Although Charles Darwin’s On the Origin of Species introduced his theory of evolution to the world, it did not extend this theory to the evolution of humans. Darwin saved this task for The Descent of Man, which appeared 12 years later in 1871. Nevertheless, Darwin’s theories about human evolution were clearly telegraphed in his earlier work—and made explicit by other writers in the intervening years—so The Descent of Man was far from unexpected. The text addressed not only the physical trajectory of evolution but also the development of intellect and morality in humankind. This is the first American edition, printed in the same year as the first English edition.