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These alternative terms are ambiguous as they could possibly include later syntheses, so this article uses [[Julian Huxley]]'s 1942 "modern synthesis"{{sfn|Huxley|2010}} throughout.}} was the early 20th-century synthesis of [[Charles Darwin]]'s theory of [[evolution]] and [[Gregor Mendel]]'s ideas on heredity into a joint mathematical framework. [[Julian Huxley]] coined the term in his 1942 book, ''[[Evolution: The Modern Synthesis]]''. The synthesis combined the ideas of [[natural selection]], [[Mendelian inheritance|Mendelian genetics]], and [[population genetics]]. It also related the broad-scale [[macroevolution]] seen by [[paleontology|palaeontologists]] to the small-scale [[microevolution]] of local [[population|populations.]] The synthesis was defined differently by its founders, with [[Ernst Mayr]] in 1959, [[G. Ledyard Stebbins]] in 1966, and [[Theodosius Dobzhansky]] in 1974 offering differing basic postulates, though they all include natural selection, working on heritable variation supplied by mutation. Other major figures in the synthesis included [[E. B. Ford]], [[Bernhard Rensch]], [[Ivan Schmalhausen]], and [[George Gaylord Simpson]]. An early event in the modern synthesis was [[R. A. Fisher]]'s 1918 paper on mathematical population genetics, though [[William Bateson]], and separately [[Udny Yule]], had already started to show how Mendelian genetics could work in evolution in 1902. Different syntheses followed, including with [[social behaviour]] in [[E. O. Wilson]]'s [[sociobiology]] in 1975, [[evolutionary developmental biology]]'s integration of [[embryology]] with genetics and evolution, starting in 1977, and [[Massimo Pigliucci]]'s and [[Gerd B. Müller]]'s proposed [[extended evolutionary synthesis]] of 2007. In the view of evolutionary biologist [[Eugene Koonin]] in 2009, the modern synthesis will be replaced by a 'post-modern' synthesis that will include revolutionary changes in [[molecular biology]], the study of [[prokaryote]]s and the resulting [[tree of life (biology)|tree of life]], and [[genomics]].<ref name=Koonin2009 /> ==Developments leading up to the synthesis== [[File:Darwin's Pangenesis.svg|thumb|upright=1.35|[[Charles Darwin|Darwin]]'s [[pangenesis]] theory. Every part of the body emits tiny gemmules which migrate to the [[gonad]]s and contribute to the next generation via the fertilised egg. Changes to the body during an organism's life would be inherited, as in [[Lamarckism]].]] {{further|History of evolutionary thought}} ===Darwin's evolution by natural selection, 1859=== {{main|Evolution|Natural selection}} [[Charles Darwin]]'s 1859 book, ''[[On the Origin of Species]],'' convinced most biologists that [[evolution]] had occurred, but not that [[natural selection]] was its primary mechanism. In the 19th and early 20th centuries, variations of [[Lamarckism]] (inheritance of acquired characteristics), [[orthogenesis]] (progressive evolution), [[saltationism]] (evolution by jumps) and [[mutationism]] (evolution driven by mutations) were discussed as alternatives.<ref>{{harvnb|Bowler|2003|pp=236–256}}</ref> Darwin himself had sympathy for Lamarckism, but [[Alfred Russel Wallace]] advocated natural selection and totally rejected Lamarckism.<ref>{{cite journal |last=Kutschera |first=Ulrich |author-link=Ulrich Kutschera |date=December 2003 |title=A comparative analysis of the Darwin–Wallace papers and the development of the concept of natural selection |journal=Theory in Biosciences |volume=122 |issue=4 |pages=343–359 |doi=10.1007/s12064-003-0063-6|s2cid=24297627 }}</ref> In 1880, Samuel Butler labelled Wallace's view [[neo-Darwinism]].<ref>{{cite book |last1=Butler |first1=Samuel |author-link1=Samuel Butler (novelist)|title=Unconscious Memory |date=1880 |publisher=David Bogue |page=280 |url=https://archive.org/details/unconsciousmemo00hartgoog |quote=I may predict with some certainty that before long we shall find the original Darwinism of Dr. [[Erasmus Darwin]] … generally accepted instead of the neo-Darwinism of to-day, and that the variations whose accumulation results in species will be recognised as due to the wants and endeavours of the living forms in which they appear, instead of being ascribed to chance, or, in other words, to unknown causes, as by Mr. Charles Darwin's system}}</ref><ref>{{cite web |url=http://wallacefund.info/terms-darwinism-and-neo-darwinism |title=On the Terms "Darwinism" and "Neo-Darwinism" |last=Beccaloni |first=George |date=2013 |website=A. R. Wallace Website |access-date=2017-09-14 |archive-date=2019-04-11 |archive-url=https://web.archive.org/web/20190411231439/http://wallacefund.info/terms-darwinism-and-neo-darwinism |url-status=dead }}</ref> [[File:Blending Inheritance.svg|thumb|upright=1.1|[[Blending inheritance]], implied by pangenesis, causes the [[mean|averaging out]] of every characteristic, which as the engineer [[Fleeming Jenkin]] pointed out, would make evolution by [[natural selection]] impossible.]] ===The eclipse of Darwinism, 1880s onwards=== {{main|The eclipse of Darwinism}} From the 1880s onwards, biologists grew skeptical of Darwinian evolution. This [[eclipse of Darwinism]] (in [[Julian Huxley]]'s words) grew out of the weaknesses in Darwin's account, with respect to his view of inheritance. Darwin believed in [[blending inheritance]], which implied that any new variation, even if beneficial, would be weakened by 50% at each generation, as the engineer [[Fleeming Jenkin]] noted in 1868.<ref name="Bowler196-250">{{harvnb|Bowler|2003|pp=196–253}}</ref><ref name="Larson105-129">{{harvnb|Larson|2004|pp=105–129}}</ref> This in turn meant that small variations would not survive long enough to be selected. Blending would therefore directly oppose natural selection. In addition, Darwin and others considered Lamarckian inheritance of acquired characteristics entirely possible, and Darwin's 1868 theory of [[pangenesis]], with contributions to the next generation (gemmules) flowing from all parts of the body, actually implied Lamarckism as well as blending.<ref>{{cite book |author=Gayon, Jean |date=1998 |title=Darwinism's Struggle for Survival: Heredity and the Hypothesis of Natural Selection |publisher=Cambridge University Press |pages=2–3 |isbn=978-0-521-56250-8}}</ref><ref name="Darwin68">{{cite book | last=Darwin | first=Charles | author-link=Charles Darwin | year=1868 | title=The variation of animals and plants under domestication | publisher=John Murray | url=http://darwin-online.org.uk/content/frameset?itemID=F880.1&viewtype=text&pageseq=1 | isbn=978-1-4191-8660-8}}</ref><ref>{{cite journal |author=Holterhoff, Kate |date=2014 |title=The History and Reception of Charles Darwin's Hypothesis of Pangenesis |journal=Journal of the History of Biology |volume=47 |issue=4 |pages=661–695 |doi=10.1007/s10739-014-9377-0|pmid=24570302 |s2cid=207150548 }}</ref> [[File:Weismann's Germ Plasm.svg|thumb|upright=1.35|[[August Weismann]]'s [[germ plasm]] theory. The hereditary material, the germplasm, is confined to the [[gonad]]s and the [[gamete]]s. Somatic cells (of the body) [[embryology|develop]] afresh in each generation from the germplasm.]] ===Weismann's germ plasm, 1892=== {{main|Germ plasm}} [[August Weismann]]'s idea, set out in his 1892 book ''Das Keimplasma: eine Theorie der Vererbung'' ("The Germ Plasm: a Theory of Inheritance"),<ref>{{cite book |author=Weismann, August |date=1892 |title=Das Keimplasma: eine Theorie der Vererbung |trans-title=The Germ Plasm: A theory of inheritance |publisher=Fischer |location=Jena |url=http://www.deutschestextarchiv.de/book/show/weismann_keimplasma_1892}}</ref> was that the hereditary material, which he called the [[germ plasm]], and the rest of the body (the [[Somatic (biology)|soma]]) had 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. If correct, this made Darwin's pangenesis wrong, and Lamarckian inheritance impossible. His experiment on mice, cutting off their tails and showing that their offspring had normal tails, demonstrated that inheritance was 'hard'.{{efn|Peter Gauthier has however argued that [[Weismann's experiment]] showed only that injury did not affect the germplasm. It did not test the effect of Lamarckian use and disuse.<ref>{{cite journal |last=Gauthier |first=Peter |date=March–May 1990 |title=Does Weismann's Experiment Constitute a Refutation of the Lamarckian Hypothesis? |journal=BIOS |volume=61 |number=1/2 |pages=6–8 |jstor=4608123}}</ref>}} He argued strongly and dogmatically{{sfn|Bowler|1989|p=248}} for Darwinism and against Lamarckism, polarising opinions among other scientists. This increased anti-Darwinian feeling, contributing to its eclipse.<ref>{{harvnb|Bowler|2003|pp=253–256}}</ref>{{sfn|Bowler|1989|pp=247–253, 257}} ==Disputed beginnings== ===Genetics, mutationism and biometrics, 1900–1918=== {{main|Mutationism|Biostatistics}} [[File:William Bateson.jpg|thumb|upright|left|[[William Bateson]] championed [[Mendelian inheritance|Mendelism]].]] While carrying out breeding experiments to clarify the mechanism of inheritance in 1900, [[Hugo de Vries]] and [[Carl Correns]] independently rediscovered [[Gregor Mendel]]'s work. News of this reached [[William Bateson]] in [[England]], who reported on the paper during a presentation to the [[Royal Horticultural Society]] in May 1900.