There’s Science Behind Why Some Couples Look Like They’re Related

Updated: Jul. 11, 2024

Research into how we choose our mate reveals some surprises.


You may not realize it, but when you gaze into your partner’s eyes, there’s a good chance that you’re looking at a modified reflection of yourself. Researchers have found that people choose mates who tend to be of similar size, shape and ethnicity as themselves… and they may even have facial features in common.

Take Lot Geels of Amsterdam and her American husband Brock Mosovsky, for example. “We both have blond hair and blue eyes,” says Lot. “Neither of us is very tall. We’re both built athletically and we’re both mainly of European descent.”

Even if you don’t look like your spouse, you likely share non-physical characteristics, according to a growing field of research, like education level, socioeconomic standing, religion, personality traits, even core values.

Lot and Brock fall into this category, as well. “We both have PhDs and work in research,” she says. “ We both love an active lifestyle, mainly rock climbing and skiing/snowboarding. Our world views are pretty similar, and we’re both hard-working, social and friendly people.”

Researchers have been studying the phenomenon of people with similarities pairing up—known as positive assortative mating—for decades. If you’re sure that “opposites attract,” you may be surprised by research findings, which prove that like attracts like. However, if you believe that “birds of a feather flock together,” you probably understand why people overwhelmingly seek life partners who remind them, on some comforting level, of themselves. (Here are 28 little things you can do right now to make your marriage happier.)

“There’s an element of predictability when you date somebody of a similar background,” says Ty Tashiro, author of The Science of Happily Ever After. “They’re less threatening, less scary. They’ll be more of a familiar person from the start. Familiarity is something we find attractive.”

For most people, positive assortative mating takes place unconsciously (unless you actively seek someone from the same ethnic background or religion). Here’s how it plays out in real life:

The people in your neighborhood

The simplest reason why you may marry someone like yourself hinges on convenience and geography. “It’s more likely to meet someone from your own social circles because they go to the same church or school or university or live in the same area,” says Abdel Abdellaoui, a genetics researcher at VU University Amsterdam.

Abdellaoui found that in the Netherlands, people who live in the northern part of the country are genetically distinguishable from people in the southern part of the country because people tend to marry their neighbors. “Many of the genetic similarities can be explained by people with similar ancestries having children,” Abdellaoui says. “Our studies look at whether people assortatively mate or not, and they do, clearly. The majority of the spouse pairs resemble each other more than you would expect by chance.”

Of course, you may not always live in the neighborhood where you’re raised. If you attend university, you move onto a campus where you’re surrounded by your intellectual and socioeconomic equals. Once you start working, you may relocate to a city where it’s easier to find a job in your field, then spend the majority of your waking hours interacting with business associates with the same education level and similar socioeconomic standing.

If you’re an attorney, you’re much more likely to fall in love with an attorney or another professional you meet through colleagues or friends. You’ve still found a partner through positive assortative mating, but your similarities are less physically obvious. “Higher-educated spouses have children that have a little more genetic variation that those with lower education because they migrate less,” Abdellaoui says.

What’s cookin,’ good lookin’?

If you’ve ever done a double-take because you’ve seen a beautiful woman walking hand-in-hand with a really unattractive man, you won’t be surprised to learn that research confirms that this doesn’t happen often: Most people assortatively mate for levels of attractiveness.

“The most attractive people will pair up with the most attractive, and the medium attractiveness people will pair up and the lowest attractiveness people match up,” Tashiro says. “You can get mismatches, of course, usually due to socioeconomic differences. In general, you get attractive people with attractive people.” This doesn’t mean that unattractive people don’t find attractive people appealing. Rather, Tashiro explains, “people are self-aware of their standing in the world of attractiveness and realize that their best chance of reciprocated attraction is with those at roughly the same level.”

“There’s a thing called fidelity insurance,” says John Speakman, a professor at the University of Aberdeen’s Institute of Biological and Environmental Sciences. “What that suggests is that we choose partners that are around our level of physical attractiveness because we’re trying to ensure our partner doesn’t cheat on us.”

