W.D. Hamilton is considered by many the most important theoretical biologist of the 20th century. He has made major discoveries in evolutionary biology, genetics, and social behavior, and his essays continue to exert tremendous influence throughout the discipline. This second volume of his collected papers focuses on his groundbreaking work on sex and sexual selection. It contains the 18 papers he published between 1980 and 1991, many of them examining the role of parasites and disease in promoting genetic diversity. For each paper, Hamilton has written an accessible introduction describing why the work was done, how the paper came to be written, and its eventual fate. An invaluable collection for biologists, this book also provides general readers with deep insights into the sometimes surprising mechanics of evolutionary processes.