<ref>{{cite web |url=https://www.jic.ac.uk/germplas/PISUM/ZGS4F.HTM |title=Mendel's Peas |last=Ambrose |first=Mike |publisher=Germplasm Resources Unit, [[John Innes Centre]] |location=Norwich, UK |access-date=14 December 2017 |archive-url=https://web.archive.org/web/20160614210558/https://www.jic.ac.uk/germplas/PISUM/ZGS4F.HTM |archive-date=14 June 2016 |url-status=dead }}</ref> In [[Mendelian inheritance]], the contributions of each parent retain their integrity, rather than blending with the contribution of the other parent. In the case of a cross between two true-breeding varieties such as Mendel's round and wrinkled peas, the first-generation offspring are all alike, in this case, all round. Allowing these to cross, the original characteristics reappear (segregation): about 3/4 of their offspring are round, 1/4 wrinkled. There is a discontinuity between the appearance of the offspring; de Vries coined the term [[allele]] for a variant form of an [[gene|inherited characteristic]].<ref>{{cite web |title=Reviewing Mendel's Laws |url=http://www.phschool.com/science/biology_place/biocoach/inheritance/laws.html |publisher=Pearson |access-date=14 October 2017}}</ref> This reinforced a major division of thought, already present in the 1890s, between gradualists who followed Darwin, and saltationists such as Bateson.<ref>{{harvnb|Bateson|1894}}: Mutations (as 'sports') and polymorphisms were well known long before the Mendelian recovery.</ref> The two schools were the Mendelians, such as Bateson and de Vries, who favoured mutationism, evolution driven by mutation, based on genes whose alleles [[Particulate inheritance|segregated discretely]] like Mendel's peas;<ref>{{harvnb|Larson|2004|pp=157–166}}</ref><ref>{{harvnb|Bowler|1989|pp=275–276}}</ref> and the [[Biostatistics|biometric school]], led by [[Karl Pearson]] and [[Walter Frank Raphael Weldon|Walter Weldon]]. The biometricians argued vigorously against mutationism, saying that empirical evidence indicated that variation was continuous in most organisms, not discrete as Mendelism seemed to predict; they wrongly believed that Mendelism inevitably implied evolution in discontinuous jumps.<ref name="grafen 69"/><ref>{{harvnb|Provine|2001|p=69}}</ref> [[File:Karl Pearson, 1912.jpg|thumb|upright|[[Karl Pearson]] led the [[Biostatistics|biometric school]].]] A traditional view is that the biometricians and the Mendelians rejected natural selection and argued for their separate theories for 20 years, the debate only resolved by the development of population genetics.<ref name="grafen 69">{{harvnb|Grafen|Ridley|2006|p=69}}</ref><ref>{{cite journal |last1=Olby |first1=Robert |title=The Dimensions of Scientific Controversy: The Biometric-Mendelian Debate |journal=[[The British Journal for the History of Science]] |date=September 1989 |volume=22 |issue=3 |pages=299–320 |jstor=4026898 |doi=10.1017/s0007087400026170|pmid=11621982 |s2cid=36719974 }}</ref> A more recent view is that Bateson, de Vries, [[Thomas Hunt Morgan]] and [[Reginald Punnett]] had by 1918 formed a synthesis of Mendelism and mutationism. The understanding achieved by these geneticists spanned the action of natural selection on alleles (alternative forms of a gene), the [[Hardy–Weinberg equilibrium]], the evolution of continuously varying traits (like height), and the probability that a new mutation will become fixed. In this view, the early geneticists accepted natural selection but rejected Darwin's non-Mendelian ideas about variation and heredity, and the synthesis began soon after 1900.<ref>{{cite book | author=Gayon, J. | title=Darwinism's Struggle for Survival: Heredity and the Hypothesis of Natural Selection |year=1988 | publisher=Cambridge University Press}}</ref><ref name="Stoltzfus">{{cite journal |last1=Stoltzfus |first1=Arlin |last2=Cable |first2=Kele |title=Mendelian-Mutationism: The Forgotten Evolutionary Synthesis |journal=[[Journal of the History of Biology]] |date=2014 |volume=47 |issue=4 |pages=501–546 |doi=10.1007/s10739-014-9383-2 |url=https://link.springer.com/content/pdf/10.1007%2Fs10739-014-9383-2.pdf |archive-url=https://web.archive.org/web/20141130175754/http://link.springer.com/content/pdf/10.1007%2Fs10739-014-9383-2.pdf |archive-date=2014-11-30 |url-status=live |pmid=24811736|s2cid=23263558 |doi-access=free }}</ref> The traditional claim that Mendelians rejected the idea of continuous variation is false; as early as 1902, Bateson and Saunders wrote that "If there were even so few as, say, four or five pairs of possible allelomorphs, the various homo- and heterozygous combinations might, on seriation, give so near an approach to a continuous curve, that the purity of the elements would be unsuspected".<ref name="BatesonSaunders1902">{{cite journal |last1=Bateson |first1=William |author1-link=William Bateson |last2=Saunders |first2=E. R. |author2-link=Edith Rebecca Saunders |title=Experimental Studies in the Physiology of Heredity |journal=Royal Society. Reports to the Evolution Committee |date=1902 |url=http://post.queensu.ca/~forsdyke/bateson1.htm#Bateson%20&%20Saunders%20(1902) |access-date=2017-08-20 |archive-date=2020-04-23 |archive-url=https://web.archive.org/web/20200423144636/http://post.queensu.ca/~forsdyke/bateson1.htm#Bateson%20&%20Saunders%20(1902) |url-status=dead }}</ref> Also in 1902, the statistician [[Udny Yule]] showed mathematically that given multiple factors, Mendel's theory enabled continuous variation. Yule criticised Bateson's approach as confrontational,<ref>{{cite journal | last1=Yule | first1=G. Udny |author-link=Udny Yule | title=Mendel's Laws and their probable relations to inter-racial heredity |url=http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.1902.tb06590.x/pdf |journal=[[New Phytologist]] |volume=1 | issue=10 |pages=226–227 |date=1902 | doi=10.1111/j.1469-8137.1902.tb07336.x|doi-access=free }}</ref> but failed to prevent the Mendelians and the biometricians from falling out.{{sfn|Provine|2001|pp=81–82}} ===Castle's hooded rats, 1911=== Starting in 1906, [[William Ernest Castle|William Castle]] carried out a long study of the effect of selection on coat colour in [[rat]]s. The [[piebald]] or hooded pattern was [[recessive]] to the grey wild type. He crossed hooded rats with both wild and "Irish" types, and then back-crossed the offspring with pure hooded rats. The dark stripe on the back was bigger. He then tried selecting different groups for bigger or smaller stripes for 5 generations and found that it was possible to change the characteristics considerably beyond the initial range of variation. This effectively refuted de Vries's claim that continuous variation was caused by the environment and could not be inherited. By 1911, Castle noted that the results could be explained by Darwinian selection on a heritable variation of a sufficient number of Mendelian genes.{{sfn|Provine|2001|pp=109–114}}<ref>{{cite journal|last=Castle |first=W. E. |date=7 April 1905 |title=The Mutation Theory of Organic Evolution, from the Standpoint of Animal Breeding |url=http://dx.doi.org/10.1126/science.21.536.521 |journal=[[Science (journal)|Science]] |volume=21 |issue=536 |pages=521–525 |doi=10.1126/science.21.536.521 |pmid=17770959 |bibcode=1905Sci....21..521C |issn=0036-8075}}</ref><ref>{{cite book |last=Vicedo |first=Marga |title=Castle, William Ernest (1867-1962), biologist |year=2000 |publisher=[[Oxford University Press]] |series=American National Biography Online |doi=10.1093/anb/9780198606697.article.1302308}}</ref> ===Morgan's fruit flies, 1912=== {{main|Thomas Hunt Morgan}} Thomas Hunt Morgan began his career in genetics as a [[Saltation (biology)|saltationist]] and started out trying to demonstrate that mutations could produce new species in fruit flies. However, the experimental work at his lab with the fruit fly, ''[[Drosophila melanogaster]]''{{efn|Morgan's work with fruit flies helped establish the link between Mendelian genetics and the [[chromosome|chromosomal]] theory of inheritance, that the hereditary material was embodied in these bodies within the cell nucleus.<ref name="auto">{{harvnb|Bowler|2003|pp=271–272}}</ref>}} showed that rather than creating new species in a single step, mutations increased the supply of genetic variation in the population.<ref name="auto"/> By 1912, after years of work on the genetics of fruit flies, Morgan showed that these insects had many small Mendelian factors (discovered as mutant flies) on which Darwinian evolution could work as if the variation was fully continuous. The way was open for geneticists to conclude that Mendelism supported Darwinism.