Warning: This article may be deadly for your trust issues.

Men are always presumed to want to sleep with as many people as possible because of an evolutionary desire to ensure the future of their family tree. But a new study suggests that some women may also have a biological urge to cheat.

The New York Times reported on a study by the University of Queensland in Australia to determine whether some people are just more inclined toward infidelity. It looked at the vasopressin receptor gene—a hormone that affects trust, empathy, and sexual bonding in animals—to see if it may be responsible for a person’s desire to stray from the comforts of a monogamous relationship, or “extra pair bonding,” as sociologists call it.

The study—of 7,400 Finnish twins and their siblings who had all been in a relationship for at least one year—found a “significant association” between five different variants of the vasopressin gene and infidelity in the women. The Times noted that 9.8% of the men and 6.4% of the women reported two or more sexual partners in the previous year, and 40% of the “variation in promiscuous behavior in women could be attributed to genes.”

“Although this is the largest and best study on this, it’s not clear why there was no relationship between the vasopressin gene and promiscuous behavior in men,” the Times said. But, of course, having more sexual partners does not really affect a woman’s chances of having more children. So why do some women have an urge to cheat?

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, behaviors that activate the brain’s reward circuit. Sex, money and drugs, among other things, trigger the release of dopamine from this circuit, which conveys not just a sense of pleasure but tells your brain this is an important experience worth remembering and repeating. And, of course, humans vary widely in their taste for novelty.

It is clear that, for both sexes, the biological answers to a lot of questions over infidelity, peer bonding, and harmony between couples is to be found in the oxytocin and vasopressin genes.

Another study from Sweden found that there is a “significant association” between one variant of oxytocin and a lack of affection for a partner, as well as a correlation between one variant of the vasopressin receptor gene and lower marital quality reported by their spouses.