In 1871 he examined human evolution and sexual selection in The Descent of Man, and Selection in Relation to Sex, followed by The Expression of the Emotions in Man and Animals (1872).
Pada tahun 1871 ia memeriksa evolusi manusia dan seleksi seksual dalam The Descent of Man, and Selection in Relation to Sex, diikuti oleh The Expression of the Emotions in Man and Animals.