{{sfn|Provine|2001|pp=120–121}} {{anchor|Woodger}} ==An obstruction: Woodger's positivism, 1929== {{further|Joseph Henry Woodger}} The [[theoretical biology|theoretical biologist]] and [[philosophy of biology|philosopher of biology]] [[Joseph Henry Woodger]] led the introduction of [[logical positivism|positivism]] into biology with his 1929 book ''Biological Principles''. He saw a mature [[science]] as being characterised by a framework of [[hypothesis|hypotheses]] that could be verified by facts established by [[experiment]]s. He criticised the traditional [[natural history]] style of [[biology]], including the study of [[evolution]], as immature science, since it relied on [[narrative]].<ref name=Smocovitis100>{{harvnb|Smocovitis|1996|pp=100–114}}</ref> Woodger set out to play the role of [[Robert Boyle]]'s 1661 ''[[Sceptical Chymist]]'', intending to convert the subject of biology into a formal, unified science, and ultimately, following the [[Vienna Circle]] of logical positivists like [[Otto Neurath]] and [[Rudolf Carnap]], [[reductionism|to reduce]] biology to physics and chemistry. His efforts stimulated the biologist [[J. B. S. Haldane]] to push for the axiomatisation of biology, and by influencing thinkers such as Huxley, helped to bring about the modern synthesis.<ref name=Smocovitis100/> The positivist climate made natural history unfashionable, and in America, research and university-level teaching on evolution declined almost to nothing by the late 1930s. The Harvard physiologist [[William John Crozier]] told his students that evolution was not even a science: "You can't experiment with two million years!"<ref name=Smocovitis114>{{harvnb|Smocovitis|1996|pp=114–119}}</ref> The tide of opinion turned with the adoption of [[mathematical model]]ling and [[controlled experiment]]ation in population genetics, combining genetics, ecology and evolution in a framework acceptable to positivism.<ref name=Smocovitis119>{{harvnb|Smocovitis|1996|pp=119–122}}</ref> ==Elements of the synthesis== ===Fisher and Haldane's mathematical population genetics, 1918–1930=== {{main|A Mathematical Theory of Natural and Artificial Selection}} In 1918, R. A. Fisher wrote "[[The Correlation between Relatives on the Supposition of Mendelian Inheritance]],"<ref>{{cite journal |last=Fisher |first=Ronald A. |author-link=Ronald Fisher |date=January 1919 |title=XV.—The Correlation between Relatives on the Supposition of Mendelian Inheritance |journal=[[Transactions of the Royal Society of Edinburgh]] |volume=52 |issue=2 |pages=399–433 |doi=10.1017/S0080456800012163 |s2cid=181213898 |oclc=4981124|url=https://zenodo.org/record/1428666 }} "Paper read by J. Arthur Thomson on July 8, 1918 to the Royal Society of Edinburgh."</ref> which showed how continuous variation could come from a number of discrete [[locus (genetics)|genetic loci]]. In this and other papers, culminating in his 1930 book ''[[The Genetical Theory of Natural Selection]]'',<ref>{{harvnb|Fisher|1999}}</ref> Fisher showed how Mendelian genetics was consistent with the idea of evolution by natural selection.<ref name="Larson221-243">{{harvnb|Larson|2004|pp=221–243}}</ref>{{efn|Fisher also analysed [[sexual selection]] in his book, but his work was largely ignored, and Darwin's case for such selection misunderstood, so it formed no substantial part of the modern synthesis.<ref>{{cite journal |last1=Hosken |first1=David J. |last2=House |first2=Clarissa M. |title=Sexual Selection |journal=[[Current Biology]] |date=25 January 2011 |volume=21 |issue=2 |pages=R62–R65 |doi=10.1016/j.cub.2010.11.053 |pmid=21256434|s2cid=18470445 |doi-access=free |bibcode=2011CBio...21..R62H }}</ref>}} In the 1920s, [[A Mathematical Theory of Natural and Artificial Selection|a series of papers]] by [[J. B. S. Haldane]] analyzed real-world examples of natural selection, such as the [[Peppered moth evolution|evolution of industrial melanism in peppered moths]].<ref name="Larson221-243" /> and showed that natural selection could work even faster than Fisher had assumed.<ref name="Bowler325-339">{{harvnb|Bowler|2003|pp=325–339}}</ref> Both of these scholars, and others, such as Dobzhansky and Wright, wanted to raise biology to the standards of the physical sciences by basing it on mathematical modeling and empirical testing. Natural selection, once considered unverifiable, was becoming predictable, measurable, and testable.<ref name=Smocovitis122>{{harvnb|Smocovitis|1996|pp=122–132}}</ref> ===De Beer's embryology, 1930=== The traditional view is that [[developmental biology]] played little part in the modern synthesis,<ref>{{harvnb|Smocovitis|1996|p=192}}</ref> but in his 1930 book ''[[Embryos and Ancestors]]'', the evolutionary embryologist [[Gavin de Beer]] anticipated [[evolutionary developmental biology]]<ref name="Held">{{cite book |last1=Held |first1=Lewis I. |author-link=Lewis I. Held |title=How the Snake Lost its Legs. Curious Tales from the Frontier of Evo-Devo |date=2014 |publisher=[[Cambridge University Press]] |isbn=978-1-107-62139-8 |page=67 |title-link=How the Snake Lost its Legs }}</ref> by showing that evolution could occur by [[heterochrony]],<ref>{{harvnb|Gould|1977|pp=221–222}}</ref> such as in [[paedomorphosis|the retention of juvenile features in the adult]].<ref>{{cite journal |last1=Hall |first1=B. K. |title=Evo-Devo: evolutionary developmental mechanisms |journal=[[International Journal of Developmental Biology]] |date=2003 |volume=47 |issue=7–8 |pages=491–495 |pmid=14756324 |citeseerx=10.1.1.113.5158 }}</ref> This, de Beer argued, could cause apparently sudden changes in the [[fossil record]], since embryos fossilise poorly. As the gaps in the fossil record had been used as an argument against Darwin's gradualist evolution, de Beer's explanation supported the Darwinian position.<ref>{{Cite journal |author=Ingo Brigandt |year=2006 |title=Homology and heterochrony: the evolutionary embryologist Gavin Rylands de Beer (1899-1972) |journal=[[Journal of Experimental Zoology]] |volume=306B |issue=4 |pages=317–328 |doi=10.1002/jez.b.21100 |url=https://www.ualberta.ca/~brigandt/de_Beer.pdf |archive-url=https://web.archive.org/web/20061104004810/http://www.ualberta.ca/~brigandt/de_Beer.pdf |archive-date=2006-11-04 |url-status=live |pmid=16506229|bibcode=2006JEZB..306..317B }}</ref> However, despite de Beer, the modern synthesis largely ignored embryonic development when explaining the form of organisms, since population genetics appeared to be an adequate explanation of how such forms evolved.<ref name=Gilbert1991>{{cite journal |last1=Gilbert |first1=Scott F. |author1-link=Scott F. Gilbert |author2=Opitz, J. M. |author3=Raff, R. A. |title=Resynthesizing evolutionary and developmental biology |journal=[[Developmental Biology (journal)|Developmental Biology]] |date=1996 |volume=173 |issue=2 |pages=357–372 |doi=10.1006/dbio.1996.0032|pmid=8605997|doi-access=free}}</ref><ref>{{cite book |last=Adams |first=M. |date=1991 |chapter=Through the looking glass: The evolution of Soviet Darwinism |title=New Perspectives in Evolution |editor1=Warren, L. |editor2=Koprowski, H. |publisher=Liss/Wiley |pages=[https://archive.org/details/newperspectiveso0000unse_u1t1/page/37 37–63] |isbn=978-0-471-56068-5 |chapter-url=https://archive.org/details/newperspectiveso0000unse_u1t1/page/37}}</ref>{{efn|Though [[C. H. Waddington]] had called for [[embryology]] to be added to the synthesis in his 1953 paper "Epigenetics and Evolution".<ref name=Smocovitis153/>}} ===Wright's adaptive landscape, 1932=== [[File:fitness-landscape-cartoon.png|thumb|[[Sewall Wright]] introduced the idea of a [[fitness landscape]] with local optima.]] {{further|Population genetics#History}} The population geneticist [[Sewall Wright]] focused on combinations of genes that interacted as complexes, and the effects of [[inbreeding]] on small relatively isolated populations, which could be subject to [[genetic drift]]. In a 1932 paper, he introduced the concept of an [[Fitness landscape|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.<ref name="Larson221-243" /><ref>{{harvnb|Wright|1932|pp=[http://www.esp.org/books/6th-congress/facsimile/contents/6th-cong-p356-wright.pdf 356–366]}}</ref> 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.<ref name="Bowler325-339" /> The work of Fisher, Haldane and Wright helped to found the discipline of theoretical population genetics.<ref name="auto1">{{cite journal |last1=Rose |first1=Michael R. |author-link1=Michael R. Rose |last2=Oakley |first2=Todd H. |date=November 24, 2007 |title=The new biology: beyond the Modern Synthesis |url=http://www.biologydirect.com/content/pdf/1745-6150-2-30.pdf |archive-url=https://web.archive.org/web/20140321054654/http://www.biologydirect.com/content/pdf/1745-6150-2-30.pdf |archive-date=2014-03-21 |url-status=live |journal=Biology Direct |volume=2 |issue=30 |pages=30 |doi=10.1186/1745-6150-2-30 |pmc=2222615 |pmid=18036242 |doi-access=free }}</ref><ref>{{cite book |author=Huxley, Julian |author-link=Julian Huxley |year=1942 |title=Evolution: The Modern Synthesis |url=https://archive.org/details/in.ernet.dli.2015.280031 |publisher=[[Allen & Unwin]]}}</ref><ref>{{cite book |author=Ridley, Matt |author-link=Matt Ridley |year=1996 |title=Evolution |edition=2nd |publisher=Blackwell Science |isbn=978-0632042920}}</ref> ===Dobzhansky's evolutionary genetics, 1937=== {{further|Genetics and the Origin of Species}} [[File:Drosophila pseudoobscura-Male.png|thumb|left|''[[Drosophila pseudoobscura]]'', the fruit fly which served as [[Theodosius Dobzhansky]]'s [[model organism]]]] [[Theodosius Dobzhansky]], an immigrant from the [[Soviet Union]] to the [[United States]], 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."