Shared Group Memberships Mitigate Intergroup Bias in Cooperation

Research on cooperation between groups tends to consider a single social identity at a time. However, individuals naturally share group membership in one social category (e.g., religious belief) while diverging in membership to others (e.g., political ideology). Here, we test the effects of mixed-group membership on actual cooperative behavior relative to completely sharing (in-group) and completely diverging (out-group) group memberships. In three high-powered, preregistered, and incentivized experiments, we found evidence for our hypotheses that cooperation increases with the number of shared memberships in arbitrary (Experiment 1, N = 292) as well as naturally existing social categories such as political orientation and ethnicity (Experiment 2, N = 501) or political orientation and religious affiliation (Experiment 3, N = 292).