Study: Men With Genetic Variant Struggle With Commitment
JOHN TIMMER - Ars Technica


While many humans at least aspire to monogamous relationships, pairing among our animal colleagues can range from complete monogamy to an "anything goes" approach to sexual commitment. In at least one cluster of closely related species, differences in pair-bonding behavior have been tied to a genetic difference that affects a receptor for a hormone called arginine vasopressin (AVP). Now, researchers have used a panel of twins to study the same gene in humans, and they find results suggesting it may influence relationship behavior as well.

The new research is built on past studies of behavior in a set of related species of rodents. In the prairie vole, males are largely monogamous and display pair-bonding behavior. In the montane and meadow voles, polygamy is typical. Researchers have found that this behavioral difference largely boils down to a genetic difference near the receptor for AVP; the hormone's significance was confirmed by injections of AVP antagonists, which disrupted the pair bonding behavior.

Human social interactions are obviously quite a bit more complex than those displayed by voles, so it wasn't clear that the importance of the AVP receptor would be retained in people. Nevertheless, the authors of the new study, which will appear later this week in the Proceedings of the National Academies of Science, provide several reasons to think that it might. The DNA near the gene for the receptor, AVPR1A, is the site of several genetic differences, and these have been tied to aspects of social behavior, including altruistic behavior and autism spectrum disorders.

The authors used a panel of over 1,000 twins from a Swedish population that were involved in relationships of over five years, 82 percent of whom were married. The twins and their partners were surveyed for relationship behavior and their genotype at several sites near AVPR1A was determined. Correlations between the relationship scores and genotypes were determined.

The prairie vole

A single variant, termed RS3, showed a statistically significant connection with behavior within a relationship, leading the authors to focus on a comparison between males carrying two copies of a specific genetic variant called 334 and those with no copies. Those with two copies of RS3-334 were nearly twice as likely to be in unmarried relationships (32 vs. 17 percent), and over twice as likely to report what they termed a "marital crisis" within the last year (34 vs. 15 percent). Their partners also rated their relationships lower in the areas of affection expression, cohesion, and consensus.

One note of caution is that the absolute number of people falling into each genotype were not clearly described here; although the results are reported as statistically significant, it would be reassuring to know precisely what the population size is.

The authors note that genetic differences in AVPR1A have been associated with a variety of social interactions, and that their data indicates that behavior within a relationship is simply one of these; this is not simply a "monogamy gene," as the story is being reported. Still, they suggest that its effect on relationships may be more dramatic than this initial study indicates, as they biased their population by selecting for people in long-term relationships. Expanding the study to those not in relationships may reveal an even stronger effect.