Nighttrain writes:
Do retained mutations give us clues to past environmental conditions? The redhead gene supposedly provided increased amounts of vitamin D from sunlight. Did it arise from a post-impact climate with reduced light?
It's more common in Scotland and Ireland than anywhere else I've been, and history tells us that the Scots and Irish have a higher percentage of their ancestry that would've been on these very cloudy islands for a very long time than the English do.
Because of the gulf stream effect, it may be that we actually get less direct sunlight than pretty much anywhere else in the world. The red hair seems to be a byproduct of genes that also produce very pale skin, an advantage in this climate for absorbing vitamin D, but definitely vestigial for those redheads who've ended up in Australia, where your linked article came from. In fact, like the appendix, actually disadvantageous in a sunny climate.
So, although I think your post-impact hypothesis is an interesting one (and it would make sense) I think that the answer to selection for redheadedness may lie in our dull, cloudy climate, and it may be just a bit of local micro-evolution that pushed further across the population on Britain and Ireland than anywhere else.
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