The Descent of Man, and Selection in Relation to Sex
Two of his later books were devoted to the study of animal emotions and psychology; "The Descent of Man, and Selection in Relation to Sex" in 1871 and "The Expression of the Emotions in Man and Animals" in 1872. Darwin's work inspired William James's functionalist approach to psychology. Darwin's theories of evolution, adaptation, and natural selection have provided insight into why brains function the way they do.