I know the nail bed contains no melanocytes giving the keratin it’s translucent appearance. I’m wondering if there is some evolutionary reason for this or if melanin would affect the nail’s functions or…
Thanks,
Kuroinukan
Well we know that melanin wouldn’t affect nail function, because chimpanzee fingernails are usually melanised and the same colour as the hair and they work just fine.
There is speculation that human palms and nails are white to provide a contrast with dark skin that allows easier communication via hand gestures. All people tend to have nails and palms about the same colour, regardless of skin colour, and in dark skinned people that provides a high contrast allowing hand gestures to be read easily at distance and under low light. Basically the idea is that light hands and nails provide the same function as eyebrows in aiding non-verbal communication.
Plausible, but like most evolutionary explanations for human traits, it’s a “Just So” story. There’s no real way of falsifying it and it may be equally true that it exists because there is no particular pressure against it.
It may also be significant that keratin, like melanin, blocks UV light from damaging lower levels of the skin. Therefore having melanin in areas that are already protected by keratin (the palms and soles of the feet have thicker keratin deposits than the rest of the skin) may simply be redundant.
That might explain why there is no selective pressure on fingernail or palm colour, but it doesn’t really explain why palms and nails became de-melanised to begin with. All the other apes have melanised palms and nails (AFAIK) and being forest creatures the melanin would be even more redundant than it is in humans. So simply being redundant can’t be the reason why the melanin was lost.