A Chicago researcher says he’s found insight into how ecosystems work from what may be the world’s most basic game: rock, paper, scissors.

Stefano Allesina says there’s long been a paradox in ecology. An ecosystem can teem with thousands of competing species, but the math can’t quite explain that. Models suggest that more strong ones should push out more weak ones, leaving fewer species overall.

Now Allesina says he’s worked out a new model to account for the diversity. The key was finding a setting where multiple, equally powerful contestants can all survive: rock, paper, scissors.

“For any two species, you have one winner, and it’s a very clear winner,” says Allesina, an assistant professor of ecology and evolution at the University of Chicago. “But through a third species, they can close this cycle, and then start this mechanism.”

Allesina scaled up the game to not just three variables, but hundreds or thousands. He says his model could account for almost unlimited biodiversity, and it also explains why why the loss of one seemingly minor species can topple a carefully balanced ecosystem.

His findings are out in the Proceedings of the National Academy of Sciences.