Twin study reveals genetic role in female infidelity

A confidential survey of more than 1,600 pairs of female twins has revealed that genetic factors have a substantial impact on how likely women are to cheat on their partner and how many sexual partners they will have. This is the first ever study to look at the genes underlying these influences in humans.

The results of the new research -- led by Professor Tim Spector, Director of the Twin Research Unit at St Thomas's Hospital, London -- were revealed by Professor Spector during a press briefing at the Science Media Centre today (Wednesday, November 24). The full research study will be published in the December edition of scientific journal Twin Research.

Female twins from the St Thomas? Twin Research Unit database answered a range of questions in a confidential questionnaire relating to their sexual atttitudes and behaviour. They reported previous episodes of infidelity, total lifetime number of sexual partners and also their attitudes towards infidelity. The average age of respondents was 50, their average number of sexual partners was between four and five, just over 20% admitted to infidelity, 25% were divorced and 98% were heterosexual.

Professor Spector says: ?Not surprisingly, the average number of sexual partners was significantly higher among respondents who had been unfaithful compared with those who had remained faithful -- a mean of eight compared with four. Headline findings of the research study include:

* Genes are an important influence in explaining variation between women in both infidelity and number of sexual partners ? with a heritability of 41% and 38% respectively.

* Further analysis of these results failed to support the hypothesis that a gene implicated in previous research into patterns of sexual behaviour among rodents (AVPR1A or vasopressin gene) could explain the observed variation in human sexual behaviour.

* However, the study did find some evidence that genes in three other chromosomal areas (chromosomes 3, 7, 20) could be implicated.

* In contrast, attitudes to infidelity are not influenced to any significant degree by genetic factors ? environmental factors including society, education or religion prevail.

* Believing infidelity was wrong in principle prevailed even in a significant proportion of those women who admitted having been unfaithful, highlighting the distinction between attitudes and actual behaviour.

Professor Spector says: "By demonstrating the heritability of female infidelity and number of sexual partners in humans, this study justifies additional genetic and molecular research on human sexual behaviour. "The fact that psychosocial traits such as number of sexual partners and infidelity appear to behave as other common complex genetic traits in humans, in that they have a heritable component, lends support to evolutionary psychologists' theories on the origins of human behaviour."

Professor Spector believes that the logical conclusion of his team?s new research may be that infidelity and other sexual behaviours persist because they have been evolutionarily advantageous for women at some time.

The Twin Research Unit was originally set up at St Thomas' Hospital in 1992 to look at the role that genes play in the development of rheumatic diseases in older women and has now expanded to look at most common diseases, behaviours and traits in both men and women. This latest research study involved women only since the St Thomas' database of twins still has a female bias for these historical reasons.

If you are a twin (identical or non-identical) aged over 15 who would like to volunteer to join the 10,000 twins on the register of the Twin Research Unit at St Thomas' Hospital, please call 020 7188 5555.


The research paper - 'Genetic Influences on Female Infidelity and Number of Sexual Partners in Humans: A Linkage and Association Study of the Role of the Vasopressin Receptor Gene (AVPR1A)' - will be published in the December edition of Twin Research (Vol. 7, No. 6). A copy of the full research paper is available from Matt Akid or Claire Bithell.

The above article was a press release from Guy's and St. Thomas' hospital in London, dated 24 November 2004

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