When it comes to infidelity, men often get away with blaming their behaviour on the 'biological urge' to spread their seed. But recent research suggests that women may also inherit the impulse to cheat.
In fact, scientists have found one gene in particular that seems to be linked to a woman's likelihood of being unfaithful.
A study published at the end of last year looked at 7,400 sets of twins in Finland aged between 18 and 49 in long-term relationships. Out of the participants, 9.8 percent of the men and 6.4 percent of women had had at least one affair in the past 12 months.
The researchers then compared the difference in the rates of cheating between identical twins, who share all their genes, and non-identical twins, who don't. The results showed that 63 percent of the variation in infidelity in men and 40 percent in women could be attributed to genetics.
"Isolating specific genes is more difficult because thousands of genes influence any behaviour and the effect of any individual gene is tiny," lead researcher Brendan Zietsch, from the University of Queensland in Australia, said in a press release. "But we did find tentative evidence for a specific gene influencing infidelity in women."
The gene in question is the vasopressin receptor gene, which is involved in creating trust, empathy and sexual bonding in animals, so it makes sense that this would have some kind of affect on sexual behaviour. But, interestingly, this gene appeared to have no effect on promiscuity in men.
Obviously correlation doesn't equal causation, but research in animal models also backs up the idea that vasopressin - as well as other hormones linked to our emotions, such as dopamine and oxytocin - may play a larger role in fidelity than previously thought, as psychiatrist Richard A. Friedman reports for the New York Times.
A lot of this research has focussed on the vole, a little rodent that has two closely related species with very different lifestyles - the prairie vole is monogamous, while the montane vole is sexually promiscuous.
Researchers have found that the differences in the sexual behaviour of these two species can be explained by the different positioning of vasopressin receptors in their brains, which changes the hormones' effects. In fact, scientists have shown it's possible to take a cheating male montane vole and make him faithful, simply by changing the expression of the vasopressin receptor gene. They can do the same with females by altering the oxytocin (AKA the 'love hormone') receptor gene.
So what does all this mean for your chance of being cheated on by your significant other? While more research needs to be done, the research could help biologists answer one their biggest questions: why, evolutionarily speaking, are women driven to cheat?
For men, the benefits are clear, but for females, who can only give birth to a limited number of offspring, the perks are less obvious. Maybe it all comes down to the fact that, depending on our genes, for some of us, cheating just feels good, as Friedman explains:
"There may be no clear evolutionary advantage to female infidelity, but sex has never just been about procreation. Cheating can be intensely pleasurable because, among other things, it involves novelty and a degree of sensation seeking, behaviours that activate the brain's reward circuit … which conveys not just a sense of pleasure but tells your brain this is an important experience worth remembering and repeating."
Either way, the key to understanding why humans, and other animals, are faithful (or not), may lie in the genetic programming of a few key hormones. Read Friedman's piece over at the New York Times to find out more.