TY - RPRT A1 - Kölle, Felix A1 - Quercia, Simone A1 - Tripodi, Egon T1 - Social Preferences under the Shadow of the Future N2 - 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 preferences for cooperation, varying the composition of interactions to be either homogeneous or heterogeneous in terms of these preferences. Through a series of pre-registered experiments (N = 1,074), we show that groups of prosocial individuals achieve substantially higher levels of cooperation. The cooperation gap between prosocial and selfish groups persists even when the shadow of the future is increased to make cooperation attractive for the selfish and when common knowledge about group composition is removed. Y1 - 2023 U6 - https://doi.org/10.2139/ssrn.4506320 ET - CESifo Working Paper No. 10534 ER -