When it’s time to find a mate, the female guppy (Poecilia reticulata) hunts for someone special. The value she places on rarity—specifically, in the shiny, colored marking on a male’s body—may drive the surprising diversity of guppy patterns in the wild, according to new research published online today in Nature. In the lab, female guppies have shown a preference for males with uncommon markings. Now, researchers have confirmed these results in the wild by fiddling with the ratio of different fin patterns among pools of the fish in Trinidad. They sorted wild males into two groups based on whether their tail fins were mostly transparent (like the guppies in the left column, above) or mostly colored (right), then reintroduced them into different breeding pools so that one fin type outnumbered the other three to one. They waited 16 to 17 days while females mated with their favorite males in the bunch, then scooped up these pregnant females to run paternity tests on their broods. Based on the first round of offspring (693 guppies in all), they found that a rare male sired more than twice as many guppies as a common one, no matter which pattern he bore. The evolutionary reason behind the effect isn’t clear, but it could be a way of avoiding inbreeding between genetically similar fish to create a more diverse population.