Mayr’s distinction between proximate and ultimate explanation is justly famous, marking out a division of explanatory labor in biology. But while it is a useful heuristic in many cases, there are others in which proximate factors play an important role in shaping evolutionary trajectories, and in such cases, each project is sensitive to, and relevant to, the other. This general methodological claim is developed in the context of a discussion of human cooperation, and in particular, in a discussion on the (...) puzzling stability of the social contract over the Pleistocene–Holocene transition. For I argue that while we have a plausible account of the stability of Pleistocene cooperation, the stabilizing factors of the Pleistocene disappear in the Holocene, but cooperation does not. Holocene humans solved many collective action problems; cooperation did not collapse despite the apparent growth of free-riding elites. So the article combines a methodological claim about the interaction of proximate and evolutionary biology with a substantive one about the ecology of human cooperation. (shrink)

In this article I develop a big picture of the evolution of human cooperation, and contrast it to an alternative based on group selection. The crucial claim is that hominin history has seen two major transitions in cooperation, and hence poses two deep puzzles about the origins and stability of cooperation. The first is the transition from great ape social lives to the lives of Pleistocene cooperative foragers; the second is the stability of the social contract through the early Holocene (...) transition to complex hierarchical societies. The first of these transitions is driven, at least initially, by individual advantage: cooperation paid off for individual foragers, initially through mutualist interaction, then through reciprocation. This argument leads to a reanalysis of the role of violence and the nature of the freeriding threat to cooperation. But the conditions that select for cooperative individuals in the Pleistocene were eroded in the Pleistocene–Holocene transition. So we need an alternative account of the survival, and indeed the expansion, of cooperation in the Holocene. Group selection driven by intercommunal conflict really may well be central to this second transition. (shrink)