Why do people cheat? Psychologists reckon they have a good handle on this question when it comes to men, but for women the picture is less clear. A new study surveyed people from 19 countries to explore this question, but there were no simple answers to be found.

Being cheated on can be among the most traumatic and difficult life experiences. It’s risky for the cheater too, who will often lose not only their relationship but also the esteem of others in the community – albeit some research suggests cheaters feel less guilt than we might think.

This explains science’s continued fascination with why people cheat, who is more likely to cheat, and factors that might help predict or prevent it. One question that has sparked vigorous debate in this field is whether there are gender differences at play.

“While scholars largely agree men’s infidelity evolved by increasing offspring quantity,” begins the new study, “the evolutionary drivers of women’s infidelity remain debated.” As lead author and University of Melbourne PhD study Macken Murphy told PsyPost, “In a way, there are too many good explanations for it!”

As Murphy and colleagues explain in their paper, psychologists believe that the drive to father more offspring by having more partners explains much of male infidelity even now, in the age of contraceptives.

When it comes to women, however, this is a less compelling explanation – having multiple sexual partners doesn’t necessarily mean more kids. Many other theories have been proposed, including the idea that having multiple partners allows women to obtain more resources, or that women cheat to punish bad behavior in their primary partner or to drive them away and help them end the relationship. 

To try and sift through some of these theories, Murphy and colleagues surveyed 254 heterosexual, cisgender men and women using an online platform. The group had a mean age of 30.5 years, and all participants self-described themselves as having had sex outside of an otherwise exclusive relationship.

All of the participants were English speakers, but they covered a wide range of countries across six continents, with the majority being spread between South Africa, the UK, and Mexico.

The team used adapted versions of some well-established rating scales to assess the participants’ physical, personal, and parental (that is, their perceived ability to be a good parent) attraction towards both their primary partner and the person they cheated with. They also asked them to describe in their own words why they had an affair. 

The women in the study generally found their affair partners more physically attractive, and their primary partners more parentally attractive. That provides some evidence for the “strategic dualism” theory, which suggests that conceiving a child with someone outside their relationship allows women to obtain “good genes” while remaining with a partner they perceive as a good father. 

Unexpectedly, the patterns emerging from the men surveyed in the study were very similar to those in the women.

“Finding that men were strategically dualistic as well – prioritizing physical attraction in affair partners and parental ability in primary partners – was a surprise,” Murphy told PsyPost. 

When women were asked to describe in their own words why they had cheated, a number of different motives emerged – seeking novelty, feeling dissatisfied with their primary partner, and revenge being among them. The quantitative data provided little evidence that women were cheating to find a new long-term partner, but some did cite this as a reason in their free-text response.

“Our qualitative data should be interpreted with caution,” write the authors. Not everyone will feel comfortable giving a true account of their motives for cheating. Another key limitation is that the authors did not collect data on whether or not people had children, which might have affected their decision-making.

Ultimately, the authors concluded that “seeking a ‘primary explanation’ for infidelity, as we have in this study, is a low-resolution approach to the issue.” In other words, there are no simple answers here.

“People cheat for a variety of reasons, consistent with a variety of evolutionary hypotheses.”

The study is published in the journal Evolution and Human Behavior.