Does cheating run in families? Is infidelity, in fact, genetic? A recent study of 7,378 Finnish people between the ages of 18 and 49 uncovered a genetic component to bed-hopping. Surprisingly, the researchers found a link between specific mutations of a receptor gene for vasopressin and infidelity in women... but not men.

Vasopressin is a hormone that is synthesized in the hypothalamus and stored in the posterior pituitary. From there, the hormone is secreted into the bloodstream; however, some of the hormone may release directly into the brain. Recent research suggests vasopressin impacts our trust and empathy levels, playing an important role in bonding, social behavior, and sexual motivation.

Interestingly, it has a very brief half-life — just 16 to 24 minutes.

Mutations in a receptor gene might alter its function and so affect behavior normally modulated by its matching hormone. Based on this theory, a research group led by Dr. Brendan P. Zietsch, a psychologist at Australia’s University of Queensland, explored whether some people might be inclined to be unfaithful due to some variation in their vasopressin and oxytocin receptor genes.

Bed of Choice

To begin, the team used data from an extensive study of Finnish twins and their siblings, winnowing the field of participants down to a subset of 7,378 people who had been in a relationship during (at least) the last year. Of these people, 9.8 percent of the men and 6.4 percent of the women reported having had two or more sexual partners over the previous year. After collecting saliva samples and sequencing genomes, the scientists analyzed all the data.

A significant relationship was found between five separate variants of the vasopressin gene and infidelity in women. Strangely, the same link did not exist for men; and nothing connected the oxytocin genes to the sexual behavior of either sex.

A companion to vasopressin, oxytocin, the so-called love hormone, is released whenever we hug or kiss another person, while giving birth or breastfeeding, and during sex.

Because the study involved twins and siblings, the researchers further analyzed the impact of genetic and environmental factors. Brother-sister sibling pairs were not found to be similarly unfaithful. Genes, the researchers concluded, accounted for about 63 percent of the variation in faithless behavior in men and 40 percent in women.

“We found significant genetic influences accounting for around half the variation in extrapair mating in both sexes, confirming biological underpinnings to the behavior,” concluded the researchers.

Despite causing pulses to race, the researchers warn their findings are inconclusive and require more research. A similarly inconclusive yet also surprising study examined what most people believe to be a more likely cause of infidelity: money.

The Medium Bucks

Anecdotally, it would seem, high-earning men are more likely to cheat than average-income men. But is this true?

A few years back, Christin Munsch, then a sociology doctoral student at Cornell University, looked at income levels and their potential impact on marital fidelity. Her study included young couples only, yet what she found amounts to disturbing news for women: While dependence breeds fidelity in women, the opposite is true for men.

Stay-at-home dads and other men who are completely dependent on their wives’ income are a whopping five times more likely to cheat than men who contribute an equal amount of money to the shared kitty. At the same time, men earning significantly more than their partners also are more likely to stray from the marriage bed.

Munsch says the number of people who cheat — or admit to it — is (happily) very small. She also suggests that a more generalized unhappiness may be the reason why a dependent man strays from his wife. Still, it appears the middle ground of financial equality (or near equality) works best for many couples.

Source: Zietsch BP, Westberg L, Santtila P, Jern P. Genetic analysis of human extrapair mating: heritability, between-sex correlation, and receptor genes for vasopressin and oxytocin. Evolution and Human Behavior. 2014.