The Descent of ManCharles Darwin

Darwin's treatise on human evolution, published in 1871, twelve years after The Origin of Species. Darwin had deliberately kept the human question out of the earlier book, knowing how explosive it would be; by 1871 the intellectual climate permitted the argument he had long been prepared to make. The Descent of Man extends natural selection to the human species and adds a second evolutionary mechanism, sexual selection, which he had only briefly treated before.

The first part marshals the evidence for common descent of man and the higher apes from a shared ancestor: anatomical homologies, vestigial structures, embryological resemblances, the distribution of races. Darwin treats the origin of the moral sense, of language, and of the aesthetic faculty as natural developments from capacities already present in social animals. The second and longer part is the theory of sexual selection, developed through hundreds of pages of evidence from birds, insects, and mammals: traits that do not help an animal survive may still spread if they help it attract mates or defeat rivals. The peacock's tail is the paradigm case.

The closing chapters apply sexual selection to the human species, attempting to explain the differences between men and women, and between races, in its terms. The book completes the argument of The Origin of Species by placing man unambiguously within the history of natural life.