Darwin recognised that the evolution of cooperative societies in animals and man posed an important challenge to his theory of natural selection. If resources are limited and individuals compete to breed, why is cooperative behaviour so widespread? Hamilton's extension of the theory of natural selection to incorporate the effects of cooperation on non-descendant kin provides the framework for our current understanding of animal societies. This issue brings together fifteen leading evolutionary biologists working on micro-organisms, social insects, birds, mammals and man in an attempt to synthesise our current understanding of the evolution of societies.
Separate papers cover the theoretical framework used to explain cooperative behaviour, the definition of organisms, social evolution in micro-organisms, the evolution of insect societies and the origin of eusociality, the distribution of cooperative breeding in birds and mammals and the relative importance of nepotistic behaviour and reciprocity in non-human primates, while four final papers review our understanding of hominid and human societies. The issue provides an up-to-date synthesis and review of a modern interpretation of the evolution of cooperative behaviour and cooperative societies in non-human animals. The papers show how selection operating through variation in inclusive fitness can favour cooperative strategies; how cooperation and competition interact; and how the behaviour of individuals modifies the structure of groups and breeding systems. The four final chapters on hominids and humans then explore the extent to which a similar approach can account for human behaviour and the structure of human societies. The papers are accessible to non-specialists and should help to provide the basis for a synthetic theory of the evolution of society.