Opposing effects of oxytocin on moral judgment in males and females.

Current perspectives on the evolutionary roots of human morality suggest it arose to incentivize social cooperation by promoting feelings of disgust toward selfish behavior, although the underlying neural mechanisms remain unclear. To investigate whether the ancient mammalian neuropeptide oxytocin (OXT) influences self-referential processing in the domains of emotion evaluation and moral decision making, we conducted a pharmaco-functional magnetic resonance imaging (fMRI) and a behavioral experiment involving 157 healthy women and men who were treated with either OXT (24 IU) or placebo (PLC) intranasally. Our results show that OXT facilitated cortical midline responses during self-processing of disgust and selectively promoted self-interest moral judgments in men. In contrast, in women OXT increased the reaction time difference between accepted and rejected moral dilemmas and led them to suppress their self-interest and respond more altruistically for the benefit of others. Taken together, these findings suggest an OXT-related sexual dimorphism in human moral behavior which evolved adaptively to optimize both protection and nurturing of offspring by promoting selfish behavior in men and altruistic behavior in women.