<ref>{{harvnb|Mayr|Provine|1998|p=231}}</ref> Not surprisingly, there were other [[Russia]]n geneticists with similar ideas, though for some time their work was known to only a few in the [[Western world|West]]. His 1937 work ''[[Genetics and the Origin of Species]]''<ref>{{harvnb|Dobzhansky|1937}}</ref> 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.<ref name="Larson221-243"/><ref name="Bowler325-339"/> Further, Dobzhansky asserted the physicality, and hence the biological reality, of the mechanisms of inheritance: that evolution was based on material genes, arranged in a string on physical hereditary structures, the [[chromosome]]s, and [[genetic linkage|linked]] more or less strongly to each other according to their actual physical distances on the chromosomes. As with Haldane and Fisher, Dobzhansky's "evolutionary genetics"<ref>{{harvnb|Smocovitis|1996|p=127}}</ref> was a genuine science, now unifying cell biology, genetics, and both micro and macroevolution.<ref name=Smocovitis122/> His work 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 by driving change. He was influenced by his exposure in the 1920s to the work of [[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]].<ref name="Larson221-243"/><ref name="Bowler325-339"/> By 1937, Dobzhansky was able to argue that mutations were the main source of evolutionary changes and variability, along with chromosome rearrangements, effects of genes on their neighbours during development, and polyploidy. Next, genetic drift (he used the term in 1941), selection, migration, and geographical isolation could change gene frequencies. Thirdly, mechanisms like ecological or sexual isolation and hybrid sterility could fix the results of the earlier processes.<ref>{{cite book |last=Eldredge |first=Niles |title=Unfinished Synthesis: Biological Hierarchies and Modern Evolutionary Thought |url=https://books.google.com/books?id=fEYdRMjhPC4C&pg=PR9 |year=1985 |publisher=[[Oxford University Press]] |isbn=978-0-19-536513-9 |page=17}}</ref> ===Ford's ecological genetics, 1940=== [[File:Callimorpha.dominula.jpg|thumb|[[E. B. Ford]] studied [[Polymorphism (biology)#Scarlet tiger moth|polymorphism]] in the [[scarlet tiger moth]] for many years.]] {{further|Ecological genetics}} [[E. B. Ford]] was an experimental naturalist who wanted to test natural selection in nature, virtually inventing the field of [[ecological genetics]].<ref name=Ford1964>{{harvnb|Ford|1964}}</ref> 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. In 1940, he was the first to describe and define [[Polymorphism (biology)#Genetic polymorphism|genetic polymorphism]], and to predict that [[Human blood group systems|human blood group polymorphisms]] might be maintained in the population by providing some protection against disease.<ref name=Ford1964/><ref>{{harvnb|Ford|1975}}</ref> His 1949 book ''Mendelism and Evolution''<ref>{{cite book|last1=Ford|first1=E. B.|author-link1=E. B. Ford|title=Mendelism and Evolution |date=1949 |publisher=[[Methuen (publisher)|Methuen]]}}</ref> helped to persuade Dobzhansky to change the emphasis in the third edition of his famous textbook ''Genetics and the Origin of Species'' from drift to selection.<ref>{{harvnb|Dobzhansky|1951}}</ref> ===Schmalhausen's stabilizing selection, 1941=== {{further|Stabilizing selection}} [[Ivan Schmalhausen]] developed the theory of [[stabilizing selection]], the idea that selection can preserve a trait at some value, publishing a paper in Russian titled "Stabilizing selection and its place among factors of evolution" in 1941 and a monograph ''Factors of Evolution: The Theory of Stabilizing Selection''<ref>{{cite book |last1=Schmalhausen |first1=Ivan I. |last2=Dordick |first2=Isadore (trans.)|author-link1=Ivan Schmalhausen |editor1-last=Dobzhansky|editor1-first=Theodosius |editor1-link=Theodosius Dobzhansky |title=Factors of Evolution. The Theory of Stabilizing Selection |date=1949 |publisher=[[Blakiston Company]] |location=Philadelphia and Toronto}}</ref> in 1945. He developed it from J. M. Baldwin's 1902 concept that changes induced by the environment will ultimately be replaced by hereditary changes (including the [[Baldwin effect]] on behaviour), following that theory's implications to their Darwinian conclusion, and bringing him into conflict with Lysenkoism. Schmalhausen observed that stabilizing selection would remove most variations from the norm, most mutations being harmful.<ref name=Levit2006>{{cite journal | last=Levit | first=Georgy S. |author2=Hossfeld, Uwe |author3=Olsson, Lennart | title=From the 'Modern Synthesis' to Cybernetics: Ivan Ivanovich Schmalhausen (1884–1963) and his Research Program for a Synthesis of Evolutionary and Developmental Biology | journal=[[Journal of Experimental Zoology]] | volume=306B | issue=2006 | pages=89–106 | year=2006 | pmid=16419076 | doi=10.1002/jez.b.21087| s2cid=23594114 }}</ref><ref name=Adams1988>{{cite journal |author=Adams, M. B. |title=A Missing Link in the Evolutionary Synthesis. I. I. Schmalhausen. Factors of Evolution: The Theory of Stabilizing Selection |journal=Isis |date=June 1988 |volume=79 |issue=297 |pages=281–284 |doi=10.1086/354706 |pmid=3049441|s2cid=146660877 }}</ref><ref>{{cite journal |last1=Glass |first1=Bentley |title=Reviews and Brief Notices Factors of Evolution. The Theory of Stabilizing Selection. I. I. Schmalhausen, Isadore Dordick, Theodosius Dobzhansky |journal=[[Quarterly Review of Biology]] |date=December 1951 |volume=26 |issue=4 |pages=384–385 |doi=10.1086/398434}}</ref> Dobzhansky called the work "an important missing link in the modern view of evolution".{{sfn|Mayr|Provine|1998|p=ix}} ===Huxley's popularising synthesis, 1942=== {{main|Evolution: The Modern Synthesis}} [[File:Julian Huxley 1964.jpg|thumb|upright|[[Julian Huxley]] presented a serious but popularising version of the theory in his 1942 book ''[[Evolution: The Modern Synthesis]]''.]] In 1942, [[Julian Huxley]]'s serious but popularising<ref name=Ruse/><ref name=Lamm>{{cite web |last1=Lamm |first1=Ehud |title=Review of Julian Huxley, Evolution: The Modern Synthesis – The Definitive Edition, with a new foreword by Massimo Pigliucci and Gerd B. Müller |publisher=[[MIT Press]] |url=http://www.ehudlamm.com/huxley.pdf |archive-url=https://web.archive.org/web/20111224104526/http://www.ehudlamm.com/huxley.pdf |archive-date=2011-12-24 |url-status=live |access-date=21 August 2017}}</ref> ''[[Evolution: The Modern Synthesis]]''{{sfn|Huxley|2010}} introduced a name for the synthesis and intentionally set out to promote a "synthetic point of view" on the evolutionary process. He imagined a wide synthesis of many sciences: genetics, developmental physiology, ecology, systematics, palaeontology, cytology, and mathematical analysis of biology, and assumed that evolution would proceed differently in different groups of organisms according to how their genetic material was organised and their strategies for reproduction, leading to progressive but varying evolutionary trends.<ref name=Lamm/> His vision was of an "evolutionary humanism",<ref name=Smocovitis138/> with a system of ethics and a meaningful place for "Man" in the world grounded in a unified theory of evolution which would demonstrate progress leading to humanity at its summit. Natural selection was in his view a "fact of nature capable of verification by observation and experiment", while the "period of synthesis" of the 1920s and 1930s had formed a "more unified science",<ref name=Smocovitis138/> rivalling physics and enabling the "rebirth of Darwinism".<ref name=Smocovitis138>{{harvnb|Smocovitis|1996|pp=138–153}}</ref> However, the book was not the research text that it appeared to be. In the view of the philosopher of science [[Michael Ruse]], and in Huxley's own opinion, Huxley was "a generalist, a synthesizer of ideas, rather than a specialist".<ref name=Ruse>{{harvnb|Ruse|1996|pp=328–338}}</ref> Ruse observes that Huxley wrote as if he were adding empirical evidence to the mathematical framework established by Fisher and the population geneticists, but that this was not so. Huxley avoided mathematics, for instance not even mentioning [[Fisher's fundamental theorem of natural selection]]. Instead, Huxley used a mass of examples to demonstrate that natural selection is powerful and that it works on Mendelian genes. The book was successful in its goal of persuading readers of the reality of evolution, effectively illustrating topics such as [[island biogeography]], [[speciation]], and competition. Huxley further showed that the appearance of long-term [[orthogenesis|orthogenetic trends]] – predictable directions for evolution – in the fossil record were readily explained as [[allometry|allometric growth]] (since parts are interconnected). All the same, Huxley did not reject orthogenesis out of hand, but maintained a belief in progress all his life, with ''[[Homo sapiens]]'' as the endpoint, and he had since 1912 been influenced by the [[vitalism|vitalist]] philosopher [[Henri Bergson]], though in public he maintained an atheistic position on evolution.