There's Something Disturbing About the People We End Up With

Popular wisdom tells us that opposites attract. But take a look around you and bear witness to the thousands of "couple twins," "boyfriend twins," celebrity couple lookalikes and even facial recognition dating sites, and you'll start to realize that what we might be most attracted to is, well, ourselves.

It's no mistake: We end up with people who look like us.

Don't get too freaked out when you realize your boyfriend has that same square jaw, or your girlfriend is also a brunette with killer dimples, or that everyone always mistakes you for siblings. Science can explain why so many of us end up dating and marrying people who resemble us. 

We're attracted to familiarity.

Think about it: We're comfortable with what we know, and what we know best is our own face. "When you have a face that looks more like you, you tend to trust it more and think it looks more cooperative," Tony Little, a research fellow in psychology at the University of Stirling in Scotland told USA Today. 

That attraction to familiarity shows in the numbers. Statistician Emma Pierson studied 1 million matches made by dating site eHarmony's algorithm and found that people are overwhelmingly interested in people like them. When it came to traits like height and attractiveness, people who displayed a certain trait prefer people who also displayed that trait, and they preferred it more strongly than people who don't. 

Everyone likes hot, fit people — but hot, fit people themselves display a stronger preference for other hot, fit people. The same goes for tall people, as Pierson explained on FiveThirtyEight: "All women prefer taller men, but tall women display a stronger preference for tall men." 

Science supports the eHarmony patterns: Research published in the Personality and Social Psychology Bulletin in 2010 noted that brains process familiar images more easily. (In fact, we are so fond of familiarity that a 1985 study of married couple's names found that there's a 12% likelihood above chance that a couple will have alliterative names. Kim Kardashian and Kanye West now make complete sense.)

We're attracted to our genes.

It's not just familiarity. When it comes to attraction, we're a little more narcissistic than we'd like to admit. The 2010 study in Personality and Social Psychology Bulletin asked participants to rate the general sexual attractiveness of strangers. When photos of the strangers were morphed with the participants' faces (up to 45%), subjects found the photograph blended with their own face to be the most attractive of all. 

The same held true when subjects were exposed to an image of their opposite-sex parent right before the stranger's photograph, but only if the subjects weren't aware of the exposure. The key finding: People who remind us of ourselves or our parents are more attractive to us (but only if that resemblance is unconscious — phew). 

Previous studies have shown that heterosexual couples often partner with people with similar DNA structures. Another study from the University of Western Ontario found that identical twins took the similarity of their mate selection one step further: Not only did identical twins look like their chosen partners, but the non-related spouses of the twins often resembled one another very closely. 

Our personalities are written on our faces.

We may actually end up with doppelganger partners because we're seeking people with similar personalities, and we read each other's personalities from each other's faces. As reported by LiveScience, face shape and brow structure are just two physical features that can influence our perceptions of people upon first meeting. For example, higher levels of testosterone are related to masculine face shapes like prominent chins as well as "masculine" personality traits like dominance. Smiles and eyes also often determine how we feel about a person: They're aggressive, charming, playful or depressed. 

"Smiles are important social cues that may tell us whether or not someone is friendly and eyes are also a traditional focus of attention," Little told LiveScience. 

Sure enough, a 2005 study had participants rate 85 married couples' faces for perceived personality traits, going on the premise that "choosing a partner on the basis of similar personality could lead to facial similarity in partners in terms of apparent personality." The conclusion? "Matching was found for several perceived personality traits." 

While it might not always be fair to judge (hello, bitchy resting face), we tend to look for personalities similar to our own in other people's faces. 

We actually grow to look alike.

Ever notice how older couples tend to look eerily similar? That's because the longer a couple is together, the more their looks actually seem to merge.

University of Michigan psychologist Robert Zajonc analyzed photographs of couples taken as newlyweds and compared them to portraits taken 25 years later, asking participants to match photographs according to facial similarities. The results showed that while young couples weren't always facially similar, more participants thought the couples looked alike later in the relationship. 

While a lifetime of common diets certainly can contribute to older couples resembling one another, shared experiences also impact how we look. People who live together often empathetically mimic the facial expressions of those around them unconsciously. Couples might also share the same kind of emotional highs and lows throughout the years (family deaths, financial worries, the joys of parenting).

Over time, these expressions can shape facial musculature and wrinkles. So the longer you're with someone, the more your shared life can alter how you both look. If they have laugh lines, you might too. If you have crow's feet around your eyes, your partner probably does. The body is a spooky and wonderful thing.

Lookalikes may be happier in the long run.

While experimenting with diversity when you're dating can be wonderful, entering relationships with people who resemble you isn't necessarily a bad choice. Another key finding of Zajonc's study was that couples who reported more happiness in their relationships tended to have greater facial similarities. In other words, looking alike might be the result of a happier, more fulfilling relationship.

How we feel about our partner's face might even contribute to how we feel about others. In fact, some studies have shown how our preference for our significant other's face can lead us to treat people who share similar facial features in a similar manner via transference. If we're happy with our partners, there's a good chance we will be friendlier to faces that resemble theirs (and in turn, our own). 

The science of couple doppelgängers reveals a lot about our own biases in the world, but it can also give us some reassurance. While others might claim you're just dating people who look like your siblings, you're really just weeding out mates for the happiest, healthiest potential. You can't help it if they're just as good looking as you.