The Evolution of Helping.
II. The Role of Behavioral Conflict

Emlen, S.T. (1982). American Naturalist, 119:40-53.

In part I (Emlen, 1982), an ecological constraints model was developed to predict the circumstances under which grown offspring would remain in familial units with their parents. Such retention was considered a necessary, but not sufficient, condition for the evolution of helping behavior.

Whether or not non-breeding auxiliaries will participate as helpers in such groups will depend upon the costs and benefits of such helping, measured from the viewpoints of both breeder and helper. In this paper, these costs and benefits are formalized, and the conclusion is reached that conflict frequently is to be expected between breeder and auxiliary over the behavioral role of the latter.

When ecological constraints favor grown offspring remaining at home, but the retention of such individuals depresses the fitnesses of the breeders, helping by an auxiliary may evolve as a means of reducing the incremental cost to the breeder, and thus of minimizing the likelihood that the auxiliary will be expelled from the group.

More commonly, however, helping leads to an asymmetrical gain to the breeder. Conflict in the opposite direction may occur, with breeders favoring continued retention of older auxiliaries as helpers beyond the point at which such auxiliaries would maximize their inclusive fitness by leaving and initiating breeding on their own. Various possible "resolutions" to such breeder-helper conflicts are discussed, including behavioral manipulation of auxiliaries by more dominant breeders, and three forms of fitness forfeiting by breeders (via shared paternity, communal maternity, and reciprocity).

The type of conflict expected, as well as the form of its resolution, will be influenced by the consistency and predictability with which ecological constraints preclude the chance for independent establishment and breeding by auxiliaries. When environmental conditions are stable from year to year and such preclusion is the rule, reproductive competition will be severe and challenges between subordinates and dominants over breeding status are expected. When environmental conditions are variable and unpredictable from year to year, auxiliaries will be less constrained to remain as helpers and dominant breeders are predicted to adopt fitness forfeiting measures to recruit their continued services.

Finally, it is argued that behavioral conflicts, and their resolutions, have been of major importance in the evolution of ever-increasing complexity in the structure of animal societies.