Long before the Internet, Charles Darwin established an astonishing global network of correspondents that was essential to his work: collectors and missionaries, traders and diplomats, gardeners and pigeon-breeders, and scientific workers of every kind. Without these people, most of whom received no compensation for their work, Darwin’s ideas might never have been formulated or published, and he certainly would not have been able to persuade his scientific contemporaries of the validity of his ideas.

Perhaps the most important of Darwin's correspondents was Joseph Dalton Hooker, a traveller, plant collector, and botanist who evenutally became director of the Royal Botanic Gardens at Kew. Hooker was the first man Darwin told about the theory of evolution by natural selection and became the first man of science to publicly defend Darwinism. Renowned historian and Darwin authority Jim Endersby shows how the 1300 letters the two men exchanged reveal the surprising links between science and empire, and how the private lives of these two men affected their public work, even shaping the language and philosophy of Origin of Species.