And discrimination is part of that.
Oxytocin is a neurotransmitter "intricately involved in social behaviors such as mother-child bonding, feelings of trust and love, and group recognition," according to Social psychologist Dr. Carsten De Dreu of the University of Amsterdam.
A study conducted by Dr. De Dreu and recently published in Proceedings of the National Academy of Sciences documents a connection between Oxytocin and racial discrimination. “Under oxytocin we saw an increase of in-group favoritism, which has the downside of discrimination against people who are not part of your group,” says Dr. De Dreu.
In all of the experiments, men who snorted a dose of oxytocin showed stronger and more frequent favoritism towards their countrymen over rival groups. Men who whiffed a placebo still showed signs of favoritism, but less frequently and at weaker levels. [Dave Mosher, "'Cuddle Chemical' Also Fuels Favoritism, Bigotry," Wired, 12 January 2011]
Dr. De Dreu acknowledges the survival value of such discrimination: "We thought it was odd a neurological system that survived evolution would make people indiscriminately loving toward others.”