Conflicting identities and cooperation between groups: experimental evidence from a mentoring programme.

Well-functioning human societies require the integration of vulnerable minorities, yet leading scientific theories conflict on how easily diverse groups cooperate. We experimentally investigate cooperation in 14 centres of a mentoring programme where participants have two possible natural identities-individuals raised under legal guardianship, suffering a negative stereotype (; 112) and users without such a social stigma (; 82). Participants played a prisoners' dilemma game with an anonymous partner from the same centre (centre-ingroup) and from another centre (centre-outgroup). For individuals without a history within-centre interaction, we find centre-outgroup favouritism among and centre-ingroup favouritism among . However, the longer individuals have been in the centre the more centre-ingroup favouritism they display, while the opposite is true for . Regardless of within-centre history, both and individuals cooperate less with the centre-ingroup (versus outgroup) as the probability that the centre-ingroup is increases. Thus, we observe patterns of centre-outgroup and natural-outgroup favouritism among which challenge theoretical frameworks exclusively focusing on ingroup favouritism. Our findings highlight the roles of system-justification and stereotypes in intergroup cooperation and have implications for the integration of vulnerable groups and the optimization of social policy programmes.