This ‘hidden gem’ from 1887 published in the Proceedings of the Zoological Society of London, the predecessor of Journal of Zoology, is an article written by E.B. Poulton about aposematism before he actually introduced the term in his book The Colours of Animals, published in 1890. It is essentially a review article summarising, comparing and discussing the existing data from various experiments testing Alfred Russel Wallace’s original idea of the use of warning colours in prey to put off predators from attacking them.
The article begins with a brief history of the idea, originating from correspondence between Darwin and Wallace. Puzzled by bright, conspicuous colours in caterpillars which could not possibly be explained by sexual selection, Darwin asked Wallace to suggest some other explanation and adaptive value for these bright colours. Wallace proposed that, as Poulton put it, ‘the gaudy colouring acts as an indication of something unpleasant about its possessor’, such as a nauseous taste or smell, and it would thus be to the advantage of the prey to be as conspicuous as possible to warn experienced predators of their foul qualities. Wallace’s idea had subsequently been tested and proven plausible. However, in this paper, Poulton points out that ‘the acquisition of an unpleasant taste or smell, together with a conspicuous appearance, is so simple a mode of protection, and yet ex hypothesi so absolutely complete, that it seems remarkable that more species have not availed themselves of this means of defence. What can be the principle which works in antagonism to such a mode of protection?’ As one explanation, Poulton proposes that this strategy would become less effective the more common it becomes among the prey, as predators might then start eating the foul-tasting prey if they would otherwise starve. It was indeed Poulton who introduced the idea of frequency-dependent selection in his later work, but he was clearly already contemplating this idea when he wrote this article.
This paper acts as a wonderful summary of the development of the theory of aposematism and is teeming with references to Wallace and Darwin as well as other famous names such as Bates and Müller regarding their respective theories on mimicry. It is available for free in our ‘Hidden Gems’ section of the Journal of Zoology website.