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 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. Participants of study 2 also performed a cued recall task, in which they had to decide whether they had already encountered a face during the previous UG (old-new decision). In order to make the UG data of study 2 most comparable to the data of study 1, the rejection rates of several parties were combined according to the social distance ranking they achieved. Parties ranked 1 to 3 formed the relatively close and favored ‘ingroup’ that shared similar political values with the participant (e.g., left wing parties), while the ‘outgroup’ consisted of parties ranked from 4 to 6 with more distant or even antagonistic political views (e.g., conservative to right wing parties). In both studies, results showed a parochial pattern with higher rejection rates made in response to outgroup compared to ingroup offers. Interestingly, across studies higher salivary testosterone was associated with higher rejection rates related to unfair outgroup offers in comparison to the unfair offers made by ingroup members. The present findings suggest that latent intergroup biases during decision-making may be positively related to endogenous testosterone. Similar to 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 male testosterone also in other social settings.
Highlights
Humans display a large extent of prosocial behaviors such as cooperation and altruism
Post-hoc simple slope analysis of the estimated marginal means indicated that unfair offers were more likely to be rejected if they came from an outgroup proposer than from an ingroup member, only if the respondents were men with relatively high testosterone levels (t(59) = 3.64, p = 0.001)
Study 2 included a cued recall task to assess memory for previously unfair proposers of the different groups. Both studies showed a relationship between testosterone and the intergroup bias, supporting the assumption that endogenous testosterone may be related to male parochial altruism
Summary
Humans display a large extent of prosocial behaviors such as cooperation and altruism. Members of different indigenous language groups in Papua New Guinea have been shown to display a strong ingroup bias by punishing norm violators that treated members of their own group unfairly more often compared to situations, in which the ‘‘victim’’ of the unequal share was an outgroup member (Bernhard, Fischbacher & Fehr, 2006). This ingroup bias seemed to be accompanied by a stronger tendency towards outgroup hostility in contexts that involved a competition between groups. Since cooperation within the own group and successfully competing against outgroups was crucial in terms of survival, these conflicts have been proposed to have led to the evolution of both altruism and parochialism (Bowles, 2009; Choi & Bowles, 2007)
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