therefore the debate that immediately followed the publication of ''The Origin of Species'' centered on the similarities and differences between humans and modern ]s. ] had been criticised in the 18th century for grouping humans and apes together as primates in his ground breaking classification system.<ref>{{wikiref|id=Bowler-2003|text=Bowler 2003 pp. 49–51}}</ref> ] vigorously defended the classification suggested by Cuvier and ] 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, ] sought to demonstrate a close anatomical relationship between humans and apes. In one famous incident, Huxley showed that Owen was mistaken in claiming that the brains of ]s lacked a structure present in human brains. Huxley summarized his argument in his highly influential 1863 book '']''. Another viewpoint was advocated by Charles Lyell and ]. 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.<ref name="Bowler207-216"/> | |||
| In 1871, Darwin published '']'', 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 ]. The debate over human origins, and over the degree of human uniqueness continued well into the 20th century.<ref name="Bowler207-216"/> | |||
| ===Alternatives to natural selection=== | |||
| {{main|The eclipse of Darwinism}} | |||
| ] horns over time, which Osborn claimed was an example of an orthogenic trend in evolution.]] | |||
| Evolution was widely accepted in scientific circles within a few years of the publication of ''Origin'', but the acceptance of ] as its driving mechanism was much less widespread. The four major alternatives to natural selection in the late 19th century were ], ], ], and ]. Theistic evolution (a term promoted by Darwin's greatest American advocate ]) 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 ] 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.<ref name="Larson105-129">{{wikiref|id=Larson-2004|text= Larson 2004 pp. 105–129}}</ref><ref name="Bowler196-250">{{wikiref|id=Bowler-2003|text= Bowler 2003 pp. 196–253}}</ref> | |||
| In the late 19th century, the term ] 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 ], the German biologist ], and the American paleontologist ]. 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 ] of evolution, which held that the embryological development of an organism repeats its evolutionary history.<ref name="Larson105-129"/><ref name="Bowler196-250"/> Critics of neo-Lamarckism, such as the German biologist ] and ], 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.<ref name="Larson105-129"/><ref name="Bowler196-250"/> | |||
| Orthogenesis was the ] 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 Berg and the American paleontologist ]. 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 ], ], and early in his career, ]. It became the basis of the ] of evolution.<ref name="Larson105-129"/><ref name="Bowler196-250"/> | |||
| ]'']] | |||
| ===Mendelian genetics, biometrics, and mutation=== | |||
| The so-called rediscovery of ]'s laws of inheritance in 1900 ignited a fierce debate between two camps of biologists. In one camp were the ]s, who were focused on discrete variations and the laws of inheritance. They were led by ] (who coined the word '']'') and ] (who coined the word '']''). Their opponents were the ], who were interested in the continuous variation of characteristics within populations. Their leaders, ] and ], followed in the tradition of ], who had focused on measurement and ] 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.<ref name="Bowler256-273">{{wikiref|id=Bowler-2003|text= Bowler 2003 pp. 256–273}}</ref><ref name="Larson153-174">{{wikiref|id=Larson-2004|text= Larson 2004 pp. 153–174}}</ref> | |||
| When ] began experimenting with breeding the fruit fly '']'', 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.<ref name="Bowler256-273"/><ref name="Larson153-174"/> | |||
| ==1920s–1940s== | |||
| {{seealso|Modern evolutionary synthesis}} | |||
