page_title: Coloration evidence for natural selection
section_title: Defence of Darwinism
hierarchical_section_title: Coloration evidence for natural selection / Defence of Darwinism
caption_attribution_description: 'English: Black-and-white figure of 'The Brazilian Skunk Mephitis suffocans from Edward Bagnall Poulton's The Colours of Animals 1890. Poulton introduced the term 'Aposematic' for signs like the skunk's warning coloration.
context_page_description: Animal coloration provided important early evidence for evolution by natural selection, at a time when little direct evidence was available. Three major functions of coloration were discovered in the second half of the 19th century, and subsequently used as evidence of selection: camouflage; mimicry, both Batesian and Müllerian; and aposematism.
  Charles Darwin's On the Origin of Species was published in 1859, arguing from circumstantial evidence that selection by human breeders could produce change, and that since there was clearly a struggle for existence, that natural selection must be taking place. But he lacked an explanation either for genetic variation or for heredity, both essential to the theory. Many alternative theories were accordingly considered by biologists, threatening to undermine Darwinian evolution.
  Some of the first evidence was provided by Darwin's contemporaries, the naturalists Henry Walter Bates and Fritz Müller. They described forms of mimicry that now carry their names, based on their observations of tropical butterflies.
context_section_description: Edward Bagnall Poulton's 1890 book, The Colours of Animals, renamed Wallace's concept of warning colours "aposematic" coloration, as well as supporting Darwin's then unpopular theories of natural selection and sexual selection. Poulton's explanations of coloration are emphatically Darwinian. For example, on aposematic coloration he wrote that
  At first sight the existence of this group seems to be a difficulty in the way of the general applicability of the theory of natural selection. Warning Colours appear to benefit the would-be enemies rather than the conspicuous forms themselves, and the origin and growth of a character intended solely for the advantage of some other species cannot be explained by the theory of natural selection. But the conspicuous animal is greatly benefited by its Warning Colours. If it resembled its surroundings like the members of the other class, it would be liable to a great deal of accidental or experimental tasting, and there would be nothing about it to impress the memory of an enemy, and thus to prevent the continual destruction of individuals. The object of Warning Colours is to assist the education of enemies, enabling them to easily learn and remember the animals which are to be avoided. The great advantage conferred upon the conspicuous species is obvious when it is remembered that such an easy and successful education means an education involving only a small sacrifice of life."
  Poulton summed up his allegiance to Darwinism as an explanation of Batesian mimicry in one sentence: "Every step in the gradually increasing change of the mimicking in the direction of specially protected form, would have been an advantage in the struggle for existence".
  The historian of science Peter J. Bowler commented that Poulton used his book to complain about experimentalists' lack of attention to what field naturalists (like Wallace, Bates, and Poulton) could readily see were adaptive features. Bowler added that "The fact that the adaptive significance of coloration was (sic) widely challenged indicates just how far anti-Darwinian feeling had developed. Only field naturalists such as Poulton refused to give in, convinced that their observations showed the validity of selection, whatever the theoretical problems."
caption: Warning coloration of the "Brazilian Skunk" in Edward Bagnall Poulton's The Colours of Animals, 1890
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