Editing Natural selection (section)

===Darwin's theory===

{{Main|Inception of Darwin's theory|Development of Darwin's theory}}
{{Further|Coloration evidence for natural selection}}

[[File:Charles Darwin seated crop.jpg|thumb|Modern biology began in the nineteenth century with [[Charles Darwin]]'s work on [[evolution]] by natural selection.]]

In 1859, Charles Darwin set out his theory of evolution by natural selection as an explanation for [[adaptation]] and speciation. He defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".<ref>{{harvnb|Darwin|1859|p=[http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=side&pageseq=76 61]}}</ref> The concept was simple but powerful: individuals best adapted to their environments are more likely to survive and reproduce. As long as there is some variation between them and that variation is [[Heritability|heritable]], there will be an inevitable selection of individuals with the most advantageous variations. If the variations are heritable, then differential reproductive success leads to the evolution of particular populations of a species, and populations that evolve to be sufficiently different eventually become different species.<ref>{{harvnb|Darwin|1859|p=[http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=text&pageseq=20 5]}}</ref><ref>{{cite book |title=Strickberger's Evolution |edition=4th |author1=Hall, Brian K. |author2=Hallgrímsson, Benedikt |publisher=Jones and Bartlett |date=2008 |pages=4–6 |url=https://books.google.com/books?id=jrDD3cyA09kC&pg=PA4 |isbn=978-0-7637-0066-9 |oclc=796450355}}</ref>

[[File:Malthus 1826 vol 1 page 435 top Table England Population Growth 1780-1810.jpg|thumb|Part of [[Thomas Malthus]]'s table of [[population growth]] in England 1780–1810, from his ''[[An Essay on the Principle of Population|Essay on the Principle of Population]]'', 6th edition, 1826]]

Darwin's ideas were inspired by the observations that he had made on the [[second voyage of HMS Beagle|second voyage of HMS ''Beagle'']] (1831–1836), and by the work of a political economist, <!--the Reverend -->[[Thomas Robert Malthus]], who, in ''[[An Essay on the Principle of Population]]'' (1798), noted that population (if unchecked) [[exponential growth|increases exponentially]], whereas the food supply grows only [[linear function|arithmetically]]; thus, inevitable limitations of resources would have demographic implications, leading to a "struggle for existence".<ref>{{harvnb|Malthus|1798}}</ref> When Darwin read Malthus in 1838 he was already primed by his work as a [[Natural history|naturalist]] to appreciate the "struggle for existence" in nature. It struck him that as population outgrew resources, "favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of new species."<ref name=auto120>{{harvnb|Darwin|1958|p=[http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F1497&pageseq=124 120]}}</ref> Darwin wrote:
{{Quote|If during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organisation, and I think this cannot be disputed; if there be, owing to the high geometrical powers of increase of each species, at some age, season, or year, a severe struggle for life, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of existence, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, I think it would be a most extraordinary fact if no variation ever had occurred useful to each being's own welfare, in the same way as so many variations have occurred useful to man. But if variations useful to any organic being do occur, assuredly individuals thus characterised will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will tend to produce offspring similarly characterised. This principle of preservation, I have called, for the sake of brevity, Natural Selection.|source=Darwin summarising natural selection in the fourth chapter of ''[[On the Origin of Species]]''<ref>{{harvnb|Darwin|1859|pp=[http://darwin-online.org.uk/content/frameset?pageseq=144&itemID=F373&viewtype=side 126–127]}}</ref>}}

Once he had this [[hypothesis]], Darwin was meticulous about gathering and refining evidence of [[consilience]] to meet standards of [[scientific method|methodology]] before making his [[scientific theory]] public.<ref name="Bowler 2003" /> He was in the process of writing his "big book" to present his research when the naturalist [[Alfred Russel Wallace]] independently conceived of the principle and described it in an essay he sent to Darwin to forward to [[Charles Lyell]]. Lyell and [[Joseph Dalton Hooker]] decided to present his essay together with unpublished writings that Darwin had sent to fellow naturalists, and ''[[On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection]]'' was read to the [[Linnean Society of London]] announcing co-discovery of the principle in July 1858.<ref>{{harvnb|Wallace|1871}}</ref> Darwin published a detailed account of his evidence and conclusions in ''[[On the Origin of Species]]'' in 1859. In later editions Darwin acknowledged that earlier writers—like [[William Charles Wells]] in 1813,<ref>{{harvnb|Darwin|1866|pp=[http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F385&pageseq=21 xiv–xv]}}</ref> and [[Patrick Matthew]] in 1831—had proposed similar basic ideas.<ref>{{harvnb|Darwin|1861|p=[http://darwin-online.org.uk/content/frameset?itemID=F381&viewtype=text&pageseq=20 xiii]}}</ref> However, they had not developed their ideas, or presented evidence to persuade others that the concept was useful.<ref name="Bowler 2003" />

[[File:LA2-NSRW-3-0536 cropped.jpg|thumb|upright|[[Charles Darwin]] noted that [[Pigeon fancying|pigeon fanciers]] had created many kinds of pigeon, such as [[Tumbler pigeon|Tumblers]] (1, 12), [[Fantail pigeon|Fantails]] (13), and [[Pouter pigeon|Pouters]] (14) by [[selective breeding]].]]

