Why is `blood thicker than water'? Are we innately violent or pacific? Why are plants and animals sexual? Why do we grow old and die? Such questions have motivated the life-work of W.D. Hamilton, widely acknowledged as the most important theoretical biologist of the 20th century. His papers continue to exert an enormous influence and they are now being republished for the first time. This first volume contains all of Hamilton's publications prior to 1981, a set especially relevant to social behavior, kinship theory, sociobiology, and the notion of `selfish genes'. Each paper is introduced by an autobiographical essay written especially for this collection. Accessible to non-specialists, this fascinating volume features several of the most read and famous papers of modern biology.