Infidelity influenced by genes?

Human sexual behaviour is influenced by genetic, says Tim Spector, director of the Twin Research Unit at St Thomas's Hospital in London. He has found that if one of a pair of female twins has a history of infidelity, then the other is also more likely to be unfaithful to their partner. Spector says that although social factors play an important role in shaping monogamous behaviour, there is also a 'clear genetic component'.

Spector's team has been studying 3,000 pairs of twins, to look at the role of genes in disease and behaviour. According to the Sunday Times, they found that if one female twin was unfaithful, there was a 55 per cent chance that her sister would be too, compared to an estimated 23 per cent incidence of infidelity amongst women in the general population. However, Spector stressed that 'there is unlikely to be a single gene for anything like this'. Instead, he said, there are likely to be a number of genes influencing this behaviour, for example, those involved with risk-taking or other personality traits.

Spector outlined the findings in his recent book, 'Your genes unzipped'. However, a detailed account of the study will soon appear in a scientific journal, the Sunday Times reports. The newspaper quotes Spector as saying that there could be an evolutionary reason for infidelity: 'That was the technique, to produce fitter, better children rather than staying with an original partner if a better one comes along'.

Social psychologist Petra Boynton disagrees with Spector's conclusions. She told BBC News online that if children see their mother cheat on their father, they might copy the behaviour. 'It is not predisposed by genes, it's because you think that is what a relationship is like or that you can get away with it', she said. However, twin studies are designed to tease apart the influence of social and genetic factors, since they compare non-identical twins - who share their environment but only half their genes - with identical twins, who share both their environment and all their genes.

Spector apparently found that identical twins are more likely to share sexual behaviour patterns than non-identical twins, which suggests that there could be a genetic component to the trait.