The soft, blinking lights of fireflies aren’t just beautiful—they may also play a role in creating new species. A new study shows that using light-up powers for courtship makes species split off from each other at a faster pace, providing some of the clearest evidence yet that the struggle to find mates shapes the diversity of life.

The firefly’s glow, like the enormous claws of fiddler crabs and the elaborate dances of manakins, was sculpted by the struggle for sex. Scientists have long thought that this kind of mating-driven natural selection—called “sexual selection”—could make species split into two. Say females in two populations prefer different color patterns in males: Even if the populations have the same needs in every other way, that simple preference could make them split into species with males of separate colors. “A lot of closely related species differ in sexual traits,” says Emily Ellis, an evolutionary biologist at the University of California (UC), Santa Barbara.