This work investigates the fundamental question of what defines humanity by examining the evolutionary trajectory, biological nature, and potential future of the human species. Richard Leakey, a renowned paleoanthropologist, and science writer Roger Lewin synthesize fossil evidence from the Lake Turkana region with behavioral observations to construct a comprehensive narrative of human development. The authors argue that human nature is not a static biological constant but a product of specific environmental pressures and social adaptations that have shaped our ancestors over millions of years.

The text provides a dense, scholarly overview of human evolution that remains accessible to readers interested in the intersection of biology and anthropology. Its reliance on specific archaeological findings from the Leakey expeditions offers a grounded perspective on the complexities of our evolutionary history.