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A lot has changed in dating culture over the last few years. Take a gander at the New York Times wedding announcements, ie, the “sports section” for people invested in this season's lineup of urban-rustic nuptials. Increasingly, the pages that once featured a series of Southampton and grad-school meet-cutes are making room for "the couple met on Tinder in 2012.”

But one thing hasn’t changed much: our fascination with how and why we select romantic partners the way we do. The rise of digital dating means single people are making their own matches, rather than, say, relying on coupled-up friends for set-ups. This may not be a bad thing, as a new study suggests those with significant others may not have the same concept of "hot" as their single pals. Researchers from Charles University in Prague found that unattached people strongly prefer faces different from their own, whereas people in relationships are more likely to perceive people who look like them as foxy. Of course, the explanation is evolutionary: No one wants a date to end with the realization both people are talking about the same Aunt Esther. Once people are paired off, concerns of inbreeding lessen. 

For the study, published in Frontiers in Psychology, researchers ran two similar experiments in which Czech university students (mostly female) played hot-or-not — for science, of course. Basically, participants looked at pairs of composite photos (generated from real faces). In each case, one of the two facial composites was digitally manipulated to resemble the participant more than the other one was. Participants had to say which was more attractive (in the first experiment) and sexier (in the second).

Here's what they found: Uncoupled participants rated dissimilar faces as sexier than "self-resembling faces," whereas participants in relationships showed no preference in either direction. Single people, according to study authors, might be drawn to people who don't share their green eyes or left-side dimples as an adaptive defense against keeping it in the family.

But, once people are paired off, fear of incest no longer steers them towards dissimilar faces, explained study authors. Instead, it's in their interest to pay attention to faces that resemble theirs because family takes care of family. It's not that coupled-up people become sexually attracted to their look-alikes, but rather that they generally gravitate towards people with whom a relationship confers some evolutionary advantage. Single people need to dip into a new gene pool to keep the bloodline going. But, people who've found mates need to identify relatives, who will support them more than strangers will. 

The current study results both contradict and support previous work on mating preference. Despite the benefits of a diverse gene pool, plenty of studies have shown a desire for similarity among couples. For example, study authors mentioned research that showed people prefer faces of unfamiliar people with similar genetic makeups.

There's still a lot to iron out in the science of judging sexiness.

Other research offers additional differences in how single and non-single people perceive attractiveness of strangers. Romantically involved participants, for example, appear to spend less time checking out attractive people, and discriminate less between hotties and notties, than single participants. Along those lines, the current findings suggest that being in a twosome "reduces the perceptual preference for dissimilar faces" that one-somes have.

Though tangential to the main findings on relationship status, the study found that more attractive participants (as rated by a separate group of people) heavily preferred faces manipulated to resemble theirs, meaning faces made more beautiful. Homelier participants, on the other hand, favored faces manipulated to look less like theirs, which also translates to faces made more beautiful. So, regardless of whether someone was a sight for sore eyes or a sorry sight; scared of incest or looking for kin-folk to pay their debt, they were drawn to a beautiful face. 

Overall, the study highlights relationship status as another factor involved in perceptions of facial attractiveness. Across men and women, single people took a "different (than me) is beautiful" perspective. But, study authors noted limitations to flesh out, including their failure to explore qualities of participants' relationships. It's possible, they noted, "that the level of commitment or relationship satisfaction could influence preferences for self-resemblance." So, there's still a lot to iron out in the science of judging sexiness.