The purpose of this book is to explore the causes of some of the most spectacular transitions in evolutionary biology, the shifts between cooperation and competition, commensalism, or parasitism. In particular, we seek to explain under what conditions such behavior as parental care, allo – parental care, and other forms of altruism among adults have evolved from the individually selfish life histories so common in animals, and how such behavior, once evolved, can be lost. Insects and arachnids provide the most varied and numerous instances and forms of the evolution of cooperation in animals; hence, they represent the most useful, though often idiosyncratic, database for analyzing social evolution.
We approach our main question, understanding the causes of the diversity of animal social systems, from the viewpoint of behavioral ecology: explaining and predicting behavior from ecology. In the context of studying sociality ‘ecology’ encompasses resource distribution in time and space, interactions with other species, and aspects of demography such as voltinism, survivorship and fecundity. Social ‘behavior’ can be defined broadly as the presence of cooperation and some form of organization, whereby the actions of individuals are coincident and coordinated or communicative in some way (Wilson 1971, p. 469). Our unifying framework for analysis in behavioral ecology is the gene's eye view of inclusive fitness theory, coupled with optimization theory (see, for example, Oster and Wilson 1978).