I just finished reading Last Ape Standing: The Seven-Million-Year Story of How and Why We Survived.
Author Chip Walter provides an intriguing general overview of our best current understanding of human evolution (including the startling proposition that there have been at least 27 species of what we would call “human”). He explores the possible reasons why we homo sapiens are the last surviving humans, and tackles the thornier-than-you-might-think problem of what exactly sets us aside from our nearest living cousins (chimps, gorillas, etc.).
This is the kind of book that needs to be written every ten years; perhaps more often–the amount of data and the latest speculation on evolutionary specifics change that quickly. (For example, scientists once thought we might have descended from Neanderthals; now they are certain that that is not the case, that we share a common ancestor with Neanderthals, that we coexisted with them for millennia, and probably even mated with them!)