Evolutionary theory and the human family.

Emlen's (1995) paper "An evolutionary theory of the family" reviewed existing ideas about the nature of family systems and the reasons why they have evolved in certain animal species. His theorizing led him to propose 15 predictions about how family systems function, based on favorable evidence from various species, mostly birds. While he suggested that these predictions can be applied to the human case, he himself did not attempt to do so. We consider the applicability of Emlen's 15 predictions to the study of human family systems, and find that several aspects of the life history and ecology of Homo sapiens require that they be modified. These considerations include: (1) the importance of intragroup solidarity in the context of intergroup competition: unlike in many other species where dispersal constraints arise from food or breeding site shortages, the primary pressure driving human sociality seems to be competition from other human groups; (2) the complex nature of exchange and reciprocity in human society: reciprocal altruism in particular is integral to human social interaction and leads to a particularly high degree of non-nepotistic helping behavior; and (3) the implications of menopause and the existence of potentially dominant, postreproductive helpers: helpers of this sort have little incentive to disperse or to encourage offspring to disperse, thus greatly increasing family stability.