One of the great books of all time
Darwin's Descent of Man is one of the great books of all time.
If you haven't haven't read it (along with the Origin of Species), you haven't lived!
In the first part of the work Darwin explores the evidence for humanity's descent from primate ancestors, and, deeper in time, from the vertebrate lineage. He also deals with questions such as the place of origin of humans (he assumes, correctly, Africa), and whether the human races are sufficiently distinct as to be different species (he dismisses this argument conclusively).
The second part of the work is about sexual selection, those aspects of an organism that are not formed by natural selection (competition), but by the preferences of other members of the species in breeding choices. Darwin returns at the end of the book to humans, arguing that many features of humans are a result of sexual selection.
Two qualities epitomise this work, firstly the vast erudition of the author and the subtleties of his argument. Secondly the evident affection and compassion with which Darwin viewed all living things. Who can forget, for example, his anecdote of the male dung beetle who appeared ?highly agitated? when his mate was removed, and the female dung-beetle, who when the male was removed, stopped still and refused to move at all!