Includes bibliographical references and index.

"Why is the evolution of social behaviour interesting? For one thing, if we wish to comprehend the origin, maintenance and functionality of any biological trait, we need to understand its evolution. At the same time, each behaviour is social in essence; it affects the survival, production and reproduction of others in some way or another. "Others" encompasses social partners including mates, offspring, competitors, friends and foes regardless. But what is it that brings animals together? Why are individuals attracted by others, interact with them or form groups? What explains the staggering diversity of animal social systems? To start to address these questions it seems useful to distinguish between ecological causes and the functions of social behaviour. For instance, it may be safer to be in a group because of high predation pressure, which represents an ecological cause for social contact, or it may be beneficial to aggregate to choose a mating partner, which is a functional reason for social attraction. Obviously, ecological causes and social functions can be intertwined. In any case, living together entails competition for resources and involves different types of interactions between conspecific contenders, which show different functional characteristics and fulfil different roles (Wilson 1975)"--