I would also chip in pheomelanin, which can affect overall colouring from the hair, to the skin, to the eyes. When most people discuss melanin, they mean eumelanin.
Razib has talked about this – here’s what I think.
The various sweeping alleles that have made Europeans and North Asians have light skin were not favored because they helped you garner extra vitamin D, at least not mostly. This is apparent from the allelic structure. There is a single sweeping variant for SLC24A5: if paleness was the point, many partial loss-of-function alleles would be favored, rather like what we see with G6PD deficiency (a malaria defense). But there is only one: so loss of function is not the point (or at least not the sole point): that particular variant has some other advantage, a big one. The fact that it’s favored up on the Ethiopian plateau is another sign that it isn’t driven by vitamin D. There is only one blue-eye mutation (OCA2), only one main blond mutation (KITLG). The SLC24A5 mutation has by far the largest effect on…
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