Beyond Body Count: The Scientific Predictors of Infidelity

The research-backed truth about infidelity: from eye movements to evolutionary instincts, what science actually reveals about who cheats and why.

Most therapists approach the subject of infidelity as if they were handling hot soup in a flimsy paper cup. In this post, I venture onto the hazardous path of reviewing scientific data that predicts cheating. I keep the tone light because I believe humor creates a buffer between facts and their often painful reality.

Today, we expect a lot more from our romantic partners than we did in the past. Couples expect their partners to be their best friends, passionate lovers, co-parents, financial partners, and emotional support buddies. These unrealistic expectations, typical of modern marriages, make infidelity far more devastating than it was when marriage was primarily a socioeconomic arrangement.

Meanwhile, modern culture—and its pernicious ally, marketing—constantly tells us that we deserve the best, that life is short, and that better options are just a swipe away. Our desires haven’t changed, but we feel entitled to pursue them. We’ve created a situation where obsessive fidelity and chronic temptation coexist. The result? We’re more outraged by cheating than ever before, yet we’re now engaging in it at rates that would baffle our grandmas.

Many people desperately want to believe that infidelity is random. The data tells a different story. Cheating is both more common and more predictable than most people are willing to acknowledge. Worse, not everyone has the same potential to cheat. Some people remain faithful for decades, while others treat monogamy as a mere suggestion. Understanding what distinguishes serial cheaters isn’t about being judgmental or cynical. It’s about making smarter decisions when dating.

To understand what predicts infidelity, we’ll examine data from the fields of evolutionary psychology, behavioral science, relationship research, and anthropology. Data are facts. And facts don’t care about morals; they only reveal patterns that emerge when examining the numbers. If you’re going to build a life with someone, it’s only fair to try to figure out who will protect the relationship and who’s more inclined to treat it as disposable.

The truth about monogamy

Across cultures and history, socially enforced lifelong monogamy is the exception rather than the rule. As it turns out, monogamy is more of a successful social invention than a biological imperative. Humans have evolved with tendencies toward pair bonding that allow for commitment, as well as enough curiosity, psychological complexity, and sexual drive to keep therapists fully employed.

Throughout history, people have engaged in various forms of relationships, ranging from serial partnerships to polygamy. Strict lifelong monogamy emerged relatively late, once concerns about protecting property and preventing young men from stabbing each other became pressing. Biology gives us attachment, while culture sells us vows, engagement rings, and moral expectations, hoping they’ll hold up under pressure. When they don’t, we call it betrayal because monogamy isn’t biologically guaranteed; it’s a moral covenant.

Is gazing considered cheating?

If you’re looking to start an argument at your next dinner party, here’s a fun fact: researchers tracking eye movements found that people who looked away from an attractive option just a few milliseconds faster were 50% less likely to cheat. Barely a blink. Yet this tiny difference predicts whether someone will jeopardize their relationship. You don’t need to time your partner’s eye movements with a stopwatch. You can tell the difference between someone who notices an attractive person and someone who studies them as if prepping for a final exam.

There’s a cultural narrative that noticing attractive people is benign. But there’s a world of difference between acknowledging someone’s attractiveness and maintaining what researchers call “extra-pair interest,” which is a fancy way of saying “mental spreadsheet of backup options.” It’s the difference between a casual glance and persistent, motivated staring.

Besides, when someone spends serious time following Instagram models, fantasizing about celebrities, or consuming enough explicit content to qualify for frequent flyer miles, they’re not just passively observing the world. They’re actively window-shopping. And one large-scale study found that regular consumers of online explicit content were twice as likely to have an affair. The mechanism isn’t exactly quantum physics: if you’re constantly browsing the catalog, eventually you’re going to want to place an order.

The league theory that didn’t get invited to the party

Evolutionary psychology collides with rom-coms when we consider that we’ve adapted to exploit our own mate value. This creates a twisted situation when there is a significant mismatch in attractiveness between partners. Translation: If someone can consistently “do better” than you, statistics suggest they eventually will. I know, it sounds like something a Reddit post. But the data is annoyingly consistent. More attractive people also tend to report lower relationship satisfaction and commitment on average. Not because they’re the villains, but because abundance creates incentives.

