Joshua M. Tybur

Third party punishment (TPP) is thought to be crucial to the evolution and maintenance of human cooperation. However, this type of punishment is often not rewarded, perhaps because punishers' underlying motives are unclear. We propose that the expression of moral emotions could solve this problem by advertising such motives. In each of three experiments ( n = 1711), a third-party punishment game was followed by a trust game. Third parties expressed anger or disgust instead of, or in addition to, financial punishment. Results showed that third parties who expressed these emotions were trusted more than those who didn't express (Experiment 1), and more than those who financially punished (Experiment 2). Moreover, third parties who expressed while financially punishing were trusted more than those who punished without expressing (Experiment 3). Findings suggest that emotion expression might play a role in the evolution and maintenance of cooperation by facilitating TPP.