The problem of opportunity

Cultural group selection theorists propose that humans evolved prosocial preferences. These claims revolve largely around the centrality of punishment in cultural groups, which helped to eliminate free riders. The purpose of this paper is to explore whether distinguishing between free-riding as an action, and free riders as entities, undermines or supports this view. I develop three individual-based models of the Prisoner’s Dilemma. The first model shows that strong reciprocity removes overt free-riders from a population, and maintains a high rate of cooperation. In the second, I introduce individuals that mimic cooperative preferences, but who defect when they trick opponents into cooperating. I show that strong reciprocity is robust against this strategy, but not because individuals are replaced by strong reciprocators. Finally, I introduce a third strategy, covert mimicry, where some mimics may defect without detection. I draw attention to the problem highlighted in these models, which is that cooperation may be maintained in populations only because free riders are not presented with the opportunity to defect. I discuss this problem in the context of cultural group selection and the human capacity for innovation, and suggest that hypotheses relying on prosocial preferences for maintaining cooperation require some revision.