Chris Kaelin, a geneticist at Stanford Medicine, found himself thinking about cats. Not just any cats, but the loud, lovable, and often male ones streaked in unmistakable marmalade. These orange felines — icons of internet memes and cozy laps — have baffled scientists for over a century.

Scientists have confirmed that there is something unique about ginger-hued domestic felines. In a new study, Stanford Medicine researchers have discovered the long-posited but elusive genetic mutation that makes orange cats orange—and it appears to occur in no other mammal.