ABSTRACT
One paradox in animal social biology is that groups composed of individuals of relatively high biological complexity tend to have a relatively low degree of cohesiveness and integrated action (Wilson, 1975a). Although individuals in vertebrate societies may forage in groups, communicate information about the presence of a predator and actively defend vulnerable group members, there appears to be little specialization in the behavioral repertories of individuals. In the vast majority of vertebrate societies there are no castes, or groups of age-or size-correlated specialists in reproduction, offspring care, defense and foraging. Indeed, in vertebrate groups individuals attempt to maximize their own reproductive success within a social framework rather than maximize the fitness of the group as a whole. Kin-selected cooperation or reciprocally altruistic relationships among group members may add an additional tier of interaction and level of complexity. Socioecological studies have shown that vertebrate group structure, measured in terms of group size, composition and mating systems, is adaptive (reviewed in Krebs & Davies, 1992). Nevertheless, the organization of a vertebrate social group is still largely a consequence of the selfish reproductive interests of its members. Natural selection has not acted to favor an adaptive structure of the group as a whole.
