Beyond Reciprocity: Common Knowledge of Social Identity Enhances the Intrinsic Value of Ingroup Trust

People are often more willing to help or trust members of their own groups as opposed to other groups. This prosociality could reflect intrinsic value placed on acts of ingroup cooperation or a strategic expectation that ingroup members will cooperate more and provide tangible gains. A key line of evidence for the strategic view is that people show more ingroup favoritism when both parties are aware of shared group membership, which means they can each expect more favorable treatment. However, common knowledge of shared identity may also make interactions feel more meaningful. Here, we provide evidence that the effects of membership knowledge need not reflect strategic expectations alone but can also reflect the intrinsic value of ingroup cooperation. Across three experiments, participants played multiple one-shot trust games with ingroup and outgroup trustees. For each trust decision, participants were aware of the exact proportion of times trustees from a given group had reciprocated trust; this likelihood of reciprocity was held constant between ingroup and outgroup trustees. Although expectations of reciprocity were thus known and held constant, participants preferred to trust ingroup members over outgroup members, and this bias was amplified when participants believed trustees knew about their shared group membership. These results suggest that ingroup members cooperate more when they are aware of each other’s social identity not only because it increases their expectations of obtaining tangible gains but also because it boosts the intrinsic social value of cooperating with a fellow ingroup member.