Darwin thought of natural selection by analogy to how farmers select crops or livestock for breeding, which he called "[[artificial selection]]"; in his early manuscripts he referred to a "Nature" which would do the selection. At the time, other mechanisms of evolution such as evolution by genetic drift were not yet explicitly formulated, and Darwin believed that selection was likely only part of the story: "I am convinced that Natural Selection has been the main but not exclusive means of modification."<ref>{{harvnb|Darwin|1859|p=[http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=side&pageseq=21 6]}}</ref> In a letter to Charles Lyell in September 1860, Darwin regretted the use of the term "Natural Selection", preferring the term "Natural Preservation".<ref>{{cite web |url=http://www.darwinproject.ac.uk/entry-2931 |title=Darwin, C. R. to Lyell, Charles |last=Darwin |first=Charles |author-link=Charles Darwin |date=28 September 1860 |website=[[Correspondence of Charles Darwin#Darwin Correspondence Project website|Darwin Correspondence Project]] |publisher=[[Cambridge University Library]] |location=Cambridge, UK |id=Letter 2931 |access-date=1 August 2015}}</ref>

For Darwin and his contemporaries, natural selection was in essence synonymous with evolution by natural selection. After the publication of ''On the Origin of Species'',<ref name="origin">{{harvnb|Darwin|1859}}</ref> educated people generally accepted that evolution had occurred in some form. However, natural selection remained controversial as a mechanism, partly because it was perceived to be too weak to explain the range of observed characteristics of living organisms, and partly because even supporters of evolution balked at its "unguided" and non-[[orthogenesis|progressive]] nature,<ref>{{harvnb|Eisley|1958}}</ref> a response that has been characterised as the single most significant impediment to the idea's acceptance.<ref>{{harvnb|Kuhn|1996}}</ref> However, some thinkers enthusiastically embraced natural selection; after reading Darwin, [[Herbert Spencer]] introduced the phrase ''[[survival of the fittest]]'', which became a popular summary of the theory.<ref name="sotf">{{cite web |url=http://www.darwinproject.ac.uk/entry-5145#mark-5145.f3 |title=Darwin, C. R. to Wallace, A. R., 5 July (1866) |website=Darwin Correspondence Project |publisher=Cambridge University Library |location=Cambridge, UK |id=Letter 5145 |access-date=12 January 2010}}</ref><ref>{{cite journal |last=Stucke |first=Maurice E. |date=Summer 2008 |title=Better Competition Advocacy |url=http://works.bepress.com/cgi/viewcontent.cgi?article=1000&context=maurice_stucke |journal=St. John's Law Review |location=Jamaica, NY |volume=82 |number=3 |pages=951–1036 |quote=This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called 'natural selection, or the preservation of favoured races in the struggle for life.'}}—[[Herbert Spencer]], ''[https://archive.org/details/principlesbiolo05spengoog Principles of Biology]'' (1864), vol. 1, pp. 444–445</ref> The fifth edition of ''On the Origin of Species'' published in 1869 included Spencer's phrase as an alternative to natural selection, with credit given: "But the expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient."<ref>{{harvnb|Darwin|1872|p=[http://darwin-online.org.uk/content/frameset?itemID=F391&viewtype=text&pageseq=76 49].}}</ref> Although the phrase is still often used by non-biologists, modern biologists avoid it because it is [[Tautology (rhetoric)|tautological]] if "fittest" is read to mean "functionally superior" and is applied to individuals rather than considered as an averaged quantity over populations.<ref>{{cite journal |last1=Mills |first1=Susan K. |last2=Beatty |first2=John H. |year=1979 |title=The Propensity Interpretation of Fitness |url=https://mitpress.mit.edu/sites/default/files/titles/content/9780262195492_sch_0001.pdf |journal=[[Philosophy of Science (journal)|Philosophy of Science]] |volume=46 |issue=2 |pages=263–286 |doi=10.1086/288865 |citeseerx=10.1.1.332.697 |s2cid=38015862 |access-date=4 August 2015 |archive-url=https://web.archive.org/web/20151225093436/https://mitpress.mit.edu/sites/default/files/titles/content/9780262195492_sch_0001.pdf |archive-date=25 December 2015 |url-status=dead }}</ref>