<ref name=Ruse/> Huxley's belief in progress within evolution and evolutionary humanism was shared in various forms by Dobzhansky, Mayr, Simpson and Stebbins, all of them writing about "the future of Mankind". Both Huxley and Dobzhansky admired the palaeontologist priest [[Pierre Teilhard de Chardin]], Huxley writing the introduction to Teilhard's 1955 book on orthogenesis, ''[[The Phenomenon of Man]]''. This vision required evolution to be seen as the central and guiding principle of biology.<ref name=Smocovitis138/> ===Mayr's allopatric speciation, 1942=== {{main|Systematics and the Origin of Species|Allopatric speciation}} [[File:Ernst Mayr PLoS.jpg|thumb|left|[[Ernst Mayr]] argued that [[allopatric speciation|geographic isolation]] was needed to provide sufficient [[reproductive isolation]] for [[speciation|new species to form]].]] [[Ernst Mayr]]'s key contribution to the synthesis was ''[[Systematics and the Origin of Species]]'', published in 1942.<ref>{{harvnb|Mayr|1999}}</ref> It asserted the importance of and set out to explain population variation in evolutionary processes including speciation. He analysed in particular the effects of [[Taxon|polytypic]] species, geographic variation, and isolation by geographic and other means.<ref>{{cite journal |last1=Hey |first1=Jody |last2=Fitch |first2=Walter M. |last3=Ayala |first3=Francisco J. |title=Systematics and the origin of species: An introduction |journal=[[PNAS]] |date=2005 |volume=102 |issue=supplement 1 |pages=6515–6519 |doi=10.1073/pnas.0501939102 |pmid=15851660|bibcode=2005PNAS..102.6515H |pmc=1131868 |doi-access=free }}</ref> 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 [[Species problem#Biological species concept|biological species concept]] that defined a species as a group of interbreeding or potentially interbreeding populations that were reproductively isolated from all other populations.<ref name="Larson221-243" /><ref name="Bowler325-339" /><ref>{{harvnb|Mayr|Provine|1998|pp=33–34}}</ref>{{sfn|Mayr|1982}} Before he left [[Germany]] for the United States in 1930, Mayr had been influenced by the work of the German biologist [[Bernhard Rensch]], who in the 1920s had analyzed the geographic distribution of polytypic species, paying particular attention to how variations between populations correlated with factors such as differences in climate.<ref>{{harvnb|Rensch|1947}}; {{harvnb|Rensch|1959}}</ref><ref>{{cite web |url=http://people.wku.edu/charles.smith/chronob/RENS1900.htm |title=Rensch, Bernhard (Carl Emmanuel) (Germany 1900-1990) |last=Smith |first=Charles H. |author-link=Charles H. Smith (historian of science) |work=Some Biogeographers, Evolutionists and Ecologists: Chrono-Biographical Sketches |publisher=[[Western Kentucky University]] |access-date=14 December 2017}}</ref><ref>{{harvnb|Mayr|Provine|1998|pp=298–299, 416}}</ref> [[File:Equine evolution.jpg|thumb|upright=1.2|[[George Gaylord Simpson]] argued against the naive view that [[evolution of the horse|evolution such as of the horse]] took place in a "straight-line". He noted that any chosen line is one path in a complex branching tree, [[natural selection]] having no [[orthogenesis|imposed direction]].]] ===Simpson's palaeontology, 1944=== [[George Gaylord Simpson]] was responsible for showing that the modern synthesis was compatible with palaeontology in his 1944 book ''[[Tempo and Mode in Evolution]]''. Simpson's work was crucial because so many palaeontologists 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 palaeontologists had used as support for [[Lamarckism#Neo-Lamarckism|neo-Lamarckism]] and orthogenesis did not hold up under careful examination. Instead, the [[fossil#Dating|fossil record]] was consistent with the irregular, branching, and non-directional pattern predicted by the modern synthesis.<ref name="Larson221-243" /><ref name="Bowler325-339" /> ===Society for the Study of Evolution, 1946=== During [[World War II]], Mayr edited a series of bulletins of the Committee on Common Problems of Genetics, Paleontology, and Systematics, formed in 1943, reporting on discussions of a "synthetic attack" on the interdisciplinary problems of evolution. In 1946, the committee became the Society for the Study of Evolution, with Mayr, Dobzhansky and Sewall Wright the first of the signatories. Mayr became the editor of its journal, ''[[Evolution (journal)|Evolution]]''. From Mayr and Dobzhansky's point of view, suggests the historian of science Betty Smocovitis, Darwinism was reborn, evolutionary biology was legitimised, and genetics and evolution were synthesised into a newly unified science. Everything fitted into the new framework, except "heretics" like [[Richard Goldschmidt]] who annoyed Mayr and Dobzhansky by insisting on the possibility of [[mutationism|speciation by macromutation]], creating "hopeful monsters". The result was "bitter controversy".<ref name=Smocovitis153>{{harvnb|Smocovitis|1996|pp=153–171}}</ref> [[File:Polyploidization.svg|thumb|[[Speciation]] via [[polyploidy]]: a [[diploid]] cell may fail to separate during [[meiosis]], producing diploid [[gamete]]s, which self-fertilize to produce a fertile tetraploid [[zygote]] that cannot interbreed with its parent species.]] ===Stebbins's botany, 1950=== The botanist [[G. Ledyard Stebbins]] extended the synthesis to encompass [[botany]]. He described the important effects on [[speciation]] of [[Hybridisation (biology)|hybridization]] and [[polyploidy]] in plants in his 1950 book ''[[Variation and Evolution in Plants]]''. These permitted evolution to proceed rapidly at times, polyploidy in particular evidently being able to create new species effectively instantaneously.<ref name="Larson221-243" /><ref name=Smocovitis2001>{{cite journal | last1=Smocovitis | first1=V. B. | year=2001 | title=G. Ledyard Stebbins and the evolutionary synthesis | journal=[[Annual Review of Genetics]] | volume=35 | pages=803–814 | doi=10.1146/annurev.genet.35.102401.091525 | pmid=11700300}}</ref> ==Definitions by the founders == The modern synthesis was defined differently by its various founders, with differing numbers of basic postulates, as shown in the table. {| class="wikitable" |+ Definitions of the modern synthesis by its founders, as they numbered them ! Component !! [[Ernst Mayr|Mayr]] 1959 !! [[G. Ledyard Stebbins|Stebbins]], 1966 !! [[Theodosius Dobzhansky|Dobzhansky]], 1974 |- | '''[[Mutation]]''' || (1) [[Random]]ness in all events that produce new genotypes, e.g. mutation <ref name=MayrEssence1959>Mayr, E.: Where Are We? Cold Spring Harbor Symposium of Quantitative Biology 24, 1–14, 1959</ref> || (1) a source of variability, but not of [[Orthogenesis|direction]]<ref name=Stebbins1966/> || (1) yields genetic raw materials<ref name=Dobzhansky1974>Dobzhansky, T.: In: Ayala, F., Dobzhansky, T. (eds.) Chance and Creativity in Evolution, pp. 307–338. [[University of California Press]], Berkeley and Los Angeles (1974)</ref> |- | '''[[genetic recombination|Recombination]]''' || (1) Randomness in recombination, [[fertilisation]]<ref name=MayrEssence1959/> || (2) a source of variability, but not of [[Orthogenesis|direction]]<ref name=Stebbins1966/> ||  |- | '''[[Chromosome|Chromosomal organisation]]''' ||  || (3) affects genetic linkage, arranges variation in [[gene pool]]<ref name=Stebbins1966/> ||  |- | '''[[Natural selection]]''' || (2) is only direction-giving factor,<ref name=MayrEssence1959/><ref name=MayrSynth1980>Mayr, E.: In: Mayr, E., Provine, W. (eds.) Some Thoughts on the History of the Evolutionary Synthesis, pp. 1–48. [[Harvard University Press]], 1980</ref> as seen in [[adaptation]]s to physical and biotic environment<ref name=MayrEssence1959/> || (4) guides changes to [[gene pool]]<ref name=Stebbins1966/> || (2) constructs evolutionary changes from genetic raw materials<ref name=Dobzhansky1974/> |- | '''[[Reproductive isolation]]''' ||  || (5) limits direction in which selection can guide the population<ref name=Stebbins1966>Stebbins, G. L.: Processes of Organic Evolution, p. 12. Prentice Hall, 1966</ref> || (3) makes divergence irreversible in [[sexual reproduction|sexual organisms]]<ref name=Dobzhansky1974/> |} ==After the synthesis== After the synthesis, evolutionary biology continued to develop with major contributions from workers including W. D. Hamilton,<ref name=Hamilton>{{cite journal |author=Hamilton, W. D. |date=1964 |title=The Genetical Evolution of Social Behaviour I |journal=[[Journal of Theoretical Biology]] |volume=7 |issue=1 |pages=1–52 |url=http://www.uvm.edu/pdodds/files/papers/others/1964/hamilton1964a.pdf |archive-url=https://web.archive.org/web/20161218171138/http://www.uvm.edu/pdodds/files/papers/others/1964/hamilton1964a.pdf |archive-date=2016-12-18 |url-status=live |doi=10.1016/0022-5193(64)90038-4|pmid=5875341 |bibcode=1964JThBi...7....1H }}</ref> George C. Williams,<ref name=Williams/> E. O. Wilson,<ref name=YudellDesalle2000/> Edward B. Lewis<ref name=Gilbert2000/> and others. ===Hamilton's inclusive fitness, 1964=== {{further|Inclusive fitness|Kin selection}} In 1964, [[W. D. Hamilton]] published two papers on "The Genetical Evolution of Social Behaviour". These defined [[inclusive fitness]] as the number of offspring equivalents an individual rears, rescues or otherwise supports through its behaviour. This was contrasted with personal reproductive fitness, the number of offspring that the individual directly begets. Hamilton, and others such as [[John Maynard Smith]], argued that a gene's success consisted in maximising the number of copies of itself, either by begetting them or by indirectly encouraging begetting by related individuals who shared the gene, the theory of [[kin selection]].