Genetic factors influence female infidelity and the number of sexual partners women have, British scientists said on Wednesday.

They studied the responses of 1,600 pairs of identical and non-identical twins in a confidential survey to look at the impact of genes on behavior.

“We found that around 40 percent of the influence on the number of sexual partners and infidelity were due to genetic factors,” Professor Tim Spector, director of the Twin Research Unit at St Thomas’ Hospital in London, told a news conference.

But he added that environment and upbringing also play a part in explaining the variation in infidelity between women.

“The fact that psychosocial traits such as number of sexual partners and infidelity appear to behave as other common complex genetic traits in humans … lends support to evolutionary psychologists’ theories on the origin of human behavior,” Spector said.

The scientists questioned the twins about their sexual behavior, total number of partners and their attitudes about infidelity. Twenty-two percent admitted that they had been unfaithful.

Genetic factors did not appear to influence the women’s attitudes to infidelity. Many of the women in the study, even those who admitted being unfaithful, said they thought it was wrong.

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