Bates & Wallace:Mimicry Pioneers

Bates and Wallace: Mimicry and Warning Color Pioneers
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Henry Walter Bates, the son of a British stocking manufacturer, was fascinated with insects from an early age. He met and befriended another young naturalist, Alfred Russel Wallace, whom he met by accident in the Leicester Public Library while Wallace was teaching nearby in the Collegiate School. In 1847, they decided that a collecting trip "towards solving the problem of origin of species" would advance science, and could be financed by sale of specimens. They went together to explore the Amazon, its insects, birds and mammals.

   

Wallace left Bates in the Amazon after four years, survived a shipwreck, but undeterred traveled to South-east Asia on a new eight year exploration. Wallace, together with Charles Darwin, independently hit on the idea of natural selection to explain evolution.Their joint theory was published in 1858.

Bates spent an astonishing 12 years in the Amazon, but soon after the publication of Darwin's Origin of Species in 1859 he returned to England. He quickly saw that his butterflies from the Amazon supported the Darwin-Wallace argument that natural selection explains the origin of species. As he pinned out his specimens, he noted that different species, often from different families, had very similar wing coloration in any region of the Amazon. Traveling across the vast, Amazon basin, he also noted that all these species appeared to switch colors "as if by the touch of an enchanter's wand, at every few hundred miles." Bates concluded in 1862 that this "mimicry" between different butterfly species could be explained by natural selection: similarity of an edible "mimic" to a toxic "model" species improved the mimic's survival from predators. Today this kind of mimicry is called Batesian mimicry in his honour.

This was not only a good demonstration of natural selection in action, it was the first convincing example of natural selection: both Darwin and Wallace had used largely logical arguments rather than evidence. Not only that, Bates found many intermediates between Amazon butterfly species which indicated evolutionary change, showing that new species could evolve by natural selection.

Fritz MullerBates also realized that different poisonous species mimicked each other as well, forming large mimicry rings. However, the explanation had to await the Brazilian/German naturalist Fritz Müller. Müller in 1879 showed how pairs of poisonous species would also gain from mimicry: they share the cost of educating predators that they are inedible. This is today called Müllerian mimicry.

But why were poisonous species of insects so often brightly colored, with garish stripes of red, black and yellow especially common? Insects are small and vulnerable, and yet some of them appeared to be advertising their existence to predators such as birds. Darwin had a theory that bright colors were usually involved in sexual attraction, but he knew of caterpillars were sometimes also brightly colored. Since caterpillars do not engage in sex (they must morph into adult butterflies first), this did not make sense. Wallace wrote back to Darwin that these insects were indeed advertising: their inedibility. Wallace, the co-discoverer of natural selection, was also the first to explain warning colors.

Thanks to Distinguished Lecturer James Mallet for contributing to this page and to the exhibit, along with his student Nate Edelman. Find out more about the work of the Mallet Group here.