A new study shows that a man’s genes can affect his bonding behaviors—namely, his ability to be monogamous and faithful in his marriage. Researchers at the Karolinska Institute in Sweden, who studied more than 1,000 heterosexual couples, found that a variant of a gene (called an allele) is linked to whether a man will be monogamous, how a woman will judge his emotional state, and whether he'll get married or simply live with his partner. About 40 percent of men have one or two copies of this allele.
According to the study, led by postgraduate student Hasse Walum, men with two alleles are more likely to have problems in their marriage than are men with one allele, and men with one allele are more likely to have marital discord than men who don’t have any copies of the allele. About 15 percent of men without the allele said they had a serious crisis in their relationship within the last year, while 34 percent of men with two copies of the allele said they faced such problems. Women married to men who had one or no copies of the allele were more satisfied with their marriages than were women married to men with two alleles. And when it came to getting married in the first place, 17 percent of men without the allele were living with women they weren’t married to, while 32 of percent of men with two alleles were living unmarried with their partners.
The inspiration for the study, published in the Proceedings of the National Academy of Sciences, came from earlier research on pair bonds in voles. This research found that high levels of the hormone vasopressin were present in the brains of males who remained monogamous and stayed with their mates to raise children. The finding led scientists to a gene that influences the activity of vasopressin and its brain receptors. Researchers theorize that because males with the variant gene are less susceptible to the positive feelings caused by the hormone (which are similar to the effects of oxytocin), they are less likely to seek long-term commitment.
Many scientists, however, are quick to note that the gene is only one of many factors (including love, loyalty, family background, and religion) that determine marital fidelity and the genetic variation is no guarantee of a bad marriage. "There are, of course, many reasons why a person might have relationship problems," Walum said in a press release, "but this is the first time that a specific gene variant has been associated with how men bond to their partners." Still, he says, the affect of the variation is "modest" and the gene should not be seen as an accurate predictor of a man's faithfulness or how he'll act in a future relationship. —Stephen Mapes