Though some people don't view being non-monogamous as that big of a deal and don't believe that their relationship will suffer if either they or their partner cheats, for others, finding out that their partner cheated on them can feel like all of the air is being sucked out of the room. Lots of people wonder why others cheat, and if your partner cheated on you, you might be especially curious as to their reasoning. But there are actually changes that happen in a man's brain when he cheats (or before he cheats) that might explain what's going on. That being said, in science, there's a difference between correlation and causation, so just because your partner has some of these things or experiences some of these things doesn't necessarily mean that he's definitely going to cheat, it just might make him more susceptible to doing so.
When you find out that your partner has cheated, however you may define it, it's not unusual to feel at least a smidgen of temporary betrayal at some point. You also might have a lot of questions about their motivation and reasoning, how it all went down, why that person, and more. Though you and your partner may or may not ever talk in detail about those things, and though your relationship might not make it, understanding some of what might be going on in their brain before and when your partner cheats is still something about which you may want to know more. Even if it only serves to satisfy your own curiosity.
1Their Dopamine Receptor Gene Is Longer
As it turns out, there might actually be some genetic factors that explain more about what's going on in a man's brain when he cheats. A 2010 study published in the journal PLoS One found that those who had a long allele version of the dopamine D4 receptor gene were more likely to report that they'd cheated on their partner in the past. Dopamine is a neurotransmitter that's typically associated with pleasure and this particular genetic variation could potentially be more likely to be present in those who cheat.
2Once They Cheat Once, They Feel Less Guilty When They Cheat Again
Cheating occurs for so many different reasons and there are many different factors that can influence someone's likelihood of cheating. But once you cheat the first time, you might be more likely to cheat again. A 2016 study published in Nature Neuroscience found that, over time, your brain gets more used to lying, which makes it easier for you be deceptive each time you do it.
3They Have Lower Levels Of Monoamine Oxidase A
If your partner is someone who values unique experiences, competition, and power, they might fall under the category of people known as "sensation seekers." Newsweek reported that this group of people tends to have lower levels of monoamine oxidase A — the enzyme that helps dictate the levels of dopamine that are in your brain. Because of this, they might be more likely to seek out experiences like affairs and additional partners.
4They Have A Certain Type Of Vasopressin Receptor
In a piece that he wrote for the New York Times, Dr. Richard A. Friedman, MD, a professor of clinical psychiatry and neurobiology expert, noted that research from the Karolinska Institute in Sweden found a connection between partners who reported lower levels of satisfaction in their marriage and men with a certain type of vasopressin receptor. Friedman was careful — and quick — to point out that this doesn't mean that every man with that kind of vasopressin receptor gene will cheat or otherwise have a terrible marriage, however. Again, there are a number of different factors that influence these complicated issues and just because researchers found a connection between these things doesn't necessarily mean that one causes the other.
5They Have Higher Levels Of Testosterone
Testosterone levels could also potentially play a role. A 2007 study published in Hormones and Behavior found that people who tend to cheat on their partners also tend to have higher levels of testosterone than those who stay monogamous. This doesn't mean that higher testosterone is what made them cheat, but it could be possible that this biological difference may have played a role.
6They Lose Their Ability To Manage Risk Because It Doesn't Seem Like As Much Of A Risk
In an interview with Newsweek for the aforementioned article, psychologist Brian Gladue said that if they regularly take risks and things generally tend to work out, their ability to evaluate potential risks and the consequences associated with them lessens. So if your partner takes a lot of risks in general or has cheated without their partner knowing before, that might affect how they think about cheating.
Cheating on your partner isn't OK, but there are some biological factors that might make you more prone to doing so. Still, your decision of whether you're going to cheat on them or not plays a central role. It's important to remember that you or your partner still have to ultimately take responsibility for your actions, whatever they may be.