Illustration by Lia Kantrowitz
Social psychologists explain why two people in a couple are often more alike than one would expect by chance.
In honor of Valentine's Day, we're spending the week debunking myths and lies about romance. Read the rest of our "Love is a Hoax" coverage here.
Despite how catchy Paula Abdul's 1987 hit song "Opposites Attract" was back in the day, there's actually very little scientific literature to support the claim that people with completely different personalities fare better romantically. In fact, although it may feel a little grimey to want to hook up with someone who looks like they could be related to you, it's quite normal to be attracted to someone with similar attributes.
Anthony Little is a psychology professor at the University of Bath in the UK with expertise in face perception, mate choice, and social cognition. He says there's a lot of evidence to support assortative mating, or the notion that two people in a couple are more alike than one would expect by chance. "In fact, this is a common pattern seen in other animals too," he tells Broadly. "In humans, some of the strongest similarities between couples appear to be in social variables, such as in religious and political views and also in factors such as education, intelligence, and personality. Couples also match for lots of physical traits, most notably height and weight."
Social psychologist Robert Zajonc was one of the first people to look at physical similarities in couples based on faces. In a 1987 study, he and his colleagues at the University of Michigan recruited 110 undergraduates to analyze individual, black-and-white portrait photos of 12 married couples—one pair of photos from when they were first married and a second set taken 25 years later. Ultimately, participants determined the spouses pictured in the older photos were more similar in appearance and judged them more likely to be married to each other.
Read more: Why Men Fall in Love Faster Than Women
To explain the phenomenon, Zajonc pointed to empathy. "In marriage, the partners typically remain in the same immediate environment and, because of the nature of their relationship, empathize with a variety of their spouses' emotional states," he wrote. "Over time, therefore, these various emotional states are shared, albeit in reduced intensity, such that a substantial proportion of the emotions of the wife are also experienced by the husband, and vice versa. ... If the facial musculature plays a significant role in producing these emotional states and moods, then, with time, married partners should grow to resemble each other physically."
Or, as Little puts more simply, "sharing life's emotional experience could also cause couples' faces to appear more alike over time as they laugh, or cry, together."
Another theory for why some couples could be mistaken for siblings (think Justin Timberlake and Jessica Biel and Tom Brady and Gisele Bundchen) is the idea that people prefer someone who looks similar to themselves. In a 2002 study, Little and his co-researchers looked into this more closely, focusing (in somewhat of a Freudian way) on whether people are attracted to physical traits they see in their opposite-sex parents. Almost 700 participants were asked about their own, ideal, partner, and family hair and eye color characteristics, in addition to other questions about themselves, such as sex, age, and ideal sex of partner. Ultimately, Little discovered that "individuals choose partners that resemble their opposite-sex parent over and above any effects of own or same-sex parent effects."
"It is, however, well established that people generally respond positively to familiar stimuli and parental traits may be very salient familiar features," the study states. "Individuals may choose partners who possess similar [hair and eye] colour traits to their parents because they initially appear more familiar than prospective mates with different colour traits."
sharing life's emotional experience could also cause couples' faces to appear more alike over time as they laugh, or cry, together.
"We do like what is familiar," Little explains. "For example, the more times you hear a piece of music, the more positive you feel towards it. The same is true of abstract art—more familiarity means increased liking."
Or maybe we end up with look-alike partners because it's simply in our genes. A 2014 study from the University of Colorado Boulder found that people are more likely to choose a spouse with similar DNA. The role genetics plays in mate choice is small—about a third of the magnitude of education level, a more thoroughly studied trait—but when researchers analyzed the genomes of 825 white American couples, they found spouses displayed fewer differences in DNA than when compared to two randomly selected individuals.
At the same time, scientists have also identified other ways in which opposites attract. A 2009 survey found that people were more attracted to those who have dissimilar immunity genes from their own, which scientists believed would help people find mates that would allow them to reproduce to have healthier offspring.
But whether DNA similarities between lovers come from a lifetime of growing together or some unconscious preference, Little says there may be some benefits to pairing up with someone who resembles you. "Someone who looks like you might behave like you," he says, "and so partners who look alike may be more compatible. There is evidence, for example, that couples who are dissimilar are more likely to break up than those who are more similar. It is easy to imagine that there would be conflicts in a relationship if there are large differences in personality."
"Another idea," he continues, "is that similarity might have genetic benefits. Normally you are related 50 percent to your children, but if a similar partner shares genes in common with then you may have children who have more than 50 percent of their genes in common with you. In other words, pairing with someone similar might increase the number of genes you leave in the next generation."
Historically, the idea of people, in particular blond-haired, blue-eyed white men and women, pairing up in the interest of the gene pool hasn't gone over very well (think Hitler). "Genetic ideas of favoring kin has been misused by some groups," Little says. "At one level it is not controversial—I think people are fine with the idea that people favor their relatives over strangers because they have more genetic material in common. At its extreme, the idea can be misused to justify discrimination of minority groups because of their dissimilarity to the majority."
But, he continues, this is different. "This is about individuals, not groups."
Of course, partners who look alike and potentially have similar genetic makeup may want to keep one thing in mind. "Too much similarity would cause inbreeding," Little says, "so there may be a limit to how similar partners should be."
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