If you knew that your husband was twice as likely to be unfaithful in your marriage than another man, would you still marry him? Scientists have discovered a gene that may be able to tell just that. The question is: would you want to know if he had the gene?

We know strong emotional relationships are essential to mental health. We do not know, however, how the brain functions in establishing and maintaining such complex interactions.

Scientists have examined the formation and regulation of complex social behaviors in non-human mammals for decades, finding that the hormones oxytocin and vasopressin are among the key modulators in such connections. One such study compared prairie voles and montane voles. Prairie voles mate for life and raise litters of offspring together. In contrast, montane voles do not form lasting pair-bonds and the males are not involved in raising offspring. In the prairie vole males, bonding triggers vasopressin action in the reward centers of the brain, prompting the animals to seek monogamous relationships. Montane voles have less vasopressin activity, which predicts the lack of life-long bonding.

Another study of rats concluded that vasopressin acts not just in pair-bonding behaviors, but facilitates anxiety and aggression in males. Oxytocin was found to be the key mediator for female social behaviors and maternal attachments.

Similarly, in humans, vasopressin is more active in males and is associated with social behaviors including aggression, pair-bond formation, and anxiety. Oxytocin is more abundant in woman, involved in reducing behavioral responses to stress and inhibiting defensive behavior. However, both hormones act in both males and females to regulate complex social behaviors, including human attachment and social recognition.

A recent study published in the Proceedings of the National Academy of Sciences reported an association of human gene variants controlling vasopressin activity in males and pair-bonding behavior. The variant allele is present in 2 of every 5 men and predicts partner bonding, marital problems, marital status, and marital quality. Men with 2 copies of the variant allele are twice as likely to experience marital problems, including divorce, separation, and infidelity, compared to men with one or no copies of the allele.

The scientists at the Karolinska Institute in Stockholm studied vasopressin activity and gene variation in 1000 heterosexual couples. Approximately 40% of the men had 1 or 2 copies of the genetic variation. While men with 2 copies of the gene were at the highest risk for marital discord, men with 1 copy were at higher risk than those with no copies of the variant. Only 15% of the men with no variant alleles reported marital problems, while 34% of men with 2 copies of the variant reported marital problems. Additionally, 17% of the men without the allele lived with women without being married, while 32% of men with 2 variant alleles lived with women without being married.

Further, women married to men with 2 variant alleles reported lower marital satisfaction than women married to men with one or no copies. Marital satisfaction was based on affection, cohesion, and consensus in the relationship described by the wives and partners of the men.

While more work is needed to replicate and confirm these findings, scientists do agree that vasopressin can change how men behave in social relationships. Building on this study, many researchers believe that vasopressin may act in other dysfunctions of social behavior including autism, obsessive-compulsive disorder, and borderline personality disorder. New research may provide potential therapeutic targets for these psychiatric disorders.

A gene alone cannot accurately predict whether a man will make a happy and faithful husband — and many people overcome genetic predispositions for behaviors and conditions — but this discovery is evidence that genes work with our environment, culture, and experience to shape who we are and who we might become.

References

M LIM, L YOUNG (2006). Neuropeptidergic regulation of affiliative behavior and social bonding in animals Hormones and Behavior, 50 (4), 506-517 DOI: 10.1016/j.yhbeh.2006.06.028

H. Walum, L. Westberg, S. Henningsson, J. M. Neiderhiser, D. Reiss, W. Igl, J. M. Ganiban, E. L. Spotts, N. L. Pedersen, E. Eriksson, P. Lichtenstein (2008). Genetic variation in the vasopressin receptor 1a gene (AVPR1A) associates with pair-bonding behavior in humans Proceedings of the National Academy of Sciences, 105 (37), 14153-14156 DOI: 10.1073/pnas.0803081105

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