Abstract
Parochial altruism, defined as increased ingroup favoritism and heightened outgroup hostility, is a widespread feature of human societies that affects altruistic cooperation and punishment behavior, particularly in intergroup conflicts. Humans tend to protect fellow group members and fight against outsiders, even at substantial costs for themselves. Testosterone modulates responses to competition and social threat, but its exact role in the context of parochial altruism remains controversial. Here, we investigated how testosterone influences altruistic punishment tendencies in the presence of an intergroup competition. Fifty male soccer fans played an ultimatum game (UG), in which they faced anonymous proposers that could either be a fan of the same soccer team (ingroup) or were fans of other teams (outgroups) that differed in the degree of social distance and enmity to the ingroup. The UG was played in two contexts with varying degrees of intergroup rivalry. Our data show that unfair offers were rejected more frequently than fair proposals and the frequency of altruistic punishment increased with increasing social distance to the outgroups. Adding an intergroup competition led to a further escalation of outgroup hostility and reduced punishment of unfair ingroup members. High testosterone levels were associated with a relatively increased ingroup favoritism and also a change towards enhanced outgroup hostility in the intergroup competition. High testosterone concentrations further predicted increased proposer generosity in interactions with the ingroup. Altogether, a significant relation between testosterone and parochial altruism could be demonstrated, but only in the presence of an intergroup competition. In human males, testosterone may promote group coherence in the face of external threat, even against the urge to selfishly maximize personal reward. In that way, our observation refutes the view that testosterone generally promotes antisocial behaviors and aggressive responses, but underlines its rather specific role in the fine-tuning of male social cognition.
Highlights
The propensity to help and benefit fellow group members, even when incurring costs for oneself, and an increased hostility towards ‘‘outsiders’’ that are not part of one’s own group are behaviors commonly observed in humans [1]
The aim of the present study was to assess whether endogenous testosterone shapes parochial altruism in human males, and, to examine how testosterone influences altruistic behavior during an intergroup conflict
Two major findings emerged: Firstly, subjects with high testosterone levels exhibited a change towards increased outgroup hostility during the intergroup competition, whereas those with low testosterone concentrations acted rather selfishly in the competitive setting (Fig. 4)
Summary
The propensity to help and benefit fellow group members, even when incurring costs for oneself (altruism), and an increased hostility towards ‘‘outsiders’’ that are not part of one’s own group (parochialism) are behaviors commonly observed in humans [1]. Humans tend to altruistically punish free-riders who commit social norm violations and reward norm-abiding acts even at substantial costs for themselves [2,3] They typically favor genetically unrelated group members (e.g., people from the same linguistic group) over those from a distant outgroup and show increased hostility as well as reduced empathy and trust towards outsiders (e.g., [4,5,6,7]). If groups frequently compete over resources or territory, group success often depends on the willingness of individuals to altruistically engage in hostile acts with outsiders, even at risk of high personal costs like death or mutilation [1] In this context antisocial acts of aggression or non-cooperation that damage outgroup members do protect and support the prosperity of the ingroup and indirectly strengthen internal cooperation. Parochial altruism may paradoxically promote both ingroup cooperation and outgroup hostility, which contribute to group success in intergroup conflicts and probably encouraged the proliferation of these expensive group-beneficial behaviors in humans [9]
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