“This provocative, important book outlines an evolutionary theory of altruism, examining past theoretical problems–in particular, how to distinguish altruism and selfish (or hedonistic) motives. Drawing deeply and judiciously on research in theoretical biology, social psychology, philosophy, and anthropology, Sober and Wilson–both long-standing and eminent participants in controversies about the evolution of altruism–make two major claims: first, that ‘natural selection is unlikely to have given us purely egoistic motives,’ second, that the much-maligned concept of group selection–the idea that natural selection sometimes operates at the level of the group–may be a mechanism for the evolution of altruism…Readers will be impressed by the breadth of the analysis and, especially, the extraordinary clarity of the presentation. This will most likely be regarded as a landmark, if controversial, work. It is a testament to the authors’ understanding and skill as writers that it is also fun to read.”