Oxytocin

Oxytocin is a powerful hormone and acts as a neurotransmitter in the brain. It regulates social interaction and sexual reproduction, playing in role in behaviors from maternal-infant bonding and milk release to empathy, generosity, and orgasm. When we hug or kiss a loved one, oxytocin levels increase; hence, oxytocin is often called "the love hormone." In fact, the hormone plays a huge role in all pair bonding. The hormone is greatly stimulated during sex, birth, and breastfeeding. Oxytocin is the hormone that underlies trust. It is also an antidote to depressive feelings.

For all its positivity, however, oxytocin has a dark side. Or, more accurately, it plays a more complex role in human behavior than is commonly thought. As a facilitator of bonding among those who share similar characteristics, the hormone fosters distinctions between in-group and out-group members, and sets in motion favoritism toward in-group members and prejudice against those in out-groups. Ongoing research on the hormone is a potent reminder of the complexity of biological and psychological systems.