Power asymmetry destabilizes reciprocal cooperation in social dilemmas

Direct reciprocity has been long identified as a mechanism to support the evolution of cooperation in social dilemmas. While most research on reciprocal cooperation has focused on symmetrical interactions, real world interactions often involve differences in power. Verbal theories have either claimed that power differences enhance or destabilize cooperation, indicating the need for a comprehensive theoretical model of how power asymmetries affect direct reciprocity. Here, we investigate the relationship between power and cooperation in two frequently studied social dilemmas, the prisoner's dilemma (PD) and the snowdrift game (SD). Combining evolutionary game theory and agent-based models, we demonstrate that power asymmetries are detrimental to the evolution of cooperation. Strategies that are contingent on power within an interaction provide a selective advantage in the iterated SD, but not in the iterated PD. In both games, the rate of cooperation declines as power asymmetry increases, indicating that a more egalitarian distribution of the benefits of cooperation is the prerequisite for direct reciprocity to evolve and be maintained.