Genes keep your jeans on

If your man has a wandering eye, the reason is just what you always suspected - the problem's in his genes.

Scientists believe they have located part of the DNA that governs faithfulness. They transplanted it from monogamous prairie voles to their promiscuous cousins, meadow voles.

The latter group promptly gave up nest-hopping and became doting partners. It is thought the same gene exists in humans and, as well as being involved in romantic relationships, could hold the key to drug addiction and disorders such as autism.

Dr Larry Young, from Emory University School of Medicine in Atlanta, Georgia, said: 'Our study provides evidence, in a comparatively simple animal model, that changes in the activity of a single gene can change profoundly a fundamental social behaviour of animals within a species.'

The love gene controls the strength of a brain hormone called vasopressin, according to Nature journal.

Varying levels of the chemical are thought to explain the contrasting mating behaviour of the two breeds of vole.

Rampant meadow voles are believed to lack vasopressin receptors in a 'reward centre' of the brain that helps create the experience of pleasure.

The researchers pointed out that many genes are probably involved in regulating lifelong bonds between humans.

But Dr Young said: 'It is intriguing to consider that individual differences in vasopressin receptors might play a role in how differently people form relationships.'

Previous human studies have shown that similar pathways in the brain are involved in drug addiction.

Dr Miranda Lim, a member of the Emory team, said: 'The brain process of bonding with one's partner may be similar to becoming addicted to drugs. Both activate reward circuits in the brain.'