This paper studies how competition between groups affects cooperation. In the control condition, pairs of subjects play an indefinitely repeated Prisoner's Dilemma game without external competition. In the treatment, two pairs compete against each other. No monetary rewards are tied to winning,...

Social interactions predominantly take place under the shadow of the future. Previous literature explains cooperation in indefinitely repeated prisoner's dilemma as predominantly driven by self-interested strategic considerations. This paper provides a causal test of the importance of social...