The standard theories of cooperation in humans, which depend on repeated interaction and reputation effects among self-regarding agents, are inadequate. Strong reciprocity, a predisposition to participate in costly cooperation and the punishment, fosters cooperation where self-regarding behaviors fail. The effectiveness of socially coordinated punishment depends on individual motivations to participate, which are based on strong reciprocity motives. The relative infrequency of high-cost punishment is a result of the ubiquity of strong reciprocity, not its absence.

Guala does not go far enough in his critique of the assumption that human decisions about sharing made in the context of experimental game conditions accurately reflect decision-making under real conditions. Sharing of hunted animals is constrained by cultural rules and is not as assumed in models of weak and strong reciprocity. Missing in these models is the cultural basis of sharing that makes it a group property rather than an individual one.