| {{Double image stack|left|Biston.betularia.7200.jpg|Biston.betularia.f.carbonaria.7209.jpg|200|''Biston betularia f. typica'' is the white-bodied form of the ].|''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 ]. A key step was the work of the British biologist and statistician ]. In a series of papers starting in 1918 and culminating in his 1930 book '']'', Fisher showed that the continuous variation measured by the biometricians could be produced by the combined action of many discrete genes, and that ] could change ] in a population, resulting in evolution. In a series of papers beginning in 1924, another British geneticist, ], applied statistical analysis to real-world examples of natural selection, such as the ], and showed that natural selection worked at an even faster rate than Fisher assumed.<ref name="Bowler325-339">{{wikiref|id=Bowler-2003|text=Bowler 2003 pp. 325–339}}</ref><ref name="Larson221-243">{{wikiref|id=Larson-2004|text=Larson 2004 pp. 221–243}}</ref> | |||
| The American biologist ], who had a background in ] experiments, focused on combinations of interacting genes, and the effects of inbreeding on small, relatively isolated populations that exhibited ]. In 1932, Wright introduced the concept of an ] 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 ]. This integrated natural selection with Mendelian genetics, which was the critical first step in developing a unified theory of how evolution worked.<ref name="Bowler325-339"/><ref name="Larson221-243"/> | |||
| ===Modern evolutionary synthesis=== | |||
| In the first few decades of the 20th century, most field naturalists continued to believe that Lamarckian and orthogenic mechanisms of evolution provided the best explanation for the complexity they observed in the living world. However, as the field of genetics continued to develop, those views became less tenable.<ref>{{wikiref|id=Mayr-1998|text= Mayr and Provine (1998) pp. 295–298, 416}}</ref> ], a postdoctoral worker in T. H. Morgan's lab, had been influenced by the work on genetic diversity by ]n geneticists such as ]. He helped to bridge the divide between the foundations of ] developed by the population geneticists and the patterns of ] observed by field biologists, with his 1937 book '']''. 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 ], the pioneer of ], continued throughout the 1930s and 1940s to demonstrate the power of selection due to ecological factors including the ability to maintain genetic diversity through ] such as human ]. Ford's work would contribute to a shift in emphasis during the course of the modern synthesis towards ] over ]. <ref name="Bowler325-339"/><ref name="Larson221-243"/><ref>{{cite book|author=Mayr, E§year=1988|title=Towards a new philosophy of biology: observations of an evolutionist|publisher=Harvard University Press|pages=402}}</ref><ref>{{wikiref|id=Mayr-1998|text= Mayr and Provine (1998) pp. 338–341}}</ref> | |||
| ] was influenced by the work of the German biologist ] on how local environmental factors influenced 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 ] 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 ]. Mayr also formulated the ] that defined a species as a group of interbreeding or potentially interbreeding populations that were reproductively isolated from all other populations.<ref name="Bowler325-339"/><ref name="Larson221-243"/><ref>{{wikiref|id=Mayr-1998|text= Mayr and Provine (1998) pp. 33–34}}</ref> | |||
| In the 1944 book '']'', ] 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, ] published '']'', which helped to integrate ] into the synthesis. The emerging cross-disciplinary consensus on the workings of evolution would be known as the ]. It received its name from the book '']'' by ].<ref name="Bowler325-339"/><ref name="Larson221-243"/> | |||
| 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.<ref>{{wikiref|id=Smocovitis-1996|text=Smocovitis 1996 pp. 97–188}}</ref> 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 (]), and macroevolution was simply considered the result of extensive microevolution.<ref>{{wikiref|id=Sapp-2003|text=Sapp 2003 pp. 152–156}}</ref><ref>{{Cite book|last=Gould|first=Stephen Jay|authorlink=Stephen Jay Gould|editor=Marjorie Grene|title=Dimensions of Darwinism|origdate=1983|chapter=The hardening of the modern synthesis|chapterurl=http://www.stephenjaygould.org/library/gould_synthesis.html|publisher=Cambridge University Press}}</ref> | |||
| ==1940s–1960s: Molecular biology and evolution== | |||
| {{main|History of molecular evolution}} | |||
