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Wrangham / Oral

On human bonding: The search for a unified theory of ape evolutionary ecology and hunter-gatherer social organization.

Richard Wrangham

     The fact that humans evolved from apes implies that human social organization may follow principles for explaining ape social organization. This conjecture has not been seriously tested, however, partly because principles explaining the great ape social systems have been uncertain. However, the comparative analysis of great ape evolutionary ecology is becoming stronger as a result of an improved understanding of the social effects of scramble competition, contest competition, the costs of motherhood, and infanticide pressure. In addition, the selective pressures influencing hunter-gatherer social ecology are becoming clearer, including the roles of hunting and cooking. Based on these developments, a unified theory may be possible, but it stumbles on an unresolved problem in the relationship between grouping and alliances within human groups. Among primates, sex differences in gregariousness tend to be correlated with sex differences in alliances: for example, among chimpanzees and spider monkeys, males are more gregarious than mothers, and form stronger intrasexual alliances. Among humans, however, mothers appear to be at least as gregarious as males, yet male-bonding is more important (has more important social consequences) than mother-bonding. In this paper, this difference between humans and other primates is attributed to the unique human combination of central-place foraging and sexually differentiated foraging strategies, with women having shorter day-ranges than men. Essentially, the requirements of central-place foraging mean that the costs of motherhood reduce women's travel distance more than they reduce women's foraging group size. Since men are able to travel further than women, they encounter invaders more often than women do. It therefore pays them to respond to the potential for contest competition by forming coalitionary bonds. These bonds are then available for use within the social group, including for political domination of women. Furthermore, the vulnerability of collected foods to being scrounged by competitors creates a pressure for mother-male bonding. Central-place foraging and sexually differentiated foraging strategies both follow from the adoption of cooking. This theory therefore suggests that male-bonding, as well as pair-bonding, have been components of the human social system since the adoption of cooking, which was certainly in place by 0.25 mya and probably began 1.88 mya."