Male Japanese quails seeking the attention of females need to do just one thing: Hang out with other female Japanese quails.

The same trick works for sailfin mollies.

If females in this fish species see a male drawing the attention of other females, researchers say, they’ll offer their attention too. In essence, these fish seem to be thinking if other females find certain males attractive, there must be a good reason—and so they’ll follow suit.

“What this suggests,” says Robert Kurzban, a Penn assistant professor of psychology, “is that the females are more interested in spending quality time with the males who are spending quality time with other females in their species.”

The phenomenon is known as “mate copying.” And recently, Kurzban set out to determine, for the first time, whether humans engage in the behavior, too. Kurzban explained his findings—which he described as somewhat surprising—during a recent Penn Science Café event at MarBar.

Kurzban’s experiment was simple: Taking a cue from web sites such as hotornot.com, he showed 98 Penn undergrads a series of slides that paired together men and women of varying attractiveness. Then he gathered information on how attractive the surveyed undergrads found people shown in the slides.

When men or women were paired up with attractive opposites, Kurzban said, survey participants found them more attractive. The inference, then, is that humans—both men and women—are more likely to want to have sex with, or be in a relationship with, people who are dating other attractive people. “The bottom line is, the more attractive the person you’re dating, the more desirable you are in the context of sex and relationship,” Kurzban said.

The human version of mate copying is slightly different than other species, however. For animals, mate copying takes place in a “one-sided market”—that is, for female Japanese quails, simply knowing that other females find a male attractive is information enough.

Among humans, Kurzban said, it’s also important for women to know which women find that male attractive. This is called a “two-sided market”—and it helps explain, Kurzban says, why movie stars end up with movie stars.

“There’s no nice to way to say this, so I’ll just say it,” Kurzban joked, “The 10s usually end up with the 10s.”