Those folks haven't been there very long. They still retain the general skin color of their Siberian ancestors. The skin color changes throughout the Americas are (or were) a "work in progress" as these things generally take time.
You imply that, generally, dark skinned people in the north should have health problems due to lack of vitamin D deficiency.
Modern groups have vitamin D fortified milk (that's the reason its there!). Groups in the far north supplement their diets with fish oils. They live too far north to get any appreciable vitamin D from the sun, and they can't expose their skin to the sun for very long anyway, lest it freeze.
I've never heard such a thing.
That means nothing. Try reading some books on human races.
Plus I have never heard of light-skinned persons, generally, having health problems due to excessive vitamin D production at the equator.
The problem for light-skinned people at the equator is not excessive vitamin D production, it is cancer caused by excessive ultraviolet radiation reaching the lower skin layers. That is why the skin needs to be dark. Of course, modern light-skinned folks can avoid this problem (and sunburn) by wearing clothes, hats and using sun screens.
So I reject your explanation of the "improvement". You don't even try a just-so story for the DNA sequence improved upon.
Reject away. But until you learn something about the subject, your rejection means nothing.
Really, I have 20-30 books on human races and closely related topics at the office. I would be happy to provide some titles.
And vitamin D is a basis of your argument for "improvement". You now support evidence counter to your argument.
P.S. Siberia is not equatorial either.
Reject away. But until you learn something about the subject, your rejection means nothing.
Well fine since you answered me, I think in an attempt to answer my question, and failed to convince me. I told you why. Just-so stories don't hack it.
Modern groups have vitamin D fortified milk (that's the reason its there!). Groups in the far north supplement their diets with fish oils. They live too far north to get any appreciable vitamin D from the sun, and they can't expose their skin to the sun for very long anyway, lest it freeze.
Concerning vitamin D Vitamin D Deficiency Study Raises New Questions About Disease And Supplements
ScienceDaily (Jan. 27, 2008) — Low blood levels of vitamin D have long been associated with disease, and the assumption has been that vitamin D supplements may protect against disease. However, this new research demonstrates that ingested vitamin D is immunosuppressive and that low blood levels of vitamin D may be actually a result of the disease process. Supplementation may make the disease worse.
...
"Our disease model has shown us why low levels of vitamin D are observed in association with major and chronic illness," Marshall added. "Vitamin D is a secosteroid hormone, and the body regulates the production of all it needs. In fact, the use of supplements can be harmful, because they suppress the immune system so that the body cannot fight disease and infection effectively."