A new study is creating the perfect excuse for cheating spouses who are caught out: infidelity may be inherited.
Both men and women may be more likely to have affairs as a result of the genes passed down by their parents, according to research.
Scientists have even identified a single gene which has variations that make women more likely to commit adultery.
The study, carried out by researchers at the University of Queensland and other institutions, examined the roles played by genes in human affairs.
Dr Brendan Zietsch, research fellow at the university’s school of psychology, who led the study, said: “Our research clearly shows that people’s genetic make-up influences how likely they are to have sex with someone outside their main partnership.
“Isolating specific genes is more difficult because thousands of genes influence any behaviour and the effect of any individual gene is tiny.
“But we did find tentative evidence for a specific gene influencing infidelity in women. More research will be needed to confirm this finding.’’
Experts have never fully understood, in scientific terms, why men and women have affairs. For men, having a number of partners can lead to more offspring, which would traditionally have been seen as advantageous for the continuation of blood lines.
The University of Queensland researchers examined data on more than 7,300 twins aged 18 to 49, all of whom were in long-term relationships.
Some 9.8 per cent of the men and 6.4 per cent of women had had two or more sexual partners in the previous 12 months.
The researchers compared the difference in these rates between identical twins, who share all their genes, and non-identical twins, who do not. Genetic modelling was then used to estimate the heritability — the proportion of the difference attributable to genetic factors.
The results showed that 63 per cent of unfaithful behaviour in men was down to inherited genes, and 40 per cent in women, rates which surprised the scientists, who then looked for what genes could be involved.
They found women with certain variations in a gene called AVPRIA were more likely to be unfaithful. The gene is involved in production of the hormone arginine vasopressin which is known to be involved in the regulation of social behaviour and has been linked to differences in philandering behaviour in voles.