So I get the fact that skin color is largely an evolutionary response to avoid the effects of harsh sunlight at more equatorial latitudes and the need to produce more vitamin D at more arctic latitudes but ISTM that light skin color absorbs less light than fark skin color. Shouldn’t Northern Europeans have darker skin to absorb more sunlight and the Africans have lighter skin to reflect sunlight? I’m sure there is an simple easy answer.
I don’t think it’s attributable to heat regulation, it’s because melanin is protective against solar UV.
ETA: per Wiki, it may be lability of folate under UV rather than just melanoma risk.
UV penetrates the skin to (eventually) help form Vitamin D. Melanin blocks the entry of UV. At a latitude with little sun, people have less melanin to let more sunlight/UV in. In bright-sun areas, they have more melanin to block the UV - I’d assume to keep Vitamin D production from being excessive.
All I know for sure is that here in Nwingland, most people over 40 or so who don’t drink a lot of milk and eat dairy products have to take Vitamin D supplements. I assume the problem is more pronounced for those with darker skin.
As said, dark skin is caused by melanin which protects against ultraviolet and importantly, melanin works by* absorbing* light rather than reflecting it. Therefore, human skin adapted to strong sunlight is brown-to-black. And even that is almost a side effect; we can’t actually see ultraviolet, so it’s just luck that melanin happens to be dark in both visible light and UV.