September 4, 2008 Comedian Robin Williams once defined the key issue of fidelity as being that men had a brain and a penis and only enough blood to run one at a time. We all know some guys are faithful, and some are not, but until now, it all appeared random behaviour. Now new research suggests that men who carry a certain gene behave differently in relationship. The incidence of the gene has been statistically linked to the incidence of a marital or relational crisis in the past year ,how strongly the man felt he had bonded with his partner, and what their respective partners thought about their relationship. One wonders if perhaps one day we’ll see genetic screening for prospective partners?

Scientists at Karolinska Institutet have found a link between a specific gene and the way men bond to their partners. The results, which are presented in the scientific journal PNAS, can lead to a better understanding of such problems as autism and social phobia.

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"There are, of course, many reasons why a person might have relationship problems, but this is the first time that a specific gene variant has been associated with how men bond to their partners," says Hasse Walum, postgraduate student at the Department of Medical Epidemiology and Biostatistics.

He stresses, however, that the effect of this genetic variation is relatively modest, and it cannot be used to predict with any real accuracy how someone will behave in a future relationship.

Hasse Walum and his colleagues made use of data from The Twin and Offspring Study in Sweden , which includes over 550 twins and their partners or spouses. The gene under study codes for one of the receptors for vasopressin, a hormone found in the brains of most mammals. The team found that men who carry one or two copies of a variant of the gene allele 334 often behave differently in relationships than men who lack this gene variant.

The incidence of allele 334 was statistically linked to how strong a bond a man felt he had with his partner. Men who had two copies of allele 334 were also twice as likely to have had a marital or relational crisis in the past year than those who lacked the gene variant. There was also a correlation between the men’s gene variant and what their respective partners thought about their relationship.

"Women married to men who carry one or two copies of allele 334 were, on average, less satisfied with their relationship than women married to men who didn t carry this allele", says Hasse Walum.

The same gene has been previously studied in voles, where it has been linked to monogamous behaviour in males.

"The fact that the corresponding gene has proved important for similar behaviour in voles makes our findings even more interesting, and suggests that the thoroughly studied brain mechanisms that we know give rise to strong bonds between individual voles can also be relevant to humans", Hasse Walum concludes.

The team hopes that greater knowledge of the effect of vasopressin on human relations will one day give science a better understanding of the causes of diseases characterised by problems with social interaction, such as autism.