Coloration evidence for natural selection

Darwinists such as Alfred Russel Wallace and Edward Bagnall Poulton, and in the 20th century Hugh Cott and Bernard Kettlewell, sought evidence that natural selection was taking place.

Cott described many kinds of camouflage, and in particular his drawings of coincident disruptive coloration in frogs convinced other biologists that these deceptive markings were products of natural selection.

[5] Animal coloration, readily observable, soon provided strong and independent lines of evidence, from camouflage, mimicry and aposematism, that natural selection was indeed at work.

[6][7][8] The historian of science Peter J. Bowler wrote that Darwin's theory "was also extended to the broader topics of protective resemblances and mimicry, and this was its greatest triumph in explaining adaptations".

The attitude and very striking colour-scheme thus combine to produce an extraordinary effect, whose deceptive appearance depends upon the breaking up of the entire form into two strongly contrasted areas of brown and white.

Cott's description and in particular his drawings convinced biologists that the markings, and hence the camouflage, must have survival value (rather than occurring by chance); and further, as Cuthill and Székely indicate, that the bodies of animals that have such patterns must indeed have been shaped by natural selection.

The implication was that survival was caused by camouflage against suitable backgrounds, where predators hunting by sight (insect-eating birds, such as the great tits used in the experiment) selectively caught and killed the less well-camouflaged moths.

[15] Batesian mimicry, named for the 19th century naturalist Henry Walter Bates who first noted the effect in 1861, "provides numerous excellent examples of natural selection"[16] at work.

"[6] Inspired by On the Origin of Species, Bates realized that unrelated Amazonian butterflies resembled each other when they lived in the same areas, but had different coloration in different locations in the Amazon, something that could only have been caused by adaptation.

The evolutionary zoologist James Mallet notes that this discovery "rather illogically"[6] followed rather than preceded the accounts of Batesian and Müllerian mimicry, which both rely on the existence and effectiveness of warning coloration.

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.

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.

"[19]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".