Strong Reciprocity, Human Cooperation and the Enforcement of Social Norms

This paper provides strong evidence challenging the self-interest assumption that dominates the behavioral sciences and much evolutionary thinking. The evidence indicates that many people have a tendency to voluntarily cooperate, if treated fairly, and to punish non-cooperators. We call this behavioral propensity ‘strong reciprocity’ and show empirically that it can lead to almost universal cooperation in circumstances in which purely self-interested behavior would cause a complete breakdown of cooperation. In addition, we show that people are willing to punish those who behaved unfairly towards a third person or who defected in a Prisoner’s Dilemma game with a third person. This suggests that strong reciprocity is a powerful device for the enforcement of social norms like, e.g., food-sharing norms or collective action norms. Strong Reciprocity cannot be rationalized as an adaptive trait by the leading evolutionary theories of human cooperation, i.e., by kin selection theory, reciprocal altruism theory, indirect reciprocity theory and costly signaling theory. However, multi-level selection theories and theories of cultural evolution are consistent with strong reciprocity.