"At some point back in deep time, a group of fish were washed into a limestone cave somewhere in northeastern Mexico," reports the Guardian. "With no way out and little more than bat droppings to eat, the fish began to adapt to their new troglodytic lifestyle. Unable to see other members of their group in the dark, they lost their colourful pigmentation. Then they lost their eyesight, their eyes gradually got smaller, and then disappeared altogether.This was accompanied by a dramatic reduction in the size of the brain’s visual system." Read more.