The Brain Chemistry of Social and Sexual Monogamy

Health and medicine explained.
Nov. 27 2012 4:33 PM

The Chemistry of the Suppression of Desire

What is going on in the brain of a cheater?

Bill Clinton, Gen. David Petraeus and Arnold Schwarzenegger.
Bill Clinton, David Petraeus, and Arnold Schwarzenegger

Photographs by Mario Tama/Getty Images; Karen Bleier/AFP/Getty Images; Ben Pruchnie/Getty Images.

America does love a good sex scandal, almost as much as the British do, and the Petraeus, um, affair has been an especially juicy one. It’s been so complicated, in that reality-show kind of way, that we need charts depicting who’s connected to whom.

As always happens when a powerful married man is revealed to have been hiking the Appalachian Trail, finding Freudian uses for cigars, or supporting his maid’s child, there’s been a lot of speculation about the psychology of honcho guys. What is it about the powerful?

This noodling is off-base on several counts. First, it neglects the fact that roughly one-quarter of married people—approximately equal numbers of men and women—report having had an extramarital affair. They aren’t all powerful. It’s true that the successful may indeed be more likely to commit adultery, but not for the reasons usually cited, such as their supposed sense of entitlement.

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It also conflates social monogamy with sexual monogamy, assuming that these complicated sets of behaviors are one and the same. But Petraeus’ experience shows that’s not necessarily true. By all accounts, Petraeus highly values his relationship with his wife. Yet he was not sexually monogamous, and because he wasn’t, he placed his social relationship with his wife, not to mention his job and reputation, at risk.

The difference between social and sexual monogamy is partly chemical, as was illustrated recently in a fascinating experiment. You may have missed it while being steeped in Jill Kelley news, but the Journal of Neuroscience released a study earlier this month about the effects of the neurochemical oxytocin on the behavior of monogamous males.

Oxytocin has gotten a lot of publicity over the past few years, not all of it entirely accurate. It’s been called the “cuddle” hormone, a “love drug,” even “the moral molecule.” But it turns out that the effects of oxytocin depend on social context.

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.

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