the Darwin fish

On bonerici:

Red haired people are like the blind fish in caves, who have lost their sight because they no longer use it.

A more recent hypothesis is that they've lost their sight because there's selection pressure to produce more of that Hedgehog protein you mentioned. The positive effects on their taste buds and tooth development may outweigh the negative effects on their sight when their sight isn't needed. Carl Zimmer explains it.

I link to it because it's humbling for evolutionists to think they were taken in for so long by the plausible-sounding "disuse" hypothesis (which is really Lamarckian). But even more so, it's credibility-enhancing for evolutionists that they eventually got past that and other just-so stories and found a real, scientific explanation for this evolutionary change. This is how we know they're not dogmatists who make up explanations like "redheads must get more Vitamin D" just to make everything fit into their world view.