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Surely it has more to do with lighting levels than anything. And if you add the fact one persons comment that "blue eyed people produce more vitamin D". Well it is due to lower light levels and as we know we require vitamin D to also prevent depression So maybe the same the same switch that control vitamin D production influences melanin production. Northerners do not require as much melanin anyway to protect us from the sun however we still need to produce the same amount of vitamin D from lower lighting levels.

So obvious......

Matt
Edinburgh, Scotland