Deciphering the modulatory role of oxytocin in human altruism. 
Unlike any other species, humans frequently engage in altruistic behaviors by which they increase another individual's welfare even if this implies personal costs.  The psychological motives underlying altruistic behaviors remain diverse, ranging from the ability to reciprocate trust and cooperation to bonding and empathizing with family members or even genetically unrelated others.  This article explores the neuroendocrine architecture of altruism by emphasizing the crucial role of the evolutionarily highly conserved peptide hormone oxytocin as a modulator of cooperative behaviors including empathy-driven altruism.  However, accumulating evidence suggests that oxytocin does not invariably facilitate cooperation but also produces protective or even defensive-aggressive responses in specific social contexts.  In addition, we highlight the relevance of message frames as critical determinants of whether the peptide promotes altruism toward prosocial ends.