The year 1871 was an extremely busy and productive one for Darwin, with the publication in February of his long-awaited book on human evolution, Descent of man. The other main preoccupation of the year was the preparation of his manuscript on expression. Darwin continued to investigate the mechanisms of various emotions, such as grief, shame, and astonishment, drawing on the expertise of physicians and physiologists, as well as zoo-keepers, pet owners, parents of young children, and professional photographers. The year also brought a significant milestone for the family, as Darwin's eldest daughter Henrietta was married in August.

The year 1870 is aptly summarised by the brief entry Darwin made in his journal: 'The whole of the year at work on the Descent of Man & Selection in relation to Sex'. Descent was the culmination of over three decades of observations and reflections on human ancestry, including the origin of language, mind, morals, and religious temperament. The year was otherwise coloured by controversies, including vigorous objections to the application of natural selection to humans from Wallace and St George Jackson Mivart.