Unzipping cheaters' genes
It could be the perfect excuse for cheaters who are caught out: the predilection for infidelity might be inherited.
Both men and women might be more likely to have affairs because of the genes passed down to them by their parents, according to research.
Scientists have even identified a single gene that has variants that make women more likely to commit adultery.
The study, by researchers at the University of Queensland, Australia, and other institutions, examined the roles played by genes in human affairs.
Brendan Zietsch, a 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 difficult because thousands of them influence behaviour and the effect of any one is tiny. But we did find tentative evidence for a specific gene influencing infidelity in women. But more research will be needed.''
The University of Queensland researchers examined data on more than 7300 twins aged 18 to 49, all of whom were in long-term relationships. About 9.8% of the men and 6.4% 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. The results showed that 63% of unfaithful behaviour in men was attributable to inherited genes, and 40% in women.