Spillover effects of third-party punishment on cooperation: A norm-based explanation

stronger incentive to defect. However, the results revealed a significantly higher cooperation level in LC. A plausible explanation is that the defection cost in form of punishment served as a norm reminder, but cost in form of tax lacked this function, implying that even defectors are not necessarily benefit maximizers. The results of Experiment 2 confirmed this explanation: compared with unpunished defectors, the punished ones manifested a higher level of norm activation. The bootstrap analysis showed that the norm activation completely mediated TPP and cooperation. Experiment 2 also found a spillover effect of TPP: the punished defectors still demonstrated a high cooperation in a new different game where the sanction was absent. Finally, Experiment 3 found another spillover effect of TPP: bystanders who did not experience the punishment in person but witnessed it showed a significantly higher cooperation in subsequent interactions. In conclusion, oftentimes, people defect simply because they are unaware of the existence of a certain norm, and activating people’s norms through TPP can significantly reduce their selfish behaviors. In addition to being an economic means to reduce defectors’ payoff, TPP serves as a norm reminder. The two spillover effects found in this study suggest that TPP as a means of norm activation may be more efficient than as an economic means because of its cost-effectiveness. These findings shed new light on the understanding of extensive cooperation among genetically unrelated individuals.