The Descent of Man, an Selection in Relation to Sex is a book on evolutionary theory by English naturalist Charles Darwin, first published in 1871. It was Darwin's second large book on evolutionary theory, following his 1859 work, The Origin of Species, and is concerned with outlining the application of Darwin's theory to human evolution, and detailing the theory of sexual selection. The book touches on a number of related issues, including evolutionary psychology, evolutionary ethics, differences between human races, differences between human sexes, and the relevance of the evolutionary theory to society.