Kim Hill

We would like to thank the commentators for their generous comments, valuable insights and helpful suggestions. We begin this response by discussing the selfishness axiom and the importance of the preferences, beliefs, and constraints framework as a way of modeling some of the proximate influences on human behavior. Next, we broaden the discussion to ultimate-level (that is evolutionary) explanations, where we review and clarify gene-culture coevolutionary theory, and then tackle the possibility that evolutionary approaches that exclude culture might be sufficient to explain the data. Finally, we consider various methodological and epistemological concerns expressed by our commentators.

Researchers from across the social sciences have found consistent deviations from the predictions of the canonical model of self-interest in hundreds of experiments from around the world. This research, however, cannot determine whether the uniformity results from universal patterns of human behavior or from the limited cultural variation available among the university students used in virtually all prior experimental work. To address this, we undertook a cross-cultural study of behavior in ultimatum, public goods, and dictator games in a range of small-scale societies exhibiting a wide variety of economic and cultural conditions. We found, first, that the canonical model – based on self-interest – fails in all of the societies studied. Second, our data reveal substantially more behavioral variability across social groups than has been found in previous research. Third, group-level differences in economic organization and the structure of social interactions explain a substantial portion of the behavioral variation across societies: the higher the degree of market integration and the higher the payoffs to cooperation in everyday life, the greater the level of prosociality expressed in experimental games. Fourth, the available individual-level economic and demographic variables do not consistently explain game behavior, either within or across groups. Fifth, in many cases experimental play appears to reflect the common interactional patterns of everyday life.

Experimental measurements of the efficiencies of traditional wooden versus modern metal tools among Machiguenga women of the Manú River Basin indicate that individuals using wooden tools spend two to three times as many minutes digging and peeling one kilogram of manioc as they spend when using machetes and knives. However, because Machiguenga women can acquire enough manioc in one hour to feed twenty-five adults for one day, a two- to threefold adjustment in the time spent digging and peeling with traditional tools to compensate for lower efficiency leads to only a minor difference in the absolute time spent daily in subsistence tasks. On the other hand, the adoption of metal tools by indigenous women may lead to important changes in women's time allocation to subsistence work and their dietary contribution when root digging and peeling rates are significantly lower than the ones found among Machiguenga women; for example, in foraging societies dependent upon wild tubers. This study shows that experimentation is a useful tool for measuring and predicting the effects of modern technology on the sexual division of labor across ecological contexts.