Designed for a one term introduction to the modern theory of evolution by natural selection and how that theory explains animal social behavior in general and human sociocultural evolution in particular. The book can be used in courses in Biology, Anthropology, Psychology, and Sociology, as well as in courses in Economics and Law that seek to include a biological evolutionary perspective. The book is based upon the teaching experiences of two general biologists who have taught these subjects to students at Amherst College and Yale University for many years. It provides a balanced and engaging account of the important theories and concepts of evolution and how they contribute to our understanding of human behavior and history.