Men who are lacking in the romance department may have a new excuse to offer their wives or significant others: They can blame it on their DNA.
A new study in the Proceedings of the National Academy of Sciences suggests that a certain gene variant found in some men is linked to less bonding and more trouble in a long-term relationship.
The story of this gene starts not with men, but with prairie voles — small, furry rodents that have underground burrows. Prairie voles stay with one mate to raise their little ones. That's intriguing, because other species of voles don't do that.
A few years ago, biologist Larry Young at Emory University showed that the special bonding behavior of male prairie voles seemed to be linked to a single gene, which is associated with a brain hormone called vasopressin.
"We were actually able to take the gene from the prairie vole and inject it into the brain of the meadow vole, which normally should not form bonds," Young says. "And when we did that, the meadow voles were actually able to form an attachment to their mate."
Reporters quickly dubbed this "the monogamy gene" and speculated that a similar gene might affect the ability of human males to commit to a partner.
"It certainly got a lot of attention," says Young, "and usually every Valentine's Day, we get lots of calls."
Hasse Walum, a researcher at the Karolinska Institute in Sweden, decided to study this gene in men.
"What we wanted to do was to see if variation in the same gene was associated with variation in how humans bond with their partners," Walum said.
Walum and his colleagues had DNA samples from hundreds of men who were participating in a study of twins. The men had also answered questions about their relationships with their spouses or significant others. "Questions like, 'How often do you kiss your partner?' and things like that," Walum explains.
The researchers say that men who had a certain variant of the gene didn't score as high on these measures of bonding.
Although only 15 percent of the men without this gene variant reported that they had had a marital crisis or a threat of divorce in the past year, 34 percent of the men with two copies of the gene variant said that they had experienced a crisis.
Young says other scientists need to confirm the finding to make sure it's real.
"But if it is true," says Young, "it's very intriguing that the same gene that is involved in pair bonding in a little rodent could be affecting our own relationships."
Still, don't expect brides to demand pre-marital gene tests of their grooms anytime soon. Erik Parens, a bioethicist at The Hastings Center in New York, urges caution.
He says the study may show that, as a group, men with this gene variant seem more likely to have trouble bonding, at least on this test. But that doesn't mean a gene test could make an accurate prediction for any individual man.
Even in this study, Parens points out, "it's possible to have the gene variant, but to not have the marital difficulties. And it's also possible to have the marital difficulties, and to not have the gene variant."
Plus, he adds, human relationships are so complicated that the effect of any one gene would be very small.