Infidelity — commonly known as cheating — means different things to different couples. For some, the definition may be stricter than others and include activities or connections that some couples would consider OK behavior. A new study out of Norway takes a look at the way men and women see cheating differently and points to evolutionary reasons for why there are discrepancies.

“Men and women’s psychology is similar in most areas — but not when it comes to reproduction,” said professor Mons Bendixen, from the Norwegian University of Science and Technology (NTINU), in a press release.

He teamed up with fellow NTINU professor Leif Edward Ottesen Kennair and Professor David Buss from the University of Texas, Austin, to conduct the study featuring over 1,000 participants. Norway is considered one of the world’s top countries in terms of gender equality. Fathers are expected to help out and be there for their children, and there is paternity leave available for them. Support for single parents also makes it easier to raise a child alone if need be. Still, the differences between men and women when it came to infidelity were stark.

Recent research has distinguished two main types of cheating: sexual infidelity and developing an emotional attachment to a person other than your significant other.

On the men’s side, it was sexual infidelity that was considered the most worrisome. An evolutionary perspective explains this through the way men behaved over many generations. A man needs to decide if a child is really his, an issue men have struggled with from the beginning of time. Insecurity about a child’s paternity could lead a man to wonder if it’s worth it to invest all of his resources and protection in that mother and child. Using this approach, men’s jealousy could be a reaction to possible sexual infidelity, which developed to help reduce the chances that his partner is cheating and a child born would not be his.

Women developed a different set of values through time, and a common theme among women even today is that a man having sex with other women isn’t nearly as bad as him developing an emotional attachment to another.

Generations ago, in order to survive, women reacted with jealousy to men who showed signs they may be investing time and resources on another woman. This could lead to abandonment, and a women would need to raise a child on her own. It is for this reason that women respond to the threat of another woman using up her partner’s time and protection.

Psychology has another perspective on why these differences exist, focused on a cultural perspective rather than an evolutionary one. This second view maintains that in a place with a high degree of gender equality would have less differences in the way men and women react to infidelity, and a culture that assigns women and men certain roles would shape their perspectives as well.

“The cultural gender role perspective believes that jealousy is learned, but we feel confident that these reactions are mechanisms that are a part of an evolved human mind, given comparable findings across several nations,” Bendixen said.

Source: Bendixen K, et al. Jealousy: Evidence of Strong Sex Differences Using Both Forced Choice and Continuous Measure Paradigms. Personality and Individual Differences. 2015.