It sounds like the perfect excuse for a wandering eye -- a man's tendency to be unfaithful may be influenced by his genes, research suggests.

Men who inherit a genetic variant that affects an important attachment hormone are more likely than usual to have weaker relationships and marital problems, and less likely to be married, according to the research. Their wives and girlfriends are also more likely to be less satisfied with them as partners.

While the study did not look directly at infidelity, the findings suggest that male monogamy might also be influenced by variations in a single gene. The study's authors cautioned that any effect would apply only on average, and that it was impossible to predict whether any individual would be unfaithful or a bad partner on the basis of his genes.

The gene in question affects the receptor for a hormone called vasopressin, which plays an important role in social behaviour, pair-bonding and sexual attachment. Its effects were first characterised by studies of different species of voles. Although the meadow and prairie voles are close cousins, their sexual behaviour is dramatically different.