| The middle decades of the 20th century saw the ], and with it an understanding of the chemical nature of genes as ] and their relationship, through the ], to ]s. At the same time, increasingly powerful techniques for analyzing proteins, such as ] and ], brought biochemical phenomena into realm of the synthetic theory of evolution. In the early 1960s, biochemists ] and ] proposed the ]: that sequence differences between ]s could be used to calculate the time since two species diverged. By 1969, ] 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 ], rather than ], is responsible for a large portion of genetic change: the ].<ref>{{Cite journal| doi = 10.1007/BF01058626| volume = 27| issue = 1| pages = 21–59| last = Dietrich| first = Michael R.| title = The origins of the neutral theory of molecular evolution| journal = Journal of the History of Biology| accessdate = 2008-07-27| date = 1994-03-01| doi = 10.1007/BF01058626}}</ref> Studies of protein differences ''within'' species also brought molecular data to bear on population genetics by providing estimates of the level of ] in natural populations.<ref>{{cite book|last=Powell|first=Jeffrey R|chapter=Molecular techniques in population genetics: A brief history|pages=131–156|title=Molecular Ecology and Evolution: Approaches and Applications|editor=B. Schierwater, B. Streit, G. P. Wagner, and R. De Salle (eds.)|publisher=Birkhäuser Verlag|origdate=1994|isbn=3-7643-2942-4}}</ref> | |||
| 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 ]. The molecular clock hypothesis and the neutral theory were particularly controversial, spawning the ] over the relative importance of drift and selection, which continued into the 1980s without a clear resolution.<ref>{{Cite journal| doi = 10.1023/A:1004257523100| volume = 31| issue = 1| pages = 85–111| last = Dietrich| first = Michael R.| title = Paradox and Persuasion: Negotiating the Place of Molecular Evolution within Evolutionary Biology| journal = Journal of the History of Biology| accessdate = 2008-07-27| date = 1998-03-01| doi = 10.1023/A:1004257523100}}</ref><ref>{{Cite journal| doi = 10.1023/A:1004660202226| volume = 32| issue = 2| pages = 321–341| last = Hagen| title = Naturalists, Molecular Biologists, and the Challenges of Molecular Evolution| journal = Journal of the History of Biology| accessdate = 2008-07-27| year = 1999| doi = 10.1023/A:1004660202226}}</ref> | |||
| ==Late 20th century== | |||
| ===Gene-centered view=== | |||
| In the mid-1960s, ] strongly critiqued explanations of adaptations worded in terms of "survival of the species" (] arguments). Such explanations were largely replaced by a ], epitomized by the ] arguments of ], ] and ].<ref>{{cite journal |author=Mayr E |title=The objects of selection |url=http://www.pnas.org/cgi/content/full/94/6/2091 |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=94 |issue=6 |pages=2091–94 |year=1997 |pmid=9122151 |doi=10.1073/pnas.94.6.2091}}</ref> This viewpoint would be summarized and popularized in the influential 1976 book '']'' by ].<ref>{{wikiref|id=Bowler-2003|text= Bowler 2003 p. 361}}</ref> Models of the period showed that group selection was severely limited in its strength; these models have since been shown to be too limited and newer models do admit the possibility of significant multi-level selection.<ref name=Gould>{{cite journal |author=Gould SJ |title=Gulliver's further travels: the necessity and difficulty of a hierarchical theory of selection |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=9533127 |journal=Philos. Trans. R. Soc. Lond., B, Biol. Sci. |volume=353 |issue=1366 |pages=307–14 |year=1998 |pmid=9533127 |doi=10.1098/rstb.1998.0211}}</ref> | |||
| In 1973, ] proposed the term "]", which he took from '']'' by ], to describe a scenario where a species involved in one or more ]s would have to constantly change just to keep pace with the species with which it was ]. Hamilton, Williams and others suggested that this idea might explain the ]: 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 ] is passed on during reproduction.<ref>{{wikiref|id=Larson 2004|text= Larson 2004 p. 279}}</ref><ref>{{wikiref|id=Bowler-2003|text= Bowler 2003 p. 358}}</ref> The gene-centric view has also led to an increased interest in Darwin's old idea of ],<ref>{{wikiref|id=Bowler-2003|text= Bowler 2003 pp. 358–359}}</ref> and more recently in topics such as ] and ]. | |||
| ===Sociobiology=== | |||
