Oxytocin is a naturally occuring hormone that has long been associated with pregnancy and breast feeding in women. Scientists suspected that it may have a role in the bonding that occurs between a mother and her new born child, and this – as well as a wider role in social bonding in general – was first confirmed in a 2003 study1 involving prairie voles. The levels of oxytocin in these famously monogamous mammals was found to increase in the brain of the female vole during sex with its partner.
Since that noted study, countless other research teams have explored and confirmed further the role of oxytocin in bonding, empathy, trust, and even sexual attraction. These findings, often reported in the mainstream media and press, have given oxytocin the popular tage of the ‘love hormone’, the ‘cuddle hormone’, or the ‘trust hormone’. But to complicate matters, several studies appear to have suggested that the love hormone may have a darker side – among other things, possibly reinforcing ingroup and outgroup preferences, potentially being a cause of racism.
 Vacek, Marla (2002). “High on Fidelity: What can voles teach us about monogamy?”. American Scientist.