What would upset a man more, catching his girlfriend having sex or knowing she's fallen in love with someone else? What about a woman? In the largest study on relationship cheating, men and women had opposite reactions and confirmed the typical stereotypes of jealousy. Researchers from Chapman University studied the different reactions that are born out of infidelity and published their findings in the journal Archives of Sexual Behavior.

“There has been significant disagreement about whether or not men and women tend to differ in their responses to sexual and emotional infidelity,” David Frederick, the study’s lead author and psychologist from Chapman University, said in a press release. “Most research relies on small samples or college samples. We set out to examine a broad and diverse sample of Americans.”

Researchers asked 64,000 American men and women of varying sexual orientation how they would react to finding out their significant other was cheating on them. Did the sexual infidelity bother them more than the emotional infidelity? Answers varied depending on gender. “Heterosexual men really stand out from all other groups,” Frederick said. “They were the only ones more likely to be most upset by sexual infidelity.”

Male vs. Female Reactions to Cheating

The study participants were asked to picture their partners having sex with someone else but not falling in love with them. Then, they were asked to imagine their partners were in love with someone else but weren’t having sex with them.

It turns out, 54 percent of heterosexual men surveyed were more upset about the sexual, physical infidelity than they were about any emotional connection their girlfriend or wife could have made. Only 35 percent of the heterosexual women surveyed were bothered by the sexual infidelity more than the emotional aspect. Younger participants were also much more upset by sexual infidelity than older participants, despite their gender or sexual orientation.

“The responses of men and women to the threat of infidelity range from intense pangs of jealousy to elaborate displays of attention to woo their partner back,” Frederick said. “Jealousy can also trigger harmful and violent behavior, so it is important to understand what are the most potent triggers of jealousy.”

When it came to people with non-heterosexual orientations, they weren’t bothered as much. Bisexual men and women reacted very similarly when it came to how they felt about sexual or emotional cheating. Gay men and lesbians also felt the same about it. But then again, Frederick says there’s not enough research to conclude why gay and bisexual men don’t react as viscerally as straight men do.

Regardless, he says, whether the infidelity is sexual or emotional, it is bound to hurt men and women of any sexual orientation. It just depends which they believe will hurt them more. Why are men more up in arms about sexual betrayal than they are about love?

The Lonely Straight Man’s Problem

Researchers looked to evolution for answers. Men face a problem women will never have to face. Paternal uncertainty is the focus of most Maury episodes: Who is the father? They never really know if their child is genetically related to them, so for a man to imagine his potentially child-bearing woman engaging in sex, it creates an instinctual threat. That man’s offspring is no longer a sure thing, and it could possibly be someone else’s. Even if he and his girlfriend or wife aren’t planning on having children, or even if she is infertile, the instinct will still be locked into place.

Another theory is the straight man’s great sexual prowess — at least, that’s what society has trained the man to believe he needs to have. You’ve seen it in the animal kingdom, the lion dominating the female because it’s his territory. A similar effect is happening, in hiding beneath a more intellectually evolved level. A person’s reaction to sexual versus emotional infidelity has been shaped by societal, environmental, and personal factors.

Source: Frederick D and Fales M. Archives of Sexual Behavior. 2014.