<ref name=Hamilton/><ref>{{cite journal |last=Maynard Smith |first=John |author-link=John Maynard Smith |year=1964 |title=Group Selection and Kin Selection |journal=[[Nature (journal)|Nature]] |volume=201 |issue=4924 |pages=1145–1147 |doi=10.1038/2011145a0|bibcode=1964Natur.201.1145S |s2cid=4177102 }}</ref> ===Williams's gene-centred evolution, 1966=== {{further|Gene-centered view of evolution|Adaptation and Natural Selection}} In 1966, [[George C. Williams (biologist)|George C. Williams]] published ''[[Adaptation and Natural Selection]]'', outlined a [[gene-centered view of evolution|gene-centred view of evolution]] following Hamilton's concepts, disputing the idea of [[evolutionary progress]], and attacking the then widespread theory of [[group selection]]. Williams argued that natural selection worked by changing the frequency of alleles, and could not work at the level of groups.<ref>{{cite book |last=Pinker |first=Steven |author-link=Steven Pinker |year=1994 |title=The Language Instinct |publisher=Harper Perennial Modern Classics |page=294}}</ref><ref name=Williams>{{cite book |last=Williams |first=George C. |title=Adaptation and Natural Selection |publisher=[[Princeton University Press]] |year=1966 |pages=307 |url=http://www.librarything.com/work/192870 |isbn=978-0-691-02615-2}}</ref> Gene-centred evolution was popularised by [[Richard Dawkins]] in his 1976 book ''[[The Selfish Gene]]'' and developed in his more technical writings.<ref>{{cite web |url=https://plato.stanford.edu/archives/fall2015/entries/population-genetics/ |title=Population Genetics |first=Samir |last=Okasha |date=September 22, 2006 |via=plato.stanford.edu}}</ref><ref name="extendedphenotype">{{cite book |last=Dawkins| first=Richard |author-link=Richard Dawkins |year=1982 |title=The Extended Phenotype |publisher=[[Oxford University Press]] |isbn=978-0-19-288051-2 |title-link=The Extended Phenotype}}</ref> ===Wilson's sociobiology, 1975=== [[File:Atta.cephalotes.gamut.selection.jpg|thumb|[[Ant]] [[sociobiology|societies have evolved]] elaborate [[caste (biology)|caste]] structures, widely different in size and function.]] {{main|Sociobiology}} In 1975, [[E. O. Wilson]] published his controversial<ref name=Fisher1994>{{cite web |last=Fisher |first=Helen |title='Wilson,' They Said, 'Your All Wet!' |url=https://www.nytimes.com/books/98/12/06/specials/wilson-naturalist.html |work=New York Times |access-date=21 July 2015 |date=16 October 1994}}</ref> book ''[[Sociobiology: The New Synthesis]]'', the subtitle alluding to the modern synthesis<ref name=YudellDesalle2000>{{cite journal |last1=Yudell |first1=Michael |last2=Desalle |first2=Rob |year=2000 |title=Sociobiology. The New Synthesis. by Edward O. Wilson |journal=[[Journal of the History of Biology]] |volume=33 |issue=3 |pages=577–584 |jstor=4331614 |doi=10.1023/a:1004845822189 |s2cid=88047081 }}</ref> as he attempted to bring the study of animal society into the evolutionary fold. This appeared radically new, although Wilson was following Darwin, Fisher, Dawkins and others.<ref name=YudellDesalle2000/> Critics such as [[Gerhard Lenski]] noted that he was following Huxley, Simpson and Dobzhansky's approach, which Lenski considered needlessly reductive as far as human society was concerned.<ref name=Lenski1976>{{cite journal| last=Lenski |first=Gerhard |year=1976 |title=Sociobiology. The New Synthesis. by Edward O. Wilson |journal=[[Social Forces]] |volume=55 |issue=2 |pages=530–531 |jstor=2576242 |doi=10.2307/2576242}}</ref> By 2000, the proposed discipline of [[sociobiology]] had morphed into the relatively well-accepted discipline of [[evolutionary psychology]].<ref name=YudellDesalle2000/> ===Lewis's homeotic genes, 1978=== [[File:Genes hox.jpeg|thumb|[[Evolutionary developmental biology]] has formed a synthesis of evolutionary and [[developmental biology]], discovering [[deep homology]] between the [[embryogenesis]] of such different animals as [[insect]]s and [[vertebrate]]s.]] {{main|Evolutionary developmental biology}} In 1977, [[recombinant DNA]] technology enabled biologists to start to explore the genetic control of development. The growth of [[evolutionary developmental biology]] from 1978, when [[Edward B. Lewis]] discovered [[homeotic]] genes, showed that many so-called [[toolkit gene]]s act to regulate development, influencing the expression of other genes. It also revealed that some of the regulatory genes are extremely ancient, so that animals as different as insects and mammals share control mechanisms; for example, the ''[[Pax6]]'' gene is involved in forming the [[eye]]s of mice and of fruit flies. Such [[deep homology]] provided strong evidence for evolution and indicated the paths that evolution had taken.<ref name=Gilbert2000>{{cite book |last=Gilbert |first=Scott F. |author-link=Scott F. Gilbert |chapter=A New Evolutionary Synthesis |title=Developmental Biology |date=2000 |publisher=[[Sinauer Associates]] |url=https://www.ncbi.nlm.nih.gov/books/NBK10128/}}</ref> ==Later syntheses== In 1982, a historical note on a series of evolutionary biology books{{efn|In a reissue of Dobzhansky's ''Genetics and the Origin of Species''.}} could state without qualification that evolution is the central organizing principle of biology. Smocovitis commented on this that "What the architects of the synthesis had worked to construct had by 1982 become a matter of fact", adding in a footnote that "the centrality of evolution had thus been rendered [[tacit knowledge]], part of the [[received wisdom]] of the profession".{{sfn|Smocovitis|1996|pp=186–187}} By the late 20th century, however, the modern synthesis was showing its age, and fresh syntheses to remedy its defects and fill in its gaps were proposed from different directions. These have included such diverse fields as the [[sociology|study of society]],<ref name=YudellDesalle2000/> developmental biology,<ref name=Gilbert1991/> epigenetics,<ref name=pigliucci/> [[molecular biology]], [[microbiology]], [[genomics]],<ref name=Koonin2009>{{cite journal |last1=Koonin |first1=Eugene V. |author-link=Eugene Koonin |title=The Origin at 150: is a new evolutionary synthesis in sight? |journal=[[Trends in Genetics]] |date=November 2009 |volume=25 |issue=11 |pages=473–475 |doi=10.1016/j.tig.2009.09.007 |pmid=19836100 |pmc=2784144 }}</ref> [[symbiogenesis]], and [[horizontal gene transfer]].<ref name=Noble2011/> The physiologist [[Denis Noble]] argues that these additions render neo-Darwinism in the sense of the early 20th century's modern synthesis "at the least, incomplete as a theory of evolution",<ref name=Noble2011>{{cite journal |last1=Noble |first1=Denis |title=Neo-Darwinism, the Modern Synthesis and selfish genes: are they of use in physiology? |journal=[[The Journal of Physiology]] |volume=589 |issue=5 |year=2011 |pages=1007–1015 |doi=10.1113/jphysiol.2010.201384 |pmid=21135048 |pmc=3060581 }}</ref> and one that has been falsified by later biological research.<ref name=Noble2011/> Michael Rose and Todd Oakley note that evolutionary biology, formerly divided and "[[Balkanization|Balkanized]]", has been brought together by genomics. It has in their view discarded at least five common assumptions from the modern synthesis, namely that the genome is always a well-organised set of genes; that each gene has a single function; that species are well adapted biochemically to their ecological niches; that species are the durable units of evolution, and all levels from organism to organ, cell and molecule within the species are characteristic of it; and that the design of every organism and cell is efficient. They argue that the "new biology" integrates genomics, [[bioinformatics]], and evolutionary genetics into a general-purpose toolkit for a "Postmodern Synthesis".