LAUSR

Abstract Moral emotions (i.e. guilt, shame) and interpersonal processes such as fairness have been theorised to facilitate cooperation within society. However, empirical tests to support this association have yielded inconsistent results. The present research investigated whether guilt and shame have an impact on fairness-related decision-making and reciprocity-driven cooperation. College students (N = 94) were assigned to one of three experimental conditions (Guilt vs. Shame vs. Control) and instructed to complete an iterated Ultimatum Game against two anonymous partners. We manipulated social context so that one partner would appear as predominantly fair, and the other as predominantly unfair. For guilt, we found that participants (assigned as proposers) reciprocated fair partners with significantly larger amounts of money (i.e. positive reciprocity). For shame, we found that participants had higher rejection rates of unfair splits, and subsequently offered less money to unfair partners (i.e. negative reciprocity). We argue that both guilt and shame benefit fairness-related judgments, guilt by endorsing fairness, and shame by punishing unfairness. Our results also show that guilt and shame benefit reciprocity-driven cooperation, although they do so via different pathways. Our findings suggest that guilt promotes cooperation via positive reciprocity, whereas shame stabilises cooperation via negative reciprocity.