Fair enough. My bad.
The abstract for that paper clearly identifies the primary correlation with skin pigmentation as UV levels; furthermore the conclusion continues the same premise. Pages 72 and 73 identify the alternative reason for how both native Greenlanders and the Inuit maintain a darker skin tone in such northern climates (maintain, not develop) in the high degree of Vitamin D available in their diet. Therefore, if a fair-skinned population were to move north, there would be no overriding pressure to increase pigmentation, and thus they would retain a pale skin-tone. i.e. a darker skintone moving north is the baseline taken when assessing changes in relative melanin content in humans; increased Vitamin D in the diet would not have the same effect.
Otherwise, the mass domestication of chickens would have had a really strange effect by now.
I'm sorry, it's just that I do have a clear, fleshed-out setting here. It's a personal work for me as well as something I think works well in RPs: When you have an established setting you know what's possible and you know what can happen. I want to keep the rules consistent and I want to keep the races consistent.
That's why I want people to ask questions and please wait for my full response. Even when I don't have something completely fleshed out at the very least I can provide a general idea of it.
Not a good reason to be undead, no. Particularly as undead might not look undead but it wouldn't take months to realise "wait, I don't need food or rest".