Not long ago, a single friend of mine observed something about the photos that men post of themselves on Match.com and other sites. Many—too many for her taste—also include women. Ex-girlfriends, presumably, with their slender arms thrown around the men in question. Or possibly friends, but always attractive ones. Even when the woman in the photo had been cropped out, whatever body part remained in the frame was comely. Long blond hair. Manicured nails.

Why do so many singles post pictures of themselves with exes? Do they know, at least on a level, that having a gorgeous ex makes them look hotter?

It actually does, according to a matchmaking strategy called mate-choice copying. Birds do it, and so do many other animals. There's mounting evidence that humans are no exception. If a person has an attractive partner, then there must be something worthwhile about him or her that may not meet the eye. It’s a -of-crowds approach.

In a recent mate-copying study, researchers at Duke University and the University of California at Davis asked a group of straight volunteers to rate the of men and women who were photographed solo. A second group of volunteers was asked to rate the attractiveness of the same men and women when paired with a person of the opposite . They were told that each couple had once been romantically involved but had broken up. How hot was the individual of the opposite sex? How much would they like to date that person?

Turns out, it depends on the ex.

Both male and female volunteers rated faces as more attractive, desirable, and dateable when paired with hot exes than when featured solo.



While having a hot ex is a boost to your attractivess, having a homely one can hurt you. When volunteers spent more time looking at a potential mate’s unattractive partner, they were less interested in that person.Take note: volunteers were only asked to rate people of the opposite sex, but they all spent significant time looking at each person’s partner.

There's an exception to this rule, and (as usual) it's hot women. While female volunteers downgraded otherwise hot men if they were paired with a dumpy partner, men gave high ratings to an attractive woman regardless of her partner's appearance. Women, generally the choosier and more cautious sex, are more likely than men to rely on social cues such as whether other women find the target guy attractive.

Is it really a good strategy to include a picture of yourself with an attractive ex-girlfriend or boyfriend (or a hot friend) in your dating profile? My exasperated friend would say no, yet all too often the guys that she finds exceptional are the ones who have hot exes.

*If you like this blog, click here for previous posts or follow me on Twitter. If you wish, check out my new book on what we don't expect when we're expecting: Do Chocolate Lovers Have Sweeter Babies?: The Surprising Science of Pregnancy.