<ref name="auto1"/> ===Pigliucci's extended evolutionary synthesis, 2007=== {{main|Extended evolutionary synthesis}} In 2007, more than half a century after the modern synthesis, [[Massimo Pigliucci]] called for an [[extended evolutionary synthesis]] to incorporate aspects of biology that had not been included or had not existed in the mid-20th century.<ref>{{cite journal | last=Wade | first=Michael J. | year=2011 | title=The Neo-Modern Synthesis: The Confluence of New Data and Explanatory Concepts | journal=[[BioScience]] | volume=61 | issue=5| pages=407–408 | doi=10.1525/bio.2011.61.5.10| doi-access=free }}</ref><ref name="Smee 2015">John Odling-Smee ''et al''. [http://rspb.royalsocietypublishing.org/content/282/1813/20151019 "The extended evolutionary synthesis: its structure, assumptions and predictions"]. Proceedings of the Royal Society B: Biological Sciences, August 2015.</ref> It revisits the relative importance of different factors, challenges assumptions made in the modern synthesis, and adds new factors<ref name="Smee 2015"/><ref>{{cite journal | last1=Wade | first1=Michael J. | year=2011 | title=The Neo-Modern Synthesis: The Confluence of New Data and Explanatory Concepts | journal=BioScience | volume=61 | issue=5 | pages=407–408 | doi=10.1525/bio.2011.61.5.10| doi-access=free }}</ref> such as [[Group selection#Multilevel selection theory|multilevel selection]], [[transgenerational epigenetic inheritance]], [[niche construction]], and [[evolvability]].<ref name=beyonddna>{{cite journal | last1=Danchin | first1=É. | last2=Charmantier | first2=A. | last3=Champagne | first3=F. A. | last4=Mesoudi | first4=A. | last5=Pujol | first5=B. | last6=Blanchet | first6=S. | year=2011 | title=Beyond DNA: integrating inclusive inheritance into an extended theory of evolution | journal=[[Nature Reviews Genetics]] | volume=12 | issue=7| pages=475–486 | doi=10.1038/nrg3028 | pmid=21681209| s2cid=8837202 }}</ref><ref name=pigliucci>{{cite journal | last1=Pigliucci | first1=Massimo | last2=Finkelman | first2=Leonard | year=2014 | title=The Extended (Evolutionary) Synthesis Debate: Where Science Meets Philosophy | journal=BioScience | volume=64 | issue=6| pages=511–516 | doi=10.1093/biosci/biu062| doi-access=free }}</ref><ref name="Laubichler 2015">{{cite journal | last1=Laubichler | first1=Manfred D. | last2=Renn | first2=Jürgen | year=2015 | title=Extended evolution: A Conceptual Framework for Integrating Regulatory Networks and Niche Construction | journal=Journal of Experimental Zoology Part B: Molecular and Developmental Evolution | volume=324 | issue=7 | pages=565–577 | doi=10.1002/jez.b.22631| pmid=26097188 | pmc=4744698 | bibcode=2015JEZB..324..565L }}</ref> ===Koonin's 'post-modern' evolutionary synthesis, 2009=== [[File:Tree Of Life (with horizontal gene transfer).svg|thumb|A 21st century [[Tree of life (biology)|tree of life]] showing [[horizontal gene transfer]]s among [[prokaryote]]s and the saltational [[endosymbiosis]] events that created the [[eukaryote]]s, neither fitting into the 20th century's modern synthesis]] In 2009, Darwin's 200th anniversary, the ''Origin of Species''{{'}} 150th, and the 200th of Lamarck's "early evolutionary synthesis",<ref name=Koonin2009/> ''[[Philosophie Zoologique]]'', the evolutionary biologist [[Eugene Koonin]] stated that while "the edifice of the [early 20th century] Modern Synthesis has crumbled, apparently, beyond repair",<ref name=Koonin2009/> a new 21st-century synthesis could be glimpsed. Three interlocking revolutions had, he argued, taken place in evolutionary biology: molecular, microbiological, and genomic. The [[molecular biology|molecular revolution]] included the [[Neutral theory of molecular evolution|neutral theory]], that most mutations are neutral and that [[Negative selection (natural selection)|negative selection]] happens more often than the [[Directional selection|positive]] form, and that all current life evolved from [[Last Universal Common Ancestor|a single common ancestor]]. In microbiology, the synthesis has expanded to cover the [[prokaryote]]s, using [[ribosomal RNA]] to form a [[tree of life (biology)|tree of life]]. Finally, [[genomics]] brought together the molecular and microbiological syntheses - in particular, [[horizontal gene transfer]] between [[bacteria]] shows that prokaryotes can freely share genes. Many of these points had already been made by other researchers such as Ulrich Kutschera and [[Karl J. Niklas]].<ref name="Kutschera Niklas 2004">{{cite journal |last1=Kutschera |first1=Ulrich |author-link1=Ulrich Kutschera |last2=Niklas |first2=Karl J. |author-link2=Karl J. Niklas |date=June 2004 |title=The modern theory of biological evolution: an expanded synthesis |journal=[[Naturwissenschaften]] |volume=91 |issue=6 |pages=255–276 |bibcode=2004NW.....91..255K |doi=10.1007/s00114-004-0515-y |pmid=15241603 |s2cid=10731711 }}</ref> ===Towards a replacement synthesis=== [[File:Modern Synthesis Limits.svg|thumb|upright=2.2|Inputs to the modern synthesis, with other topics (inverted colours) such as developmental biology that were not joined with evolutionary biology until the turn of the 21st century<ref name="Kutschera Niklas 2004"/>]] Biologists, alongside scholars of the history and philosophy of biology, have continued to debate the need for, and possible nature of, a replacement synthesis. For example, in 2017 Philippe Huneman and Denis M. Walsh stated in their book ''Challenging the Modern Synthesis'' that numerous theorists had pointed out that the disciplines of embryological developmental theory, morphology, and ecology had been omitted. They noted that all such arguments amounted to a continuing desire to replace the modern synthesis with one that united "all biological fields of research related to evolution, adaptation, and diversity in a single theoretical framework."<ref>{{cite book |last1=Huneman |first1=Philippe |last2=Walsh |first2=Denis M. |title=Challenging the Modern Synthesis: Adaptation, Development, and Inheritance |url=https://books.google.com/books?id=72EwDwAAQBAJ&pg=PT76 |year=2017 |publisher=[[Oxford University Press]] |isbn=978-0-19-068145-6 |pages=76 (Chapter 2)}}</ref> They observed further that there are two groups of challenges to the way the modern synthesis viewed inheritance. The first is that other modes such as [[epigenetic inheritance]], [[phenotypic plasticity]], the [[Baldwin effect]], and the [[maternal effect]] allow new characteristics to arise and be passed on and for the genes to catch up with the new adaptations later. The second is that all such mechanisms are part, not of an inheritance system, but a [[Developmental systems theory|developmental system]]: the fundamental unit is not a discrete selfishly competing gene, but a collaborating system that works at all levels from genes and cells to organisms and cultures to guide evolution.<ref>{{cite book |last1=Huneman |first1=Philippe |last2=Walsh |first2=Denis M. |title=Challenging the Modern Synthesis: Adaptation, Development, and Inheritance |year=2017 |publisher=[[Oxford University Press]] |isbn=978-0-19-068145-6 |pages=Introduction}}</ref> The molecular biologist [[Sean B. Carroll]] has commented that had Huxley had access to [[evolutionary developmental biology]], "embryology would have been a cornerstone of his Modern Synthesis, and so evo-devo is today a key element of a more complete, expanded evolutionary synthesis."<ref name=Carroll_2008>{{cite journal |last1=Carroll |first1=Sean B. |author1-link=Sean B. Carroll |title=Evo-Devo and an Expanding Evolutionary Synthesis: A Genetic Theory of Morphological Evolution |journal=Cell |date=2008 |volume=134 |issue=1 |pages=25–36|doi=10.1016/j.cell.2008.06.030 |pmid=18614008|s2cid=2513041 |doi-access=free }}</ref>  == Historiography == Looking back at the conflicting accounts of the modern synthesis, the historian Betty Smocovitis notes in her 1996 book ''Unifying Biology: The Evolutionary Synthesis and Evolutionary Biology'' that both historians and philosophers of biology have attempted to grasp its scientific meaning, but have found it "a moving target";<ref name=Smocovitis187>{{harvnb|Smocovitis|1996|p=187}}</ref> the only thing they agreed on was that it was a historical event.<ref name=Smocovitis187/> In her words<blockquote>"by the late 1980s the notoriety of the evolutionary synthesis was recognized ... So notorious did 'the synthesis' become, that few serious historically minded analysts would touch the subject, let alone know where to begin to sort through the interpretive mess left behind by the numerous critics and commentators".