The evolution of cooperative breeding is complex, and particularly so in humans because many other life history traits likely evolved at the same time. While cooperative childrearing is often presumed ancient, the transition from maternal self-reliance to dependence on allocare leaves no known empirical record. In this paper, an exploratory model is developed that incorporates probable evolutionary changes in birth intervals, juvenile dependence, and dispersal age to predict under what life history conditions mothers are unable to raise children without adult (...) cooperation. The model’s outcome variable (net balance) integrates dependent children’s production and consumption as a function of varying life history parameters to estimate the investment mothers or others have to spend subsidizing children. Results suggest that maternal-juvenile cooperation can support the early transition toward a reduction in birth intervals, a longer period of juvenile dependence, and having overlapping young. The need for adult cooperation is most evident when birth intervals are short and age at net production is late. Findings suggest that the needs of juveniles would not have been an early selective force for adult cooperation. Rather, an age-graded division of labor and the mutual benefits of maternal-juvenile cooperation could be an important, but overlooked step in the evolution of cooperative breeding. (shrink)

I present evidence that humans have evolved convergently to social insects with regard to a large suite of social, ecological, and reproductive phenotypes. Convergences between humans and social insects include: (1) groups with genetically and environmentally defined structures; (2) extensive divisions of labor; (3) specialization of a relatively restricted set of females for reproduction, with enhanced fertility; (4) extensive extramaternal care; (5) within-group food sharing; (6) generalized diets composed of high-nutrient-density food; (7) solicitous juveniles, but high rates of infanticide; (8) (...) ecological dominance; (9) enhanced colonizing abilities; and (10) collective, cooperative decision-making. Most of these convergent phenotypic adaptations stem from reorganization of key life-history trade-offs due to behavioral, physiological, and life-historical specializations. Despite their extensive socioreproductive overlap with social insects, humans differ with regard to the central aspect of eusociality: reproductive division of labor. This difference may be underpinned by the high energetic costs of producing offspring with large brains. (shrink)

Matriliny has long been debated by anthropologists positing either its primitive or its puzzling nature. More recently, evolutionary anthropologists have attempted to recast matriliny as an adaptive solution to modern social and ecological environments, tying together much of what was known to be associated with matriliny. This paper briefly reviews the major anthropological currents in studies of matriliny and discusses the contribution of evolutionary anthropology to this body of literature. It discusses the utility of an evolutionary framework in the context (...) of the first independent test of Holden et al.’s 2003 model of matriliny as daughter-biased investment. It finds that historical daughter-biased transmission of land among the Mosuo is consistent with the model, whereas current income transmission is not. In both cases, resources had equivalent impacts on male and female reproduction, a result which predicts daughter-biased resource transmission given any nonzero level of paternity uncertainty. However, whereas land was transmitted traditionally to daughters, income today is invested in both sexes. Possible reasons for this discrepancy are discussed. (shrink)