Weighing your options

Fidelity insurance and assortative mating may also influence choices regarding potential mates’ body types. Speakman’s research has shown that obese people tend to be married to other obese people. “If you ask people of a range of body weights what they find attractive, they all choose slim people,” Speakman says. “But obese people may not see slim people as a good choice for a lifetime partner.”

Because this is a relatively new field of study, it’s unknown whether married obese couples were obese when they met. Researchers speculate that some couples grow obese together, due to shared diet and exercise habits. For the same reasons, researchers think that slender partners stay fit because of shared healthy habits.

“People end up with partners who are similar to them in terms of attractiveness, but part of that effect is due to how people change each other over time,” says Paul Eastwick, an assistant professor at the Attraction and Relationships Research Lab at the University of Texas at Austin.

The long and short of it

Assortative mating doesn’t stop with weight. Tall people tend to pair up. So do short ones. “In the 1950s and 1960s, researchers measured couples for things like wrist circumference, head size, leg length, foot size,” says Anthony Little, lecturer at the University of Stirling. “What they found is you get small but positive correlations for a lot of these body measurements. In some ways, that isn’t surprising. Tall people pair up with tall people, heavier people pair up with heavier people.”

Because men are taller than women, couples match by height ratios, not exact measurements. A man who’s taller than 90 percent of other men will likely marry a woman who’s taller than roughly 90 percent of other women. “It’s really rare to see a tall woman with a short man,” Speakman says, “unless the man has phenomenal resources to offset his height, like Tom Cruise.”

The man in the mirror

Many people select partners who look like them in some way, whether it’s the same hair color and complexion or a similar shape to the cheekbones or jawline. “It’s all about visual exposure,” Little says. “The more we see something, the more we like it. We may like people who look like us because we are very familiar with our own features.”
Some research suggests that people are reassured by others who look like themselves. “There is some evidence that we are more likely to trust a novel face if that face is morphed slightly to look like our own face,” Eastwick says.

Valuing values

Many spouses share qualities like approachability, generosity and kindness. “Several studies conducted in different countries have shown that spouses have similar values of altruistic traits,” says Arnaud Tognetti, a researcher at the Institute for Advanced Study in Toulouse.

Some studies have found that the more time spouses spend together, the more likely they are to have similar levels of generosity and cooperation. But Tognetti, in a recent study, found that some couples share similar levels of generosity and cooperation from the start of their relationships, which may help them seem more appealing to each other.

“Cooperative behaviors may be a signal of the propensity to engage in other altruistic actions, such as childcare and provisioning,” Tognetti says. “By choosing a cooperative partner, people could select a mother/father who will invest a lot of energy, time and resources to take care of their children. Because parental investment (from both parents) is a crucial resource, reproduction with a cooperative mate who invests in offspring is likely to be beneficial.”

Setting the mood

People also assortatively mate for personality traits. “We found the best evidence that couples are alike for extroversion: Being sociable, friendly and approachable,” Little says. “We also found positive correlations between couples for confidence, conscientiousness and having a broad range of interests.”

The reverse is also true: Some studies have found that couples assortatively mate for conditions like depression, anxiety and ADHD. “The more severe the symptoms are, the stronger the assortative mating,” Abdellaoui says. “We’re not sure yet why. Perhaps they have a stronger bond because they’ve shared similar stressful experiences.”

The happiness factor

If you share many similarities with your partner, rejoice: Some research has shown that the more you have in common, the more likely you are to stay together. “In a cross-sample of the population, relationship length was positively correlated with similarity,” Little says. “There is research suggesting that couples are less likely to stick together if they are dissimilar. People who stay together are the most similar.” (These are the most surprising secrets from the happiest couples.)

Lot Geels has found that the traits and qualities that she and her husband share have helped them to forge a deep bond. “I think that definitely makes things easier,” she says. “We don’t disagree on important things in life.”

There’s no recipe to ensure a blissful union yet: Researchers haven’t found that the presence or absence of any specific characteristics improves relationship quality. “We are not even close to being able to predict the success of your relationship,” Abdellaoui says. “I would not dare to advise someone on partner choice on what we know, especially genetics-wise. Just follow your heart.”

Originally Published in Reader's Digest International Edition