<ref>{{harvnb|Smocovitis|1996|p=43}}</ref></blockquote> == See also == * [[Objections to evolution]] ==Notes== {{notelist}} ==References== {{Reflist}} ==Sources== * {{cite book |last=Bateson |first=William |author-link=William Bateson |year=1894 |title=Materials for the Study of Variation Treated with Especial Regard to Discontinuity in the Origin of Species |url=https://archive.org/details/materialsforstud00bate |location=London; New York |publisher=[[Macmillan Publishers|Macmillan]] |lccn=07001821 |oclc=1944285}} * {{cite book |last=Bowler |first=Peter J. |author-link=Peter J. Bowler |year=2003 |title=Evolution: The History of an Idea |edition=3rd completely rev. and expanded |location=Berkeley, CA |publisher=[[University of California Press]] |isbn=978-0-520-23693-6 |url-access=registration |url=https://archive.org/details/evolutionhistory0000bowl_n7y8}} ** {{cite book |last=Bowler |first=Peter J. |author-link=Peter J. Bowler |year=1989 |title=Evolution: The History of an Idea |edition=2nd revised |location=Berkeley, CA |publisher=[[University of California Press]] |isbn=978-0-520-06386-0 |url-access=registration |url=https://archive.org/details/evolutionhistory0000bowl}} * {{cite book |last=Dobzhansky |first=Theodosius |author-link=Theodosius Dobzhansky |year=1937 |title=Genetics and the Origin of Species |series=[[Columbia University Biological Series]] |location=New York |publisher=[[Columbia University Press]] |lccn=37033383 |oclc=766405|title-link=Genetics and the Origin of Species}} ** {{cite book |last=Dobzhansky |first=Theodosius |year=1951 |title=Genetics and the Origin of Species |url=https://archive.org/details/in.ernet.dli.2015.547790 |series=Columbia University Biological Series |edition=3rd revised |location=New York |publisher=Columbia University Press |lccn=51014816 |oclc=295774 |author-mask=2}} * {{cite book |last=Fisher |first=R. A. |author-link=Ronald Fisher |year=1999 |orig-year=1930 |title=The Genetical Theory of Natural Selection |others=Edited with a foreword and notes by J. H. Bennett |edition=A complete variorum |location=Oxford, UK |publisher=Oxford University Press |isbn=978-0-19-850440-5 |title-link=The Genetical Theory of Natural Selection}} * {{cite journal |last=Ford |first=E. B. |author-link=E. B. Ford |year=1964 |title=Ecological Genetics |journal=Advancement of Science |volume=25 |issue=124 |pages=227–35 |location=London; New York |publisher=[[Methuen Publishing]]; [[John Wiley & Sons]] |pmid=5701915 |lccn=64009038 |oclc=875507052}} ** {{cite journal |last=Ford |first=E. B. |year=1975 |title=Ecological Genetics |journal=Advancement of Science |volume=25 |issue=124 |pages=227–35 |edition=4th |location=London; New York |publisher=[[Chapman & Hall|Chapman and Hall]]; John Wiley & Sons |pmid=5701915 |lccn=75002165 |oclc=1890603 |author-mask=2}} * {{cite book |last=Gould |first=Stephen Jay |author-link=Stephen Jay Gould |year=1977 |title=Ontogeny and Phylogeny |publisher=[[Harvard University Press|Belknap Press of Harvard University Press]] |isbn=978-0-674-63940-9 |title-link=Ontogeny and Phylogeny (book)}} * {{cite book |last=Gould |first=Stephen Jay |year=2002 |title=The Structure of Evolutionary Theory |publisher=Belknap Press of Harvard University Press |isbn=978-0-674-00613-3 |title-link=The Structure of Evolutionary Theory}} * {{cite book |editor1-last=Grafen |editor1-first=Alan |editor1-link=Alan Grafen |editor2-last=Ridley |editor2-first=Mark |editor2-link=Mark Ridley (zoologist) |year=2006 |title=Richard Dawkins: How a Scientist Changed the Way We Think |publisher=Oxford University Press |isbn=978-0-19-929116-8 |title-link=Richard Dawkins: How a Scientist Changed the Way We Think}} * {{cite book |last=Huxley |first=Julian |author-link=Julian Huxley |year=2010 |orig-year=1942 |others=With a new foreword by [[Massimo Pigliucci]] and [[Gerd Müller (theoretical biologist)|Gerd B. Müller]] |edition=Definitive |title=Evolution: The Modern Synthesis |location=Cambridge, MA |publisher=[[MIT Press]] |isbn=978-0-262-51366-1 |title-link=Evolution: The Modern Synthesis}} * {{cite book |last=Larson |first=Edward J. |author-link=Edward J. Larson |year=2004 |title=Evolution: The Remarkable History of a Scientific Theory |series=Modern Library Chronicles |volume=17 |location=New York |publisher=[[Modern Library]] |isbn=978-0-679-64288-6 |url=https://archive.org/details/evolutionremarka00lars}} * {{cite book |last=Mayr |first=Ernst |author-link=Ernst Mayr |year=1982 |title=The Growth of Biological Thought: Diversity, Evolution, and Inheritance |location=Cambridge, MA |publisher=Belknap Press of Harvard University Press |isbn=978-0-674-36445-5 |url=https://archive.org/details/growthofbiologic00mayr}} * {{cite book |last=Mayr |first=Ernst |year=1999 |orig-year=1942 |title=Systematics and the Origin of Species from the Viewpoint of a Zoologist |edition=1st Harvard University Press pbk. |publisher=[[Harvard University Press]] |isbn=978-0-674-86250-0 |title-link=Systematics and the Origin of Species}} * {{cite book |editor-last1=Mayr |editor1-first=Ernst |editor2-last=Provine |editor2-first=William B. |editor2-link=Will Provine |year=1998 |orig-year=1980 |title=The Evolutionary Synthesis: Perspectives on the Unification of Biology |others=With a new preface by Ernst Mayr |edition=1st paperback |location=Cambridge, MA |publisher=Harvard University Press |isbn=978-0-674-27226-2}} * {{cite book |last=Provine |first=W. B. |year=2001 |title=The Origins of Theoretical Population Genetics, with a new afterword |publisher=University of Chicago Press |isbn=978-0-226-68464-2}} * {{cite book |last=Rensch |first=Bernhard |author-link=Bernhard Rensch |year=1947 |title=Neuere Probleme der Abstammungslehre. Die transspezifische Evolution |trans-title=Newer Problems of Evolutionary Theory: The trans-specific Evolution |language=de |location=Stuttgart |publisher=Ferdinand Enke Verlag |oclc=2271422}} ** {{cite journal |last=Rensch |first=Bernhard |year=1959 |title=Evolution Above the Species Level |journal=American Journal of Physical Anthropology |type=English translation of 2nd edition of ''Neuere Probleme der Abstammungslehre'' (1954) |series=Columbia Biological Series |volume=19 |issue=3 |pages=408–410 |doi=10.1002/ajpa.1330200329 |lccn=60002460 |oclc=3677530 |author-mask=2}} * {{cite book |last=Ruse |first=Michael |author-link=Michael Ruse |year=1996 |title=Monad to Man: the Concept of Progress in Evolutionary Biology |url=https://archive.org/details/monadtomanconcep0000ruse |url-access=registration |publisher=Harvard University Press |isbn=978-0-674-03248-4}} * {{cite journal |last=Smocovitis |first=Vassiliki Betty |year=1996 |title=Unifying Biology: The Evolutionary Synthesis and Evolutionary Biology |journal=Journal of the History of Biology |volume=25 |issue=1 |pages=1–65 |location=Princeton, NJ |publisher=Princeton University Press |doi=10.1007/bf01947504 |pmid=11623198 |isbn=978-0-691-03343-3 |s2cid=189833728}} * {{cite book |last=Wright |first=Sewall |author-link=Sewall Wright |year=1932 |chapter=The Roles of Mutation, Inbreeding, Crossbreeding and Selection in Evolution |editor-last=Jones |editor-first=Donald F. |editor-link=Donald F. Jones |title=Proceedings of the Sixth International Congress of Genetics |volume=1 |location=Ithaca, NY |publisher=[[Genetics Society of America]] |oclc=439596433}} ==Further reading== * {{cite book |last=Allen |first=Garland E. |author-link=Garland E. Allen |year=1978 |title=Thomas Hunt Morgan: The Man and His Science |location=Princeton, NJ |publisher=[[Princeton University Press]] |isbn=978-0-691-08200-4 |ref=none}} * {{cite book |last=Dawkins |first=Richard |author-link=Richard Dawkins |year=1990 |title=The Blind Watchmaker |series=Penguin Science |location=London |publisher=[[Penguin Books]] |isbn=978-0-14-014481-9|title-link=The Blind Watchmaker |ref=none}} * {{cite book |last=Futuyma |first=Douglas J. |author-link=Douglas J. Futuyma |year=1998 |title=Evolutionary Biology |edition=3rd |location=Sunderland, MA |publisher=[[Sinauer Associates]] |isbn=978-0-87893-189-7 |ref=none}} * {{cite book |last=Haldane |first=J. B. S. |author-link=J. B. S. Haldane |year=1932 |title=The Causes of Evolution |location=London; New York |publisher=[[Longman|Longmans, Green & Co.]] |lccn=32033284 |oclc=5006266|title-link=The Causes of Evolution |ref=none}} "This book is based on a series of lectures delivered in January 1931 at the Prifysgol Cymru, Aberystwyth, and entitled 'A re-examination of Darwinism'." * {{cite book |editor-last=Huxley |editor-first=Julian |editor-link=Julian S. Huxley |year=1976 |orig-year=Originally published 1940; Oxford, UK: [[Oxford University Press#Clarendon Press|The Clarendon Press]] |title=The New Systematics |edition=Reprint |location=St. Clair Shores, MI |publisher=Scholarly Press |isbn=978-0-403-01786-7 |ref=none}} * {{Cite book |title=Rethinking evolution: the revolution that's hiding in plain sight |last=Levinson |first=Gene |publisher=World Scientific |year=2020 |isbn=9781786347268 |url=https://rethinkingevolution.com/ |ref=none |access-date=2020-01-27 |archive-date=2022-05-21 |archive-url=https://web.archive.org/web/20220521082753/https://rethinkingevolution.com/ |url-status=dead }} * {{cite journal |last=Wright |first=Sewall |author-link=Sewall Wright |date=March 1, 1931 |title=Evolution in Mendelian Populations |journal=[[Genetics (journal)|Genetics]] |volume=16 |issue=2 |pages=97–159 |doi=10.1093/genetics/16.2.97 |pmid=17246615 |pmc=1201091 |ref=none}} {{evolution}} {{Evolutionary psychology}} {{Authority control}} 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