Two parts:
First, they're not exposing their skin to the sun. There's no reason to have paler skin to get more UV if it's covered up most of the year.
Secondly, for the Inuit diet there are parts that are very Vitamin D rich... and there are still problems.
Vitamin D-rich marine Inuit diet and markers of inflammation – a population-based survey in Greenland https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4709837/
> The traditional Inuit diet in Greenland consists mainly of fish and marine mammals, rich in vitamin D. Vitamin D has anti-inflammatory capacity but markers of inflammation have been found to be high in Inuit living on a marine diet
Vitamin D deficiency among northern Native Peoples: a real or apparent problem? - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3417586/
> Vitamin D deficiency seems to be common among northern Native peoples, notably Inuit and Amerindians. It has usually been attributed to: (1) higher latitudes that prevent vitamin D synthesis most of the year; (2) darker skin that blocks solar UVB; and (3) fewer dietary sources of vitamin D. Although vitamin D levels are clearly lower among northern Natives, it is less clear that these lower levels indicate a deficiency. The above factors predate European contact, yet pre-Columbian skeletons show few signs of rickets—the most visible sign of vitamin D deficiency. Furthermore, because northern Natives have long inhabited high latitudes, natural selection should have progressively reduced their vitamin D requirements. There is in fact evidence that the Inuit have compensated for decreased production of vitamin D through increased conversion to its most active form and through receptors that bind more effectively. Thus, when diagnosing vitamin D deficiency in these populations, we should not use norms that were originally developed for European-descended populations who produce this vitamin more easily and have adapted accordingly.
Vitamin D intake by Indigenous Peoples in the Canadian Arctic - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10260879/
> Vitamin D is an especially fascinating nutrient to study in people living in northern latitudes, where sun exposure is limited from nearly all day in summer to virtually no direct sun exposure in winter. This essential nutrient is naturally available from synthesis in the skin through the action of UVB solar rays or from a few natural sources such as fish fats. Vitamin D is responsible for enhancing many physiological processes related to maintaining Ca and P homeostasis, as well as for diverse hormone functions that are not completely understood.
do you suppose the traditional scandinavian diet is also lower in vitamin d? or is their apparent selection for blondness just a result of genetically higher vitamin d needs?
I am inclined to believe that genetic changes within the Inuit reduce vitamin D needs, the modern Scandinavian diet differs from a historical one, the oceanic climate of Scandinavia is warmer than the inland climate of North America (compare Yellowknife 62° N with Rana at 66° N and Tromsø at 69° N https://en.wikipedia.org/wiki/Subarctic_climate ) so that more skin can be non-fatally exposed...
And the combination of this had more skin exposed for better vitamin D production in Scandinavia and so the pressure was for lighter skin while the diet of the Inuit meant that that pressure for skin tone wasn't selected for.
... And I'll 100% defer to someone else with a better understanding of the genetics and dietitian aspects.
okay, now i'm just waiting for the study that shows that scandinavians are on average actually genetically 20% arabic and 20% west african, it's just that for centuries nobody suspected because they were so pointlessly obsessed with skin color ;)
The populations for North America were from an asian branch of the human migrations and so started with darker skins. The larger change to skin tone combined with less pressure (from diet) and the "it isn't that viable to shift to a less melanistic skin tone".
https://en.wikipedia.org/wiki/Paleo-Indians https://en.wikipedia.org/wiki/Peopling_of_the_Americas and https://commons.wikimedia.org/wiki/File:Early_migrations_mer...
This compares to a relatively more recent (12000 years - twice the age of the pyramids rather than four times the age of the pyramids for 25000 years ago) migration from Europe into Scandinavia ( https://en.wikipedia.org/wiki/Nordic_Stone_Age ).
> The Nordic Stone Age refers to the Stone Age of Scandinavia. During the Weichselian glaciation (115,000 – 11,700 years ago), almost all of Scandinavia was buried beneath a thick permanent ice cover, thus, the Stone Age came rather late to this region. As the climate slowly warmed up by the end of the ice age, nomadic hunters from central Europe sporadically visited the region. However, it was not until around 12,000 BCE that permanent, but nomadic, habitation in the region took root.
