Lucky Monroe

Congratulations! You were born a Cheater!


Ok, so, may be a bit of a conclusion jump. (I’m famous for my award winning jumps) However, I was introduced to this super cool research article that sent me down a winding wormhole of knowledge and “say what’s?”.

First, some facts. The number of Americans who actually cheat on their partners is rather substantial: Over the past two decades, the rate of infidelity has been pretty constant at around 21 percent for married men, and between 10 to 15 percent for married women, according to the General Social Survey at the University of Chicago’s independent research organization, NORC. Social messages have us thinking of sexual infidelity as a symptom of an unhappy relationship, a moral flaw or a sign of deteriorating social values. When I was trained as a psychiatrist we were told to look for various emotional and developmental factors — like a history of unstable relationships or a philandering parent — to explain infidelity. However, research is pointing in a different direction, especially for anything concerning behavior, it turns out that genes, gene expression and hormones matter a lot. A WHOLE LOT. More than we expected.

It has been accepted for a while that men have a genetic, evolutionary impulse to cheat, because that increases the odds of having more of their offspring in the world. (Because that’s just goals right? Thanks evolution!) But now there is intriguing new research showing that some women, too, are biologically inclined to wander, although not for clear evolutionary benefits. It also depends on whether or not certain variants of the vasopressin receptor gene are expressed which kind of decides if one is more likely to engage in “extra pair bonding,” the scientific euphemism for sexual infidelity. Vasopressin is a hormone that has powerful effects on social behaviors like trust, empathy and sexual bonding in humans and other animals. So mutations, which are basically nature’s game of Russian roullete, in the vasopressin receptor gene could very well alter its function, thus affecting human sexual behavior.

A study found that 9.8 percent of men and 6.4 percent of women reported that they had two or more sexual partners in the previous year. The study, which was published in the Journal of Evolution and Human Behavior, found a significant associations between five different variations of the vasopressin gene and infidelity in women only and no relationship between the oxytocin genes and sexual behavior for either sex. This is impressive and surprising because that means that about forty percent of the variation in promiscuous behavior in women could be attributed to literally just genes alone. Though a strong study and the largest of its kind, it wasn’t able to offer an explanation as to why there was no relationship between the vasopressin gene and promiscuous behavior in men. Other studies confirm that oxytocin and vasopressin are linked to partner bonding, which bears on the question of promiscuity, since emotional bonding is, in a sense, the inverse of promiscuity. Hasse Walum at the Karolinska Institute in Stockholm found that in women, but not in men, there is a significant association between one variantion of the oxytocin receptor gene and marital discord and lack of affection for one’s partner. In contrast, there was a significant correlation in men between a specific variant of the vasopressin receptor gene and lower marital quality reported by their spouses.

Now, before you run out and get your prospective partner genotyped for his or her vasopressin and oxytocin receptor genes, two caveats: Correlation is not the same as causation; there are so many unmeasured factors that contribute to infidelity. So in science, as in life, it is rare that a simple genetic variant could determine behavior.

However, certain animal studies have prompted scientists to take this data more seriously. This my dear friends is a vole.

closeup photo of tan rat
Photo by DSD on

It turns out that there are two closely related species of voles: montane voles aka the f*** boy’s of the forest, which are sexually promiscuous, and prairie voles aka the guy you meet at church, which are sexually monogamous and raise their extended families in burrows. After sex, prairie voles quickly develop a selective and enduring preference for their mate, caring for her and their young, hey, may be even throwing in foot rubs at the end of the night. Montane voles on the other hand are the guys that you get a 2 A.M “wyd” text from and are more of a one-night stand. What Dr. Insel described is that the strikingly different sexual behavior of these two species of voles reflects the action of vasopressin in their brains. The vasopressin receptors in the montane and prairie voles are in completely different brain regions so that when these receptors are stimulated by vasopressin, there are very different behavioral effects. We don’t yet know from human studies whether the vasopressin receptor genes that are linked with infidelity actually make the brain less responsive to these hormones, but given the animal data, it is plausible.

In one study of men, giving vasopressin enhanced the subjects’ memory for both happy and angry faces compared with a placebo, which implies that vasopressin could boost social affiliation and aggressive behavior since it increased social and emotional learning. These findings also suggest potential therapeutic uses for oxytocin and vasopressin for people who have either a deficit or an excess of trust and social bonding. Autism is an example of a deficit, and indeed there is preliminary evidence that oxytocin may have some beneficial prosocial effects in this disorder. In contrast, Williams syndrome is a rare genetic illness in which kids are pathologically trusting and indiscriminately befriend complete strangers. The disorder is associated with baseline oxytocin levels that are on average three times above normal, so a drug that blocks oxytocin may curb their excessive trust.

Sexual monogamy is distinctly unusual in nature: Humans are among the 3 to 5 percent of mammalian species that practice monogamy, along with the swift fox and beaver — but even in these species, infidelity has been commonly observed. The evolutionary benefit of promiscuity for men is pretty straightforward: The more sexual partners you have, the greater your potential reproductive success. But women’s reproductive capacity is more limited by biology. So what’s in it for women? There may be no clear evolutionary advantage to female infidelity, but sex has never just been about procreation. Cheating can be intensely pleasurable because, among other things, it involves novelty and a degree of sensation seeking, behaviors that activate the brain’s reward circuit. Sex, money and drugs, among other things, trigger the release of dopamine from this circuit, which conveys not just a sense of pleasure but tells your brain this is an important experience worth remembering and repeating.

So what does this all mean? Research is very far from giving us a definitive answer, however, what we do know is for some, there is little innate temptation to cheat; for others, sexual monogamy is an uphill battle against their own biology.


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