Darwin played an important role in the controversy over vivisection that broke out in late 1874. Public debate was sparked when the Royal Society for the Prevention of Cruelty to Animals brought charges against a French physiologist who had performed vivisection on dogs at the British Medical Association congress in Norwich. The prosecution was unsuccessful, but it gave rise to a series of campaigns to increase public awareness about experiments on live animals in Britain. In December 1874, Darwin was asked to sign a memorial by the writer and social reformer Frances Power Cobbe. It called upon the RSPCA to investigate the nature and scope of vivisections performed in physiology laboratories and teaching hospitals, and to draft legislation that would protect animals from suffering. Darwin was sympathetic to the cause, but found some of Cobbe's rhetoric inflammatory, and he strongly objected to her criticism of the eminent physiologist Rudolf Virchow. He explained his position to his daughter Henrietta: ‘I certainly could not sign the paper sent me by Miss Cobbe, with its monstrous (as it seems to me) attack on Virchow for experimenting on the Trichinae’ (letter to H. E. Litchfield, 4 January [1875]). Darwin also worried that any bill passed by a House of Commons largely ignorant of science might halt the progress of physiology. He reiterated these concerns in a letter to Thomas Henry Huxley ten days later, urging him to work with other physiologists to present their own petition (letter to T. H. Huxley, 14 January 1875). In the event, Darwin became closely involved with the drafting of alternative legislation. Over the course of several months, he wrote dozens of letters to leading experimenters, physicians, surgeons, and public officials, and drew on his own family circle for assistance in preparing a bill for Parliament.

Darwin almost never involved himself in public controversy and so the extent of his activity in the vivisection affair is surprising. His own research on animals relied primarily on comparative anatomy, including dissection, and natural-historical observation. But he had drawn extensively on the work of physiologists in his study of emotional expression, and in his most recent research on insectivorous plants.