> Around 11,400 BCE, the Bromme culture emerged in Southern Scandinavia. This was a more rapidly warming era providing opportunity for other substantial hunting game animals than the ubiquitous reindeer. As former hunter-gather cultures, the Bromme culture was still largely dependent on reindeer and lived a nomadic life, but their camps diversified significantly and they were the first people to settle Southern Scandinavia (and the Southern Baltic area) on a permanent, yet still nomadic, basis.
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https://en.wikipedia.org/wiki/Genetic_history_of_the_Indigen...
https://en.wikipedia.org/wiki/Haplogroup_Q-M242
The population that migrated to North America 25000 years ago may have been darker skinned than the European branch of human migration where a lighter skin tone developed. This, combined with later genetic isolation (note we're talking about two continents - but this is isolated compared to the possible movement of genes within Europe and Scandinavia 12000 years ago and more recently) fixed the darker skin, and the adaptation for vitamin D in the Inuit population because of the lighter skin wasn't genetically advantageous and was a greater genetic distance from the population compared to the Scandinavian migrations which was followed by the Holocene climatic optimum https://en.wikipedia.org/wiki/Holocene_climatic_optimum with even more warming of Northern Europe resulting in a lighter skin tone being an easier genetic path for greater vitamin D during the summer months.
... And all of that is a just so story that I'd love to go and be a grad student working on the genetic diversity of early human migrations now to find out if it actually worked that way or if I'm just making things up.
Human skin pigmentation, migration and disease susceptibility - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3267121/
> Human skin pigmentation evolved as a compromise between the conflicting physiological demands of protection against the deleterious effects of ultraviolet radiation (UVR) and photosynthesis of UVB-dependent vitamin D3. Living under high UVR near the equator, ancestral Homo sapiens had skin rich in protective eumelanin. Dispersals outside of the tropics were associated with positive selection for depigmentation to maximize cutaneous biosynthesis of pre-vitamin D3 under low and highly seasonal UVB conditions. In recent centuries, migrations and high-speed transportation have brought many people into UVR regimes different from those experienced by their ancestors and, accordingly, exposed them to new disease risks. These have been increased by urbanization and changes in diet and lifestyle. Three examples—nutritional rickets, multiple sclerosis (MS) and cutaneous malignant melanoma (CMM)—are chosen to illustrate the serious health effects of mismatches between skin pigmentation and UVR.
Also of interest - The colours of humanity: the evolution of pigmentation in the human lineage https://royalsocietypublishing.org/doi/10.1098/rstb.2016.034...
The different pathways for depigmentation are different.
> The fact that depigmented skin evolved independently in the ancestors of modern Europeans and East Asians suggests that at least two (and probably more) distinct genetic mutation events occurred and that multiple loci underwent positive selection in these two regions receiving relatively low levels of UVB. The most likely reason for this was that it was associated with a loss of skin pigment that favoured vitamin D production under conditions of low UVB.
however, the downvotes on my comment upthread are making it clear that this is not the kind of place where it's safe to discuss questions like whether the selective pressure for more melanin from sunburns is stronger or weaker than the selective pressure for less melanin from rickets
the viking ones might even be historically accurate (if biased); not only did vikings recruit new warriors from abroad, they also enslaved concubines from abroad, and their raiding reached not only greenland (inhabited by inuit peoples) and north america (rarely!) but also the mediterranean. so it wouldn't be terribly surprising for a viking warrior a thousand years ago to have a great-grandmother who was kidnapped or bought from morocco, greenland, al-andalus, or baghdad. and of course many sami are olive-skinned, and viking contact with sami was continuous
the vitamin-d-deprived winters of scandinavia are not kind to dark-skinned people (how do the inuit do it? perhaps their diet has enough vitamin d even without sun?), but those genes won't die out in a generation or two, even if 50 generations later there isn't much melanin left
a recent paper on this topic with disappointingly sketchy results is https://www.duo.uio.no/handle/10852/83989