Why do some salamanders lose the ability to see as adults?

In dark habitats such as caves, vision offers little survival benefit, so natural selection may favor traits that improve touch, smell, or vibration sensing instead. Several salamander species, including cave-adapted forms, have very small eyes or eyes covered by skin. This is not because eyes suddenly stop working, but because generations of living in darkness make large, energy-costly eyes less necessary. Similar changes have evolved independently in many cave animals, a classic example of convergent evolution. The result is often a trade-off: less vision, but better adaptation to a lightless environment.