| W. D. Hamilton's work on kin selection contributed to the emergence of the discipline of ]. The existence of ] has been a difficult problem for evolutionary theorists from the beginning.<ref>{{cite journal |author=Sachs J |title=Cooperation within and among species |journal=J. Evol. Biol. |volume=19 |issue=5 |pages=1415–8; discussion 1426–36 |year=2006 |pmid=16910971 |doi=10.1111/j.1420-9101.2006.01152.x}}</ref> Significant progress was made in 1964 when Hamilton formulated the inequality in ] known as Hamilton's rule, which showed how ] 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 ], such as ].<ref>{{cite journal |author=Nowak M |title=Five rules for the evolution of cooperation |journal=Science |volume=314 |issue=5805 |pages=1560–63 |year=2006 |pmid=17158317 |doi=10.1126/science.1133755}}</ref> In 1975, ] published the influential and highly controversial book '']'' which claimed evolutionary theory could help explain many aspects of animal, including human, behavior. Critics of sociobiology, including ] and ], 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 ], including work on other aspects of the altruism problem.<ref>{{wikiref|id=Larson-2004|text=Larson 2004 pp. 270–278}}</ref><ref>{{wikiref|id=Bowler-2003|text=Bowler 2003 pp. 359–361}}</ref> | |||
| ] showing the ]. ]s are colored red, ] green, and ] blue.]] | |||
| ===Evolutionary paths and processes=== | |||
| One of the most prominent debates arising during the 1970s was over the theory of ]. ] and ] 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 ].<ref name=pe1972>Niles Eldredge and Stephen Jay Gould, 1972. In T.J.M. Schopf, ed., ''Models in Paleobiology''. San Francisco: Freeman Cooper. pp. 82–115. Reprinted in N. Eldredge ''Time frames''. Princeton: Princeton Univ. Press. 1985</ref><ref>{{cite journal |author=Gould SJ |title=Tempo and mode in the macroevolutionary reconstruction of Darwinism |url=http://www.pnas.org/cgi/reprint/91/15/6764 |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=91 |issue=15 |pages=6764–71 |year=1994 |pmid=8041695 |doi=10.1073/pnas.91.15.6764}}</ref> Improvements in ] methods resulted in a large increase of sequenced ]s, allowing the testing and refining of evolutionary theories using this huge amount of genome data.<ref>{{cite journal |author=Pollock DD, Eisen JA, Doggett NA, Cummings MP |title=A case for evolutionary genomics and the comprehensive examination of sequence biodiversity |journal=Mol. Biol. Evol. |volume=17 |issue=12 |pages=1776–88 |year=2000 |pmid=11110893 |url=http://mbe.oxfordjournals.org/cgi/content/full/17/12/1776}}</ref> Comparisons between these genomes provide insights into the molecular mechanisms of speciation and adaptation.<ref>{{cite journal |author=Koonin EV |title=Orthologs, paralogs, and evolutionary genomics |journal=Annu. Rev. Genet. |volume=39 |pages=309–38 |year=2005 |pmid=16285863 |doi=10.1146/annurev.genet.39.073003.114725}}</ref><ref>{{cite journal |author=Hegarty MJ, Hiscock SJ |title=Hybrid speciation in plants: new insights from molecular studies |journal=New Phytol. |volume=165 |issue=2 |pages=411–23 |year=2005 |pmid=15720652 |doi=10.1111/j.1469-8137.2004.01253.x}}</ref> These genomic analyses have produced fundamental changes in the understanding of the ], such as the creation of the ] by ].<ref name=Woese>{{cite journal |author=Woese C, Kandler O, Wheelis M |title=Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya | url=http://www.pnas.org/cgi/reprint/87/12/4576 |journal=Proc Natl Acad Sci U S A |volume=87 |issue=12 |pages=4576–79 |year=1990 |pmid=2112744 |doi=10.1073/pnas.87.12.4576}}</ref> Advances in computational hardware and software allow the testing and extrapolation of increasingly advanced evolutionary ] and the development of the field of ].<ref>{{cite journal |author=Medina M |title=Genomes, phylogeny, and evolutionary systems biology |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=102 Suppl 1 |pages=6630–5 |year=2005 |pmid=15851668 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15851668 |doi=10.1073/pnas.0501984102}}</ref> One of the results has been an exchange of ideas between theories of biological evolution and the field of ] known as ], which attempts to mimic biological evolution for the purpose of developing new computer ]. Discoveries in ] now allow the modification of genomes, driving evolutionary studies to the level where future experiments may involve the creation of entirely synthetic organisms.<ref>{{cite journal |author=Benner SA, Sismour AM |title=Synthetic biology |journal=Nat. Rev. Genet. |volume=6 |issue=7 |pages=533–43 |year=2005 |pmid=15995697 |doi=10.1038/nrg1637}}</ref> | |||
