Why do we cheat? Only about 3% of mammals on Earth are monogamous, and humans are among them. The evolutionary and economic benefits of monogamy are hard-wired into us so strongly that monogamy is a sociocultural norm as well…and its opposite, scientifically known as “extrapair bonding” and colloquially known as cheating, is highly frowned upon. More Americans condemn cheating than suicide, human cloning or even polygamy, about 91% according to a 2013 Gallup poll.
So is there a science behind cheating? Can cheating…er, extrapair mating…be explained by any kind of experimental models? Advancements in genetic and hormone studies have shown that, well, yes, there is…sort of.
Dopamine is a powerful hormone secreted by the human brain in response to positive stimulation: a feel-good hormone, if you will. One study has shown that a specific variant of dopamine receptors translates to a greater propensity for extrapair mating. In 2010, Dr. Justin Garcia surveyed 181 adults and demonstrated, using his findings, that individuals with a specific variant of dopamine receptors were 50% likely to cheat, while those who didn’t have that specific variant were only about 22% likely to cheat. Those reporting a higher likelihood of extrapair mating also reported a greater likelihood to take risks, and a greater propensity for addiction, substance abuse and alcoholism.
Furthermore, studies on the hormone vasopressin have indicated that genetics play a greater role in extrapair mating tendencies than previously thought. Men with lower levels of vasopressin, a hormone similar to oxytocin, are more likely to cheat on their mates, while men with higher levels are less likely to. Studies have shown the effects of vasopressin on other species as well: in a study where mondane voles, a sexually promiscuous species, were injected with vasopressin, they became monogamous. Studies in human males who have been injected with vasopressin show increases in pair bonding as well as other monogamous traits. Vasopressin functions, it appears, in men almost exactly as oxytocin does in women (oxytocin in women is responsible for nesting and mating tendencies, establishment of bonds with children, and similar attributes), though more studies must be conducted to prove this conclusively.
Some studies have shown some economic factors weigh heavily into the extarpair mating game: specifically, who makes more money in the relationship. Men who earn significantly less than their mates are about twice as likely as women in the same earning scenario. The percentage of cheaters is still pretty small, though: 7% of men within the study, compared to 3% of women.
Other social factors do certainly weigh in: happiness with one’s relationship, availability of extrapair mates, age, cultural acceptance, the list goes on ad infinitum. But knowing that there may be a genetic component to cheating might make it easier to accept for the person who was at the other end of the cheating…though it also might take away any plausible deniability to the oft-spoken phrase “once a cheater, always a cheater”.