UNFAITHFUL women have a new excuse — their misbehaviour might be down to their genes. A scientific study has shown that a woman’s tendency to be unfaithful could be linked to particular genes inherited from her parents.

The study suggests that about a quarter of British women carry the infidelity trait and that it sharply increases the chances that they will sleep with someone else while in an apparently monogamous relationship with a man.

While the genetic element is far from exclusively responsible for infidelity — the state of a relationship and cultural factors are key elements — it sharply raises the chances that a woman will sleep with someone while she is in an apparently monogamous relationship with a regular partner.

The gene findings have emerged from comparing a study of 5,000 female twins with a survey of 5,000 unrelated women. The work, carried out by researchers at Guy’s and St Thomas’ hospital, London, and part-funded by the Medical Research Council, was led by Tim Spector, professor of genetic epidemiology at St Thomas’.

Spector has written a scientific paper on his findings and submitted it to academic journals. He has also outlined them in a newly published book, Your Genes Unzipped, which describes how people’s behaviour and lives are affected by genetic factors.

“By studying twins, we can separate nature from nurture,” Spector said. “It does seem that there is a strong link between a woman’s genetic inheritance and the chances that she will commit infidelity.”

Parental inheritance might explain the infidelities that have both plagued and blessed families such as the Redgrave acting dynasty.

Sir Michael Redgrave, the founder, was a bisexual whose dalliances included Edith Evans and Noël Coward. Vanessa Redgrave divorced Tony Richardson, the film director, because of his affair with Jeanne Moreau, the French actress.

One of the couple’s daughters, Natasha Richardson, started her romance with Liam Neeson, now her husband, while she was still married to Robert Fox, the theatre producer.

The couple’s other daughter, Joely Richardson, had an affair with Archie Stirling, husband of Dame Diana Rigg, who was almost 30 years older than her.

The idea that genes can influence behaviour as well as physical appearance and health is one of the most controversial and fastest-growing areas of modern genetic research.

The controversy arises from the idea that people’s freedom of choice might be heavily influenced by their DNA.

Spector’s findings will be seen as highly sensitive by scientific publishers who remember the angry public debate when researchers suggested in 1993 that homosexuality had a largely genetic basis.

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