Abstract
Intergroup conflict is often driven by an individual's motivation to protect oneself and fellow group members against the threat of out-group aggression, including the tendency to pre-empt out-group threat through a competitive approach. Here we link such defense-motivated competition to oxytocin, a hypothalamic neuropeptide involved in reproduction and social bonding. An intergroup conflict game was developed to disentangle whether oxytocin motivates competitive approach to protect (i) immediate self-interest, (ii) vulnerable in-group members, or (iii) both. Males self-administered oxytocin or placebo (double-blind placebo-controlled) and made decisions with financial consequences to themselves, their fellow in-group members, and a competing out-group. Game payoffs were manipulated between-subjects so that non-cooperation by the out-group had high vs. low impact on personal payoff (personal vulnerability), and high vs. low impact on payoff to fellow in-group members (in-group vulnerability). When personal vulnerability was high, non-cooperation was unaffected by treatment and in-group vulnerability. When personal vulnerability was low, however, in-group vulnerability motivated non-cooperation but only when males received oxytocin. Oxytocin fuels a defense-motivated competitive approach to protect vulnerable group members, even when personal fate is not at stake.
Highlights
Intergroup relations are often marked by non-cooperation and competitive behavior, creating levels of aggression and violence that bring about severe societal costs [1,2,3]
As predicted in hypothesis (i), in-group tending was higher when participants received oxytocin rather than placebo, M = 3.828 vs. M = 3.002, F(1,94) = 7.23, p = 0.008, partial g2 = 0.071 In-group defending was measured in 72 participants (Methods & Materials), and was predicted by a significant Treatment6In-Group Vulnerability interaction, F(1,64) = 7.18, p,0.010, partial g2 = 0.093
Through a newly developed inter-group game we clarified that earlier findings should not be interpreted as if oxytocin increases the individual’s motivation to serve personal interests
Summary
Intergroup relations are often marked by non-cooperation and competitive behavior, creating levels of aggression and violence that bring about severe societal costs [1,2,3]. Defense-motivated non-cooperation serves group-interests because it may pre-empt possible attack by rivaling out-groups and may deter them from aggressing against the ingroup [7,12]. Group-living animals such as Siberian Jays and Meerkats aggress against rivals and predators especially in the presence of offspring, and such parental mobbing increases offspring survival and provides for group formation and cooperative kin-societies [13,14,15]. In humans, such parochial altruism has likewise been associated with group survival and prosperity [4,11]
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