Published twelve years after Origin of Species, The Descent of Man, and Selection in Relation to Sex directly confronted the question Darwin had previously avoided: does humanity share common ancestry with other primates?
Darwin mobilized evidence from comparative embryology, rudimentary/vestigial organs, comparative physiology, and mental faculties to demonstrate that Homo sapiens descended from an ancestral primate branch.
Crucially, the book introduced Darwin’s second major evolutionary mechanism: Sexual Selection — explaining physical ornamentation, vocal courtship, and behavioral dimorphism across species that could not be explained by natural survival pressure alone.
Darwin also laid the groundwork for evolutionary psychology and anthropology, analyzing how sympathy, altruism, and social cooperation evolved as vital survival adaptations for social mammals.