The person who “married up” too far from their own league often expends a great deal of energy managing the parade of competitors trying to shoot their Cupid arrow. Once a certain threshold of attractiveness is reached, more of it doesn’t improve the relationship; it only increases the liabilities.

The insight isn’t to date people who make you go “meh.” It’s recognizing that once someone crosses your personal attractiveness threshold, their character becomes far more important than their potential to moonlight as a sports calendar model. The deepest connections aren’t built on looks anyway. They’re built on whether you laugh at the same things, share values, communicate well, and don’t want to smother each other with a pillow after a long weekend together.

Socio-sexuality: boring word, important concept

One of the most robust predictors of infidelity has a terrible name: socio-sexuality. It’s basically someone’s enthusiasm for casual, no-strings-attached sex. Yep, people who genuinely enjoyed the one-night-stand lifestyle while single are statistically way more likely to cheat when partnered.

This is hardly surprising when you consider what cheating actually is: uncommitted mating. If you don’t enjoy a particular menu item when it’s free to order without consequences, you’re far less likely to risk their relationship for it when there’s a cost attached.

This is where the “body count” debate misses the point. Five partners in committed relationships over a decade tell a completely different story than five partners from last semester’s bar crawls. The question isn’t just “how many?” but “in what context, and within what emotional framework?” It’s like asking, “How many drinks have you had?” The number doesn’t matter as much as the context: over the course of a year of dinner parties or last Friday night.

The Dark Triad

The Dark Triad isn’t the name of a metal band. It refers to a trio of “negative” personality traits—narcissism, Machiavellianism, and psychopathy—that share malevolent characteristics. These traits are highly predictive of infidelity.

Ironically, these same traits often make someone appear initially attractive. The swagger of narcissism, the strategic charm of Machiavellianism, and the emotional intensity of psychopathy can be compelling, especially when deciding if someone if worth a second date. Ted Bundy, the infamous serial killer, was known for his cunning ability to appear charming and articulate.

My advice? Watch how your date treats the waiter, their mother, their ex, and small animals. If someone is casual about betraying others when there’s nothing to be gained, believing that they’ll make an exception for you is magical thinking—the kind that belongs in fantasy novels and generally doesn’t end well.

Let’s not forget uncomfortable family history. The propensity to cheat is estimated to be around 40% heritable, similar to the heritability of borderline personality disorder. While this doesn’t mean the children of cheaters are doomed to repeat the pattern, it does suggest that genes and learned behaviors matter. Growing up and watching infidelity be normalized as a casual habit can affect one’s internal moral compass.

When chickens come home to roost

People who cheat are more likely to be cheated on. In fact, revenge is the third most common reason women give for being unfaithful—they even the score.

This creates a thorny dynamic as men age. Data shows that social status increasingly trumps physical attractiveness for men over time. A 50-year-old guy who is socially successful often has more options than he did at 25. Research suggests that he’s also more likely to pursue those options with younger women. This has major implications for high-status guys seeking asymmetrical relationships. Many successful men want an “open” relationship, where “open” means “open for me, not for you.” Beyond the obvious ethical issues, the practical reality is harsh: Without reciprocity, the relationship becomes unstable. The faithful partner isn’t thinking, “They’d never do this to me,” when tempted. They’re thinking, “Why do they get to have all the fun?” When opportunity presents itself—and it will, because both partners have options that shift with age and status—the sense of unfairness becomes permission. That’s not exactly a foundation for long-term commitment.

Loyalty begets loyalty. Commitment signals commitment. This isn’t me preaching from a moral high horse. It’s what comes up when you run the numbers on who strays and why.

The dissatisfaction with a permission slip

While temptation sets the table, relationship dissatisfaction provides the permission to eat. The number one cited motivation for infidelity in studies? Being unhappy in the primary relationship.

This means that maintaining the emotional, physical, and sexual aspects of the relationship isn’t just a good idea. It’s structural foundation. People tend to cheat “up” in terms of physical attractiveness, suggesting that letting yourself go completely creates vulnerability. A less interesting bedroom life creates vulnerability. Physical and emotional distance create vulnerability through opportunity and the particular loneliness that comes from not receiving affection or not being seen.

