Oxytocin, but not vasopressin, increases both parochial and universal altruism.

In today's increasingly interconnected world, deciding with whom and at what level to cooperate becomes a matter of increasing importance as societies become more globalized and large-scale cooperation becomes a viable means of addressing global issues. This tension can play out via competition between local (e.g. within a group) and global (e.g., between groups) interests. Despite research highlighting factors influencing cooperation in such multi-layered situations, their biological basis is not well understood. In a double-blind placebo controlled study, we investigated the influence of intranasally administered oxytocin and arginine vasopressin on cooperative behavior at local and global levels. We find that oxytocin causes an increase in both the willingness to cooperate and the expectation that others will cooperate at both levels. In contrast, participants receiving vasopressin did not differ from those receiving placebo in their cooperative behavior. Our results highlight the selective role of oxytocin in intergroup cooperative behavior.