| ===Microbiology and horizontal gene transfer=== | |||
| {{main|Horizontal gene transfer}} | |||
| ] 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 ]s.<ref>{{cite journal |author=Gevers D, Cohan FM, Lawrence JG, ''et al'' |title=Opinion: Re-evaluating prokaryotic species |journal=Nat. Rev. Microbiol. |volume=3 |issue=9 |pages=733–9 |year=2005 |pmid=16138101 |doi=10.1038/nrmicro1236}}</ref> Now, evolutionary researchers are taking advantage their improved understanding of microbial physiology and ecology, produced by the comparative ease of microbial ], to explore the taxonomy and evolution of these organisms.<ref>{{cite journal |author=Coenye T, Gevers D, Van de Peer Y, Vandamme P, Swings J |title=Towards a prokaryotic genomic taxonomy |journal=FEMS Microbiol. Rev. |volume=29 |issue=2 |pages=147–67 |year=2005 |pmid=15808739 |doi=10.1016/j.femsre.2004.11.004}}</ref> These studies are revealing completely unanticipated levels of diversity amongst microbes, demonstrating that these organisms are the dominant form of life on Earth.<ref>{{cite journal |author=Whitman W, Coleman D, Wiebe W |title=Prokaryotes: the unseen majority |url=http://www.pnas.org/cgi/content/full/95/12/6578 |journal=Proc Natl Acad Sci U S A |volume=95 |issue=12 |pages=6578–83 |year=1998|pmid=9618454 |doi=10.1073/pnas.95.12.6578}}</ref><ref name=Schloss>{{cite journal |author=Schloss P, Handelsman J |title=Status of the microbial census |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15590780#r6 |journal=Microbiol Mol Biol Rev |volume=68 |issue=4 |pages=686–91 |year=2004 |pmid=15590780 |doi=10.1128/MMBR.68.4.686-691.2004}}</ref> | |||
| One particularly important outcome from studies on microbial evolution was the discovery in Japan of ] in 1959.<ref>{{cite journal |author=Ochiai K, Yamanaka T, Kimura K Sawada O |title=Inheritance of drug resistance (and its transfer) between Shigella strains and Between Shigella and E.coli strains |journal=Hihon Iji Shimpor |volume=1861 |pages=34 |year=1959}} (in Japanese)</ref> This transfer of genetic material between different species of bacteria has played a major role in the propagation of ].<ref>{{cite web|title=Lateral gene transfer and the nature of bacterial innovation|url=http://www.stat.rice.edu/~mathbio/Ochman2000.pdf|format=PDF|publisher=Nature Vol 405, May 18 2000|accessdate=2007-09-01}}</ref> More recently, as knowledge of ]s 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.<ref>{{cite journal |author=de la Cruz F, Davies J |title=Horizontal gene transfer and the origin of species: lessons from bacteria |journal=Trends Microbiol. |volume=8 |issue=3 |pages=128–33 |year=2000 |pmid=10707066 |doi=10.1016/S0966-842X(00)01703-0}}</ref> Indeed, as part of the ] for the origin of ]s, horizontal gene transfer has been a critical step in the evolution of ]s such as fungi, plants, and animals.<ref>{{cite journal |author=Poole A, Penny D |title=Evaluating hypotheses for the origin of eukaryotes |journal=Bioessays |volume=29 |issue=1 |pages=74–84 |year=2007 |pmid=17187354 |doi=10.1002/bies.20516}}</ref><ref name=Dyall>{{cite journal |author=Dyall S, Brown M, Johnson P |title=Ancient invasions: from endosymbionts to organelles |journal=Science |volume=304 |issue=5668 |pages=253–7 |year=2004 |pmid=15073369 |doi=10.1126/science.1094884}}</ref> | |||
| ===Evolutionary developmental biology=== | |||
| {{main|Evolutionary developmental biology}} | |||
| In the 1980s and 1990s the tenets of the ] came under increasing scrutiny. There was a renewal of ] themes in evolutionary biology in the work of biologists such as ] and ], which incorporated ideas from ] and ], and emphasized the ] processes of development as factors directing the course of evolution. The evolutionary biologist ] revived earlier ideas of ], 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 ], 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 "]" after an architectural feature.<ref>{{cite journal |author=Gould SJ |title=The exaptive excellence of spandrels as a term and prototype |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=94 |issue=20 |pages=10750–5 |year=1997 |pmid=11038582 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=11038582 |doi=10.1073/pnas.94.20.10750}}</ref> Later, Gould and Vrba discussed the acquisition of new functions by novel structures arising in this fashion, calling them "]s".<ref>{{cite journal |author=Gould SJ and Vrba ES|title=Exaptation — a missing term in the science of form |journal=Paleobiology |volume=8 |issue=1 |pages=4–15 |year=1982}}</ref> | |||
