Time and again, whenever a population was swept into a cave and survived long enough for natural selection to have its way, the eyes disappeared. “But it’s not that everything has been lost in cavefish,” says geneticist Jaya Krishnan of the Oklahoma Medical Research Foundation. “Many enhancements have also happened.”

Though the demise of their eyes continues to fascinate biologists, in recent years, attention has shifted to other intriguing aspects of cavefish biology. It has become increasingly clear that they haven’t just lost sight but also gained many adaptations that help them to thrive in their cave environment, including some that may hold clues to treatments for obesity and diabetes in people.

Casting off expensive eyes

It has long been debated why the eyes were lost. Some

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