In humans, oxytocin promotes cognitive and motivational tendencies that benefit the groups on which humans depend for their
survival and prosperity. Here we examined decision making in an incentivized two-player poker game with either an in-group
or out-group antagonist. Sixty nine healthy males received 24 IU oxytocin or matching placebo, and played four rounds of a
simplified poker game. On each round they received either low or high value cards to create differences in competitive strength,
and then responded to a bet placed by their (simulated) (in-group or out-group) antagonist. Under placebo, participants withdrew
and competed depending on their own (low vs. high) competitive strength, regardless of their antagonist's group membership.
Under oxytocin, however, participants settled more and competed less with an in-group as compared to an out-group antagonist;
withdrawal was unaffected by group membership. We conclude that oxytocin sensitizes humans to the group membership of their
interaction partner, rendering them relatively more benevolent and less competitive towards those seen as belonging to their
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