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Abstract

Testosterone plays a key role in shaping human social behavior. Recent findings have linked testosterone to altruistic behavior in economic decision tasks depending on group membership and intergroup competition. The preferential treatment of ingroup members, while aggression and discrimination is directed towards outgroup members, has been referred to as parochial altruism. Here we investigated in two consecutive studies, whether testosterone is associated with parochial altruism depending on individual tendency for costly punishment. In the first study, 61 men performed a single-shot ultimatum game (UG) in a minimal group context, in which they interacted with members of an ingroup and an outgroup. In the second study, 34 men performed a single-shot UG in a more realistic group context, in which they responded to the proposals of supporters of six political parties during the German election year 2017. Political parties varied in their social distance to the participants' favorite party as indicated by an individual ranking, which resulted in one ingroup (rank 1) and five outgroups of varying social distance (rank 6 referred to as the most distant outgroup). Participants also performed a cued recall task, in which they had to decide whether they had already encountered a face during the UG (oldnew decision). In both studies, results showed a parochial pattern with higher rejection rates of outgroup than ingroup offers. Interestingly, higher salivary testosterone was associated with higher rejection rates related to unfair offers by the most distant outgroup, yet only in the group of self-oriented subjects (pro-selfs). Further, only the pro-selfs showed a memory advantage for unfair interaction partners in study 2, especially if those were ingroup members. The present findings suggest that the latent intergroup bias during decision-making, that was particularly visible in pro-selfs, may be related to endogenous testosterone. In line with previous evidence that already indicated a role of testosterone in shaping male parochial altruism in male soccer fans, these data underscore the general yet rather subtle role of testosterone also in other social settings.