I thought that too but then why did Mongolians who also moved into colder climates not develop as such.
There are flaws in the climate and topography rationales....though they do seem ...rational.
not meaning to argue...i do not know the answers but neither do I think science does and in this arena it is so politicized that it's hard to wonder
I am not convinced all humans evolved at the same time from the precise source except Biblically.
Now that we know other near HomoSapiens actually overlapped.
Northern Asians seem to have more oily skin, American Indians rubbed bear greese on their skin. These acts would enhance Vitamin D formation. Coastal Esquimos eat a lot of fish, including the liver which is very high in Vitamin D, as to Scandinavian people. Many primative peoples eat animal livers with great enthusiasm. Perhaps all liver is somewhat higher in Vitamin D, in addition to being highly nutritious.
Incidently, if you want to get more Vitamin D in the winter, bathe late in the evening so you have oil on your skin when you go out in the morning, and several hours to absorb the Vitamin D after you come in. There may be a correlation between Vitamin D levels and winter depression. More would be good.