Powering Up with Indirect Reciprocity in a Large-Scale Field Experiment

The evolution of cooperation via indirect reciprocity has been a topic of great interest in recent years. Mathematical models and computer simulations have demonstrated the power of indirect reciprocity for promoting cooperative behavior (1-23). This body of theoretical work is supported by behavioral experiments where subjects play economic games in the laboratory. People are substantially more cooperative when their decisions are observable, and when others can respond accordingly (24-43). Subjects understand that having a good reputation is valuable in these settings (32), and so are willing to pay the cost of cooperation. Observability particularly increases cooperation when the prosocial nature of the cooperative choice is made salient (38, 44). Moreover, experimental evidence indicates that indirect reciprocity is deeply entrenched in human psychology: subtle cues of observability have large effects on cooperation levels (45-48), and our initial impulse to cooperate in one-shot anonymous settings is likely the result of adaptation in a world dominated by reputational concerns (49, 50). These laboratory experiments generate powerful insights into human psychology, and provide clear evidence for the importance of indirect reciprocity. However, they typically employ abstract economic games and involve the interaction of only a handful of subjects. Thus the question of whether observability effects large-scale cooperation in real world settings outside of the laboratory remains largely unexplored (exceptions include (51-53)). The extent to which findings from theory and the lab generalize to natural field settings is of great importance, both for scientific understanding and for public policy (54).