Genes play an important role in determining whether women cheat on their sexual partners, according to one of the largest studies of sexual behaviour undertaken in Britain. About 40 per cent of infidelity is genetic and the remainder comes from upbringing and other environmental factors.

The Twin Research Unit at St Thomas's Hospital, London, carried out the study with 1,600 pairs of adult female twins, with an average age of 50, who completed a confidential questionnaire about their sexual history and attitudes. The scientists worked out the genetic component of infidelity and other traits by comparing the results for identical twins, all of whose genes are the same, with fraternal twins, who shared half their genes but grew up together.