In this environment of perpetual darkness, the eyes of [the ancestors of blind cavefish (Astyanax mexicanus)] were of little use and as generations passed, they disappeared entirely. They now navigate through the pitch-blackness by using their lateral lines to sense changes in water pressure.
But there is a deceptively simple way of restoring both the eyes and sight that evolution has taken, and Richard Borowsky from New York University’s Cave Biology Research Group has found it. You merely cross-bred fish from different caves.
So how does this work? Obviously the lack of eye development is the result of different mutations in different caves. In different caves, different gene mutations resulted in the loss of eyes.