some striking facts and analogies, but which remains to be proven by ... more research". In 1847, he wrote to Bates that he would "like to take some one family [of beetles] to study thoroughly, ... with a view to the theory of the origin of species." Wallace planned fieldwork to test the evolutionary hypothesis that closely related species should inhabit neighbouring territories. During his work in the Amazon basin, he came to realise that geographical barriers—such as the Amazon and its major tributaries—often separated the ranges of closely allied species. He included these observations in his 1853 paper "On the Monkeys of the Amazon". Near the end of the paper he asked the question, "Are very closely allied species ever separated by a wide interval of country?" In February 1855, while working in Sarawak on the island of Borneo, Wallace wrote "On the Law which has Regulated the Introduction of New Species". The paper was published in the Annals and Magazine of Natural History in September 1855. In this paper, he discussed observations of the geographic and geologic distribution of both living and fossil species, a field that became biogeography. His conclusion that "Every species has come into existence coincident both in space and time with a closely allied species" has come to be known as the "Sarawak Law", answering his own question in his paper on the monkeys of the Amazon basin. Although it does not mention possible mechanisms for evolution, this paper foreshadowed the momentous paper he would write three years later. The paper challenged Lyell's belief that species were immutable. Although Darwin had written to him in 1842 expressing support for transmutation, Lyell had continued to be strongly opposed to the idea. Around the start of 1856, he told Darwin about Wallace's paper, as did Edward Blyth who thought it "Good! Upon the whole! ... Wallace has, I think put the matter well; and according to his theory the various domestic races of animals have been fairly developed into species." Despite this hint, Darwin mistook Wallace's conclusion for the progressive creationism of the time, writing that it was "nothing very new ... Uses my simile of tree [but] it seems all creation with him." Lyell was more impressed, and opened a notebook on species in which he grappled with the consequences, particularly for human ancestry. Darwin had already shown his theory to their mutual friend Joseph