Cheating is generally thought to be one of the worst things that someone can do within a relationship. It’s a violation of trust and a complete betrayal of the monogamy most people expect from a relationship. Yet it’s incredibly common. I’ve never met anyone who thinks that cheating is anything less than horrible, but still it happens. People who have been cheated on are often left asking the question “why?” Well, there are probably a lot of reasons why cheaters cheat, but I’m a genetics nerd, so I like to look at this from an evolutionary perspective. Although it’s far from a complete answer to the question, it’s still interesting to think about it. We might just be programed to cheat. It might just be a search for good genes.

Humans seem to be polygamous by nature, so there’s a pretty strong urge within men to breed with multiple women, so one would think that men are more likely to cheat on their partners than women are, right? That makes sense and goes along with our cultural view of men being horny dogs who can’t control themselves (which is a view that results from the natural polygamy in humans), but men actually aren’t any more likely to cheat than women are. In fact, women may even be more likely to cheat on men, and it comes down to genes.

Let’s talk about birds for a minute. A lot of species of birds are monogamous, yet it’s not uncommon for females to cheat on their partners with another male. It’s a risky decision, because if the male were to find out that the eggs weren’t his, he’d probably abandon the female and leave her and her chicks to die, yet it’s a risk that’s often deemed worth taking. Say you’re a female bird who just landed in a nice meadow great for raising babies, but maybe you’re not the first one there. If you’re the 60^th female to land there, you’ll likely have to settle for the 60^th best male to mate with. That kind of sucks, because you want your babies to be good and healthy but your mate isn’t that great, so he isn’t all that likely to produce strong babies with good genes. Your neighbor’s mate is big and strong, though… And he probably wouldn’t mind a chance to make more babies, either, so it seems like a great solution. As long as you don’t get caught, you got the good genes from your neighbor and your mate is blissfully unaware that the chicks he’s helping raise aren’t even his.

Back to humans. In modern society, when someone has an affair, the last thing they want to come from it is a pregnancy, but the evolutionary factors behind the behavior still influence people. Not everyone cheats, though, and it’s unlikely that those who don’t just happen to always have the best possible gene donor in the area, so that’s about where social factors and the fact that humans have morals and higher reasoning come in. Maybe the people less likely to cheat on their partners are more able to resist the more primal of our impulses, and maybe that’s why they say “once a cheater, always a cheater,” because if someone gave into it once, they’re more likely to do it again. Then again, maybe not. I’m not a psychologist or sociologist and the dynamics of human interactions and relationships are way too complex and diverse to put a simple “here’s why” on a behavior. Cheating isn’t unique to humans and there’s a clear reason why other species do it, so it makes a lot of sense that those same reasons apply to humans, but people are complicated creatures, so behaviors aren’t one dimensional.