Editing Genetic drift (section)

==History==
{{further|Modern synthesis (20th century)}}
The role of random chance in evolution was first outlined by Arend L. Hagedoorn and Anna Cornelia Hagedoorn-Vorstheuvel La Brand in 1921.<ref>{{cite book |vauthors=Hagedoorn AL, Hagedoorn-Vorstheuvel La Brand AC |date=1921 |title=The Relative Value of the Processes Causing Evolution |url=https://www.biodiversitylibrary.org/item/116829#page/9/mode/1up |location=The Hague |publisher=Martinus Nijhoff |page=<!-- or pages= --> |access-date=28 March 2019 |archive-date=28 March 2019 |archive-url=https://web.archive.org/web/20190328165042/https://www.biodiversitylibrary.org/item/116829#page/9/mode/1up |url-status=live }}</ref> They highlighted that random survival plays a key role in the loss of variation from populations. Fisher (1922) responded to this with the first, albeit marginally incorrect, mathematical treatment of the "Hagedoorn effect".<ref>{{cite journal | vauthors = Fisher RA | date = 1922 | title = On the Dominance Ratio | journal = Proceedings of the Royal Society of Edinburgh | volume = 42 | pages = 321–341 | doi = 10.1017/s0370164600023993 }}</ref> Notably, he expected that many natural populations were too large (an N ~10,000) for the effects of drift to be substantial and thought drift would have an insignificant effect on the evolutionary process. The corrected mathematical treatment and term "genetic drift" was later coined by a founder of [[population genetics]], [[Sewall Wright]]. His first use of the term "drift" was in 1929,<ref>{{cite journal | vauthors = Wright S |author-link=Sewall Wright |date=November–December 1929 |title=The evolution of dominance |journal=The American Naturalist |location=Chicago, IL |publisher=University of Chicago Press on behalf of the American Society of Naturalists |volume=63 |issue=689 |pages=556–561 |doi=10.1086/280290 |issn=0003-0147 |jstor=2456825|bibcode=1929ANat...63..556W |s2cid=85301374 }}</ref> though at the time he was using it in the sense of a directed process of change, or natural selection. Random drift by means of sampling error came to be known as the "Sewall–Wright effect", though he was never entirely comfortable to see his name given to it. Wright referred to all changes in allele frequency as either "steady drift" (e.g., selection) or "random drift" (e.g., sampling error).<ref name="Wright55">{{cite journal | vauthors = Wright S | title = Classification of the factors of evolution | journal = Cold Spring Harbor Symposia on Quantitative Biology | volume = 20 | pages = 16–24D | year = 1955 | pmid = 13433551 | doi = 10.1101/SQB.1955.020.01.004 | publisher = Cold Spring Harbor Laboratory Press | name-list-style = vanc }} Symposium: "Population Genetics: The Nature and Causes of Genetic Variability in Populations".</ref> "Drift" came to be adopted as a technical term in the [[stochastic]] sense exclusively.<ref>{{harvnb|Stevenson|1991}}</ref> Today it is usually defined still more narrowly, in terms of sampling error,<ref>{{harvnb|Freeman|Herron|2007}}</ref> although this narrow definition is not universal.<ref>{{cite journal | vauthors = Masel J | title = Rethinking Hardy-Weinberg and genetic drift in undergraduate biology | journal = BioEssays | volume = 34 | issue = 8 | pages = 701–710 | date = August 2012 | pmid = 22576789 | doi = 10.1002/bies.201100178 | publisher = John Wiley & Sons | s2cid = 28513167 }}</ref><ref>{{harvnb|Lynch|2007}}</ref> Wright wrote that the "restriction of "random drift" or even "drift" to only one component, the effects of accidents of sampling, tends to lead to confusion".<ref name="Wright55" /> Sewall Wright considered the process of random genetic drift by means of sampling error equivalent to that by means of inbreeding, but later work has shown them to be distinct.<ref>{{cite journal | vauthors = Crow JF | title = Wright and Fisher on inbreeding and random drift | journal = Genetics | volume = 184 | issue = 3 | pages = 609–611 | date = March 2010 | pmid = 20332416 | pmc = 2845331 | doi = 10.1534/genetics.109.110023 | publisher = Genetics Society of America | author-link = James F. Crow }}</ref>

In the early days of the [[Modern synthesis (20th century)|modern evolutionary synthesis]], scientists were beginning to blend the new science of population genetics with [[Charles Darwin]]'s theory of natural selection. Within this framework, Wright focused on the effects of inbreeding on small relatively isolated populations. 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 in turn allow natural selection to push them towards new adaptive peaks.<ref name="Larson221-243">{{harvnb|Larson|2004|pp=221–243}}</ref> Wright thought smaller populations were more suited for natural selection because "inbreeding was sufficiently intense to create new interaction systems through random drift but not intense enough to cause random nonadaptive fixation of genes".<ref>{{harvnb|Stevenson|1991}}: Quote attributed to [[Will Provine|William B. Provine]] in ''The Origins of Theoretical Population Genetics'' (1971), p. 162; Chicago: University of Chicago Press.</ref>

Wright's views on the role of genetic drift in the evolutionary scheme were controversial almost from the very beginning. One of the most vociferous and influential critics was colleague Ronald Fisher. Fisher conceded genetic drift played some role in evolution, but an insignificant one. Fisher has been accused of misunderstanding Wright's views because in his criticisms Fisher seemed to argue Wright had rejected selection almost entirely. To Fisher, viewing the process of evolution as a long, steady, adaptive progression was the only way to explain the ever-increasing complexity from simpler forms. But the debates have continued between the "gradualists" and those who lean more toward the Wright model of evolution where selection and drift together play an important role.<ref>{{harvnb|Avers|1989}}</ref>

In 1968, [[Motoo Kimura]] rekindled the debate with his neutral theory of [[molecular evolution]], which claims that most of the genetic changes are caused by genetic drift acting on neutral mutations.<ref name="Kimura_1968" /><ref name="Futuyma 1998 320" />

The role of genetic drift by means of sampling error in evolution has been criticized by [[John H. Gillespie]]<ref>{{cite journal | vauthors = Gillespie JH | title = Genetic drift in an infinite population. The pseudohitchhiking model | journal = Genetics | volume = 155 | issue = 2 | pages = 909–919 | date = June 2000 | pmid = 10835409 | pmc = 1461093 | doi = 10.1093/genetics/155.2.909 | publisher = Genetics Society of America }}</ref> and [[Will Provine|William B. Provine]], who argue that selection on linked sites is a more important stochastic force.