Gene May be Responsible for Lack of Commitment

Scientists have discovered a gene variation that may make it difficult for some men to stay monogamous. The study, to appear in the Proceedings of the National Academy of Science, is the first to examine whether a hormone that encourages monogamy in animals has the same effect on humans.

The study focused on a gene that codes for the vasopressin hormone in the brain. Vasopressin has many functions in the body, such as helping to keep a regular balance of salts in the blood and to control the amount and frequency of urination. Scientists have long studied how vasopressin influences behavior in prairie voles, a mouselike animal that is known for monogamy. Through a series of studies that manipulated vasopressin levels in the vole brain, scientists have been able to make the animals more, or less, faithful.

The new study on humans examined a gene that codes for a vasopressin receptor in the human brain. Walum and colleagues had 500 couples fill out questionnaires to measure their level of “pair bonding” and marital strife. The couples, whom had been together for at least five years, were asked questions such as “How often do you kiss your mate?” and, “Have you discussed divorce or separation with a close friend?”

Researchers found that a variation of the gene, called allele 334, was associated with lower scores on partner bonding and greater odds of marital conflict. The effect was more prominent in men. Of men with no copies or just one copy of the 334 allele, 15 to 16 percent reported a marital crisis in the past year. However, of the men with two copies of the 334 allele, the odds of marital crisis was 34 percent.

This is one of the few studies that has focused on a single gene and found a large effect on behavior. Even if the results are replicated in further studies, however, it is important to remember that humans are complex, and many variables come into play in a relationship. Genes are only one factor in behavior.

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