Richard Friedman in The New York Times:
AMERICANS disapprove of marital infidelity. Ninety-one percent of them find it morally wrong, more than the number that reject polygamy, human cloning or suicide, according to a 2013 Gallup poll. Yet 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. We are accustomed to 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. But during my career, many of the questions we asked patients were found to be insufficient because for so much behavior, it turns out that genes, gene expression and hormones matter a lot. Now that even appears to be the case for infidelity.
We have long known that men have a genetic, evolutionary impulse to cheat, because that increases the odds of having more of their offspring in the world. But now there is intriguing new research showing that some women, too, are biologically inclined to wander, although not for clear evolutionary benefits. Women who carry certain variants of the vasopressin receptor gene are much more likely to engage in “extra pair bonding,” the scientific euphemism for sexual infidelity.