Comment by kragen
1 year ago
huh, that's a really interesting idea! the theory is that exposing skin to the sun is a cheaper way to get vitamin d than the inuit genetic adaptations, and so given the possibility of doing so, the scandinavians (and sami) experienced a strong genetic selective pressure for light skin which the inuit didn't?
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 Scandinavian and Sami were coming from the lighter skinned European populations and so didn't need as much change to become even lighter skinned.
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.
maybe! but there does seem to be a strong selective pressure for skin melanin from sunniness that operates over only a few millennia in at least some cases; consider indigenous australians and southern indians in addition to the neotenically blond scandinavians
I am inclined to believe that the pressure for more melanin (cancer, sunburns) is a more rapid adaptation than decreasing it.
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.
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