In the study, the scientists squirted oxytocin (or an inert spray) up the noses of male test subjects, some of whom were involved in a monogamous relationship with a woman and some of whom were not. Then they introduced the men to an attractive woman.
Rather than approach the attractive woman, as one might anticipate given oxytocin's reputation, the men in monogamous relationships who received oxytocin tended to keep her at a distance compared to men who received placebo squirts. Oxytocin had no effect on single guys.
In other words, giving a shot of oxytocin up the nose of bonded men tended to reinforce monogamy. This finding supports work by a Dutch scientist named Carsten de Dreu who has shown that oxytocin tends to increase trust toward members of a group, but not toward outsiders. In this case, the pretty woman is the outsider.
This is an interesting finding, but not so much because it tells us that oxytocin will forever prevent a man from stepping out. Rather, it shows us that chemicals in our heads can influence our social behavior just as they influence the behavior of animals, to the point that we do not have complete rational control over our actions.
A large body of evidence gathered over the past 15 years or so shows how chemical communication between neurons can bias our behavior. Oxytocin is only one of the chemicals involved. Stress hormones, dopamine, vasopressin, opioids (the brain's heroin) all have their say. And the science tells us that "monogamous" individuals — whether birds, rodents, or people — can be driven to have sex with those outside their socially exclusive pair bond.
One of us, Larry Young, conducts studies of bonding in a monogamous rodent called a prairie vole. His work has often been cited by social conservatives who have used the prairie vole as a kind of furry paragon of morality because the critters are stubbornly loyal to their mates. Socially, that is. Sexually, it's another story. Many bonded males are happy to have sex with another female if they happen to run across one that's in heat and willing. But they come home to their partner at end of the day.