None of this means every unhappy person cheats, or that staying attractive guarantees faithfulness. But these are the factors that consistently show up in study after study, across cultures and decades.

That said, reality is often more complex when it comes to justifying infidelity. People fall victim to what psychologists call the actor-observer bias. If you cheat, you’re untrustworthy, selfish, and weak. If I cheat, it’s because of the situation I was in. We justify our own actions and blame our partner’s character.

The dilemma of gender differences and motivations

Things become more controversial and complicated when we consider whether men and women cheat for the same reasons.

On the one hand, there’s data based on what people openly admit and what evolutionary psychologists theorize. On the other, there’s a more subtle and complex emotional reality involving relationship dynamics, unconscious desires, and hidden motivations fueled by guilt. I’ll present both sides of the story.

Roughly 70% of men who cheat cite opportunistic sexual variety as their primary motivation. Many claim their relationship satisfaction has little to do with it. It’s less about what’s missing at home and more about the biological draw toward novelty, excitement, and the thrill of feeling valued.

Women’s infidelity seems to follow a different logic. For women, relationship dissatisfaction is reported to be a much stronger predictor of cheating. But here’s the striking part: approximately 70% of women who cheat report falling in love with their affair partner. This isn’t casual recreation—it’s mate-switching in action. The mate-switching hypothesis suggests women don’t typically cheat for variety; they cheat to transition. The affair might serve as an exit strategy (emotional support to leave or unconscious sabotage), an upgrade attempt (testing someone with better qualities before switching), desirability testing (confirming they can still attract alternatives), or backup maintenance (keeping options warm in case the primary relationship fails).

This doesn’t mean women are calculating schemers any more than men are uncontrollable libido machines. These are patterns, not deterministic scripts. But understanding the different motivational architectures helps explain why the same “solutions” don’t work for different types of infidelity.

But there’s another script. Renowned therapist Esther Perel rejects the stereotype that men cheat for sex while women cheat for emotional connection, arguing these differences are culturally constructed rather than biological. She notes that when women have autonomy and resources, gender differences in infidelity largely disappear. For Perel, the primary driver for both genders is “deadness” in relationships—emotional numbness and neglect—and people often stray not to find another person but to reconnect with a lost version of themselves.

In my experience, it is far more important to understand the particular dynamics of the relationship than to attempt to diagnose the type of infidelity based on gender stereotypes or evolutionary mechanisms. A one-size-fits-all approach to betrayal overlooks fundamental differences in emotional motivation and the silent plots operating beneath the surface.

Your built-in infidelity detector

Perhaps the most fascinating finding is about detection. Yes, there are classic signs—phone suddenly password-protected, unexplained late nights at “work,” behavioral changes that feel off. But I’ve been consistently struck by how many people describe “just knowing” before they had a shred of evidence.

We evolved over hundreds of thousands of years in conditions where detecting infidelity mattered enormously. Your ancestors who were better at spotting cheaters had more reproductive success, which means you inherited their paranoia—er, discernment.

Your brain is adapted to pick up nuanced signals and sound the alarm when something feels off. It’s probably oversensitive—evolution favored false alarms instead of missed betrayals. Better to be suspicious and wrong than oblivious and raise someone else’s kid. (That’s evolution talking, not me.)

The therapeutic balance is this: let yourself relax into your relationship. Don’t be that paranoid person timing eye movements with a stopwatch. But if that internal alarm goes off persistently, don’t dismiss it as irrational anxiety. Check it out. Your intuition deserves investigation, even if it’s often crying wolf.

The uncomfortable bottom line

Nobody chooses a partner solely to minimize the risk of cheating, nor should they. Love isn’t a statistical risk-assessment model, and anyone who approaches it that way is going to end up alone with their Excel spreadsheet.

Recognizing these behavioral patterns can help us make better dating choices and maintain healthier relationships. People are predictable in many ways. Research consistently supports the common-sense wisdom that would make your grandma nod in approval. Choose someone who is your equal, has solid character, who shares your values, comes from a stable background, has a credible history, and takes commitment seriously. Then, be loyal, invest in the relationship, and trust your instincts.

I know. It doesn’t sound romantic. But it’s real. Frankly speaking? That’s more useful than romance when you’re trying to build something that lasts longer than the honeymoon phase.

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