Oxytocin promotes synchronized out-group attack during intergroup conflict in humans
Intergroup conflict contributes to human discrimination and violence, but persists because individuals make costly contributions to their groups fighting capacity. Yet how groups effectively synchronize their contributions during intergroup conflict remains poorly understood. Here we examine whether the evolutionary ancient neuropeptide oxytocin provides a neurobiological mechanism underlying group synchronization to attack or defend during real-time intergroup conflict. In a double-blind placebo-controlled study with N=480 males in Attacker-Defender intergroup conflicts, we found that oxytocin reduced attackers contributions and over time increased attackers within-group synchronization of contributions. However, rather than becoming peaceful, oxytocin enabled attackers to track rivals defense-history and synchronize their contributions into well-timed (when defenders were weak) and hence more profitable attacks. Combined, results reveal behavioral synchronization and coordinated action as critical components of successful attacks, subscribe to the possibility that oxytocin enables individuals to contribute to in-group efficiency and prosperity, even when such implies outsiders are excluded or harmed.