| Molecular data regarding the mechanisms underlying ] 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.<ref>{{cite journal |author=True JR, Carroll SB |title=Gene co-option in physiological and morphological evolution |journal=Annu. Rev. Cell Dev. Biol. |volume=18 |pages=53–80 |year=2002 |pmid=12142278 |doi=10.1146/annurev.cellbio.18.020402.140619}}</ref> These proteins became known as the ].<ref>{{cite journal |author=Cañestro C, Yokoi H, Postlethwait JH |title=Evolutionary developmental biology and genomics |journal=Nat Rev Genet |volume=8 |issue=12 |pages=932–942 |year=2007 |pmid=18007650 |doi=10.1038/nrg2226}}</ref> Such perspectives influenced the disciplines of ], ] and comparative developmental biology, and spawned the new discipline of "evo-devo".<ref>{{cite journal |author=Baguñà J, Garcia-Fernàndez J |title=Evo-Devo: the long and winding road |url=http://www.ijdb.ehu.es/web/paper.php?doi=14756346 |journal=Int. J. Dev. Biol. |volume=47 |issue=7–8 |pages=705–13 |year=2003 |pmid=14756346}}<br />*{{cite journal |author=Gilbert SF |title=The morphogenesis of evolutionary developmental biology |journal=Int. J. Dev. Biol. |volume=47 |issue=7–8 |pages=467–77 |year=2003 |pmid=14756322}}</ref> | |||
| More recent work in this field has emphasized ]<ref>{{cite book | author= West-Eberhard, M-J | year=2003 | title=Developmental Plasticity and Evolution | publisher=Oxford University Press}}</ref>. It has been suggested, for example, that the rapid emergence of basic animal body plans in the ] was due in part to changes in the environment acting on inherent material properties of cell aggregates, such as differential ] and ]. The resulting forms were later stabilized by natural selection.<ref>{{cite journal |author=Newman SA, Müller GB |title=Epigenetic mechanisms of character origination |journal=J. Exp. Zool. B Mol. Develop. Evol. |volume=288 |pages=304–17 |year=2000 |pmid=11144279 |doi=10.1002/1097-010X(20001215)288:4}}</ref> Experimental and theoretical research on these and related ideas have been presented in the multi-authored volume '']''. | |||
| ==Unconventional evolutionary theory== | |||
| ===Omega point=== | |||
| <!-- {{main|Omega point}} --> | |||
| ]'s non-scientific ] describes the gradual development of the ] from subatomic particles to human society, which he viewed as its final stage and goal. | |||
| ===Gaia hypothesis=== | |||
| <!-- {{main|Gaia hypothesis}} --> | |||
| Teilhard de Chardin's ideas have been seen as being connected to the more specific ] by ], who proposed that the living and nonliving parts of Earth can be viewed as a complex interacting system with similarities to a single organism.<ref>{{cite journal |author=Lovelock J |title=Gaia: the living Earth |journal=Nature |volume=426 |issue=6968 |pages=769–70 |year=2003 |pmid=14685210 |doi=10.1038/426769a}}</ref> The Gaia hypothesis has also been viewed by ],<ref>{{cite web|last=Margulis|first =Lynn|title =Gaia Is a Tough Bitch|publisher=The Third Culture|year=1995|url=http://www.edge.org/documents/ThirdCulture/n-Ch.7.html|accessdate=2007-09-30}}</ref> and others as an extension of ] and ].<ref>{{cite journal|author=Fox, Robin|year=2004|title=Symbiogenesis.|journal=Journal of the royal society of medicine|volume=97|issue=12|pages=p. 559|doi=10.1258/jrsm.97.12.559|url=http://jrsm.rsmjournals.com/cgi/content/full/97/12/559}}</ref> This modified hypothesis postulates that all living things have a regulatory effect on the Earth's environment that promotes life overall. | |||
| ===Transhumanism=== | |||
| <!-- {{main|Transhumanism|Technological singularity}} --> | |||
| ] have often viewed scientific and technological progress as a continuation of biological evolution. Among these, ] often view such technological evolution itself as a goal in their philosophy, possibly in the form of a ]. | |||
| ==See also== | |||
| {{Portal|Evolutionary biology|Tree_of_life.svg}} | |||
| * ] | |||
| * ] | |||
| * ] | |||
| ==Notes== | |||
| {{reflist|2}} | |||
| ==References== | |||
