The Garden of Eden as the ideal and untouched site of life's creation persists in popular thought, even as we have uncovered a lengthy fossil record and developed a scientific understanding of evolution. The continent of Africa is a good candidate for Eden: its generally warm climate, rich vegetation, and variety of animal species lend themselves easily to such a comparison. Yet in the time since the first primates appeared millions of years ago, Africa has undergone profound alterations in physical geography, climate, and biota.

Linking the evidence of the past with that of the present,...