The secret of love: promiscuous voles point to a gene for monogamy

For centuries, the difference between a bed-hopping Casanova and a dull but devoted spouse has been considered a matter of moral choice.

For centuries, the difference between a bed-hopping Casanova and a dull but devoted spouse has been considered a matter of moral choice.

Not any more. Researchers have found that red-blooded Lotharios and lovers of pipes and slippers could be distinguished by a single gene.

A team from the Emory University School of Medicine in Atlanta, Georgia, isolated a gene present in the prairie vole, a species known for its loyalty to a single partner, and injected it into their notoriously promiscuous cousin, the meadow vole. The result was that the meadow voles switched their amorous instincts from nest hopping to steadfast monogamy. The researchers believe the same gene exists in humans as part of the genetic chain that regulates lifelong bonds.

The role of the "love gene" is linked to a hormone in the brain, called vasopressin, which controls the sense of pleasure.

The gene stimulates production of a receptor protein which, in turn, regulates the effect of the hormone. Scientists believe the promiscuous meadow voles lack these vasopressin receptors. Larry Young, who led the team, said: "Our study provides evidence, in a comparatively simple animal model, that changes in the activity of a single gene can change a fundamental social behaviour of animals within species. It is intriguing to consider that individual differences in vasopressin receptors in humans might play a role in how different people form relationships."

The scientists, whose research is published today in Nature, believe that the gene's role may extend far beyond romantic behaviour to areas such as drug addiction and even autism, where people have difficulties forming social bonds.

They warned the effect of a single gene should not be exaggerated in controlling complex social interactions, saying it formed part of a social and biological network which determine human relationships. But previous studies linked to vasopressin have shown that similar pathways in the brain are also involved in drug addiction, raising the prospect that love may indeed be a drug.

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