The Descent of Man, and Selection in Relation to Sex
Two of his later books, "The Descent of Man, and Selection in Relation to Sex" (1871) and "The Expression of the Emotions in Man and Animals" (1872) explore the subject of psychological differences between the sexes. "The Descent of Man and Selection in Relation to Sex" includes 70 pages on sexual selection in human evolution, some of which concerns psychological traits.