Katie Daughters, Antony S.R. Manstead, Femke S. Ten Velden, Carsten K.W. De Dreu
Psychoneuroendocrinology, Available online 3 December 2016
Human groups function because members trust each other and reciprocate cooperative contributions, and reward others’ cooperation and punish their non-cooperation. Here we examined the possibility that such third-party punishment and reward of others’ trust and reciprocation is modulated by oxytocin, a neuropeptide generally involved in social bonding and in-group (but not out-group) serving behavior. Healthy males and females (N = 100) self-administered a placebo or 24 IU of oxytocin in a randomized, double-blind, between-subjects design. Participants were asked to indicate (incentivized, costly) their level of reward or punishment for in-group (outgroup) investors donating generously or fairly to in-group (outgroup) trustees, who back-transferred generously, fairly or selfishly. Punishment (reward) was higher for selfish (generous) investments and back-transfers when (i) investors were in-group rather than outgroup, and (ii) trustees were in-group rather than outgroup, especially when (iii) participants received oxytocin rather than placebo. It follows, first, that oxytocin leads individuals to ignore out-groups as long as out-group behavior is not relevant to the in-group and, second, that oxytocin contributes to creating and enforcing in-group norms of cooperation and trust.
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