For Tatiana Giraud, cheese isn’t just an emblem of French cuisine—it’s a complex and evolving world of microorganisms.

So when Giraud, a microbiologist at the French National Center for Scientific Research, stocked her lab’s fridge with wheels, wedges, and rounds of cheese ordered online, it wasn’t just to spread globs of the dairy product on crackers. (But rest assured: “We took all the samples we needed,” Giraud says, “and then we ate the remaining.”).

Instead, Giraud and her colleagues were looking for traces of evolution in the molds that make up Camembert’s rind, and that marble Roquefort with blue streaks. And they found something surprising: These distantly-related species of fungi have somehow recently swapped chunks of