| * {{cite book|last=Bowler|first=Peter J.|authorlink=Peter J. Bowler|title=Evolution: The History of an Idea|edition=3rd edition|publisher=University of California Press|year=2003|isbn=0-52023693-9}} | |||
| * {{cite book|last=Bowler|first=Peter J.|coauthors=Iwan Rhys Morus|title=Making Modern Science|publisher=The University of Chicago Press|year=2005|isbn=0-226-06861-7}} | |||
| * {{cite book|last=Darlington|first=Cyril|authorlink=Cyril Darlington|title=Darwin's place in history|publisher=Blackwell, Oxford, p85|year=1959}} | |||
| * {{cite book|last=Darwin|first=Charles|authorlink=Charles Darwin|title=] by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life|edition=1st|publisher=John Murray, London|year=1859}} | |||
| * {{cite book|last=Darwin|first=Charles|authorlink=Charles Darwin|title=] by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life|edition=3rd|publisher=John Murray, London|year=1861}} | |||
| * {{cite book|last=Darwin|first=Charles|authorlink=Charles Darwin|title=] by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life|edition=4th|publisher=John Murray, London|year=1866}} | |||
| * {{cite book|last=Darwin|first=Charles|authorlink=Charles Darwin|title=] by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life|edition=6th|publisher=John Murray, London|year=1872}} | |||
| *{{cite book|last=Darwin|first=Erasmus|authorlink=Erasmus Darwin|year=1825|title=The Temple of Nature, or The Origin of Society|url=http://books.google.com/books?id=oAl9y-0FSJQC&dq=Erasmus+Darwin+Temple}} | |||
| *{{cite book|last=Darwin|first=Erasmus|year=1818|title=Zoonomia|url=http://www.gutenberg.org/files/15707/15707-h/15707-h.htm}} | |||
| *{{cite book|last=Desmond|first=Adrian|coauthors=James Moore|title=Darwin: The Life of a Tormented Evolutionist |publisher=W. W. Norton & Company|year=1994|isbn=0393311503}} | |||
| *{{cite book|last=Draper|first=John William|authorlink=John William Draper|year=1878|title=History of the Conflict Between Religion and Science|url=http://books.google.com/books?id=0XolqaWimmkC&dq=John+William+Draper}} | |||
| *{{cite book|last=Gould|first=Stephen Jay|authorlink=Stephen Jay Gould|title=The Structure of Evolutionary Theory|publisher=Belknap Press of Harvard University Press|year=2002|isbn=0-674-00613-5}} | |||
| *{{cite book|last=Henderson|first=Jan-Andrew|title=The Emperor's Kilt: The Two Secret Histories of Scotland|publisher=Mainstream Publishing|year=2000}} | |||
| *{{cite book|last=Larson|first=Edward J.|authorlink=Edward Larson|title=Evolution: The Remarkable History of a Scientific Theory|publisher=Modern Library|year=2004|isbn=0-679-64288-9}} | |||
| *{{cite book|last=Lovejoy|first=Arthur|authorlink=Arthur Oncken Lovejoy|title=The Great Chain of Being: A Study of the History of an Idea|publisher=Harvard University Press|year=1936|isbn=0-674-36153-9}} | |||
| *{{cite book|last=Mayr|first=Ernst|authorlink=Ernst Mayr|title=The Growth of Biological Thought: Diversity, Evolution, and Inheritance|publisher=The Belknap Press of Harvard University Press|year=1982|isbn=0-674-36445-7}} | |||
| *{{cite book|last=Mayr|first=Ernst|coauthors=W. B. Provine, eds.|title=The Evolutionary Synthesis: Perspectives on the Unification of Biology|publisher=Harvard University Press|year=1998|isbn=0-674-27225-0}} | |||
| *{{cite book|last=Needham|first=Joseph|authorlink=Joseph Needham|coauthors=Colin Alistair Ronan|title=The Shorter Science and Civilisation in China: An Abridgement of Joseph Needham's Original Text, Vol. 1|publisher=Cambridge University Press|year=1995|isbn=0521292867}} | |||
| *{{cite book|last=Sapp|first=Jan|title=Genesis: The Evolution of Biology|publisher=Oxford University Press|year=2003|isbn=0-19-515618-8}} | |||
| *{{cite book|last=Secord|first=James A.|title=Victorian Sensation: The Extraordinary Publication, Reception, and Secret Authorship of Vestiges of the Natural History of Creation|publisher=University of Chicago Press|year=2000|isbn=0-226-74410-8}} | |||
| *{{cite book|last=Singer|first=Charles|authorlink=Charles Singer|title=A Short History of Biology|publisher=Clarendon Press|year=1931}} | |||
| *{{cite book|last=Smocovitis|first=Vassiliki Betty|title=Unifying Biology: The Evolutionary Synthesis and Evolutionary Biology|publisher=Princeton University Press|year=1996|isbn=0-691-03343-9}} | |||
| ==External links== | |||
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