On this date, the English entomologist Henry Walter Bates was born. Bates became friends with Alfred Russel Wallace when the latter took a teaching post in the Leicester Collegiate School. Wallace was also a keen entomologist, and he had read the same kind of books as Bates had, and as Darwin, Huxley and no doubt many others had – Thomas Malthus on population, James Hutton and Charles Lyell on geology, Charles Darwin’s Voyage of the Beagle, and above all, the anonymous Vestiges of the Natural History of Creation, which put evolution into everyday discussion among literate folk. They also read William H. Edwards on his Amazon expedition, and this started them thinking that a visit to the region would be exciting, and might launch their careers. Bates accompanied Wallace on an expedition to the Amazon in 1848.
Whereas Wallace returned to England after four years in South America and then went on to Indonesia, Bates stayed in the Amazon for eleven years but continued to correspond with him, encouraging Wallace’s developing theories on organic evolution. Bates discovered that closely related species often were separated geographically by rivers, and later realized that this was evidence of geographical speciation. His 1862 study of color patterns in butterflies established what is now called Batesian mimicry, in which non-poisonous animals mimic the bright warning coloration of poisonous animals. Bates argued that this kind of mimicry could not be produced by Lamarckian use-inheritance and was clear evidence of selection. In his book The Naturalist on the River Amazons (1863), he wrote:
… on these expanded membranes [i.e., butterfly wings] Nature writes, as on a tablet, the story of the modifications of species, so truly do all changes of the organisation register themselves thereon. Moreover, the same colour-patterns of the wings generally show, with great regularity, the degrees of blood-relationship of the species. As the laws of nature must be the same for all beings, the conclusions furnished by this group of insects must be applicable to the whole world.
Bates assumed the post of Assistant Secretary of the Royal Geographical Society in 1864 where he edited the society’s Transactions and organized expeditions. He was elected a Fellow of the Royal Society of London in 1881.