An article, which you can read here Arctic Inuit, Native American cold adaptations may originate from extinct hominids from Dec. 2016, tells us something about the Inuit, Amerindians and Denisovans or some other now extinct archaic hominid... (the original paper is here).
Two genes, TBX15 and WARS2 seem to be critical in how the body deals with fat in cold climates to generat heat. The article points out the following:
" The Inuit DNA sequence in this region matches very well with the Denisovan genome, and it is highly differentiated from other present-day human sequences, though we can't discard the possibility that the variant was introduced from another archaic group whose genomes we haven't sampled yet," said Fernando Racimo, lead author of the study.
The authors found that the variant is present at low-to-intermediate frequencies throughout Eurasia, and at especially high frequencies in the Inuits and Native American populations, but almost absent in Africa. TBX15 is a gene known to affect the human body's response to cold, and is associated with a number of traits related to body fat distribution. The authors speculate that the archaic variant may have been beneficial to modern humans during their expansion throughout Siberia and across Beringia, into the Americas."
Allow me to suggest another option: the archaic variant evolved in Homo erectus in high latitude Asia, they had reached this part of the world at least 1 million years ago. They hunted big game (mammoths and hairy rhino lived there and did so for millions of years). What would stop them from following the heards into America? Thanks to this adaptation they could. And this is why, their descent, the Amerindians carry it. Later after Homo sapiens evolved in America, it back migrated into Siberia and Eurasia and reached -though diluted- Africa when it was peopled by modern H. sapiens from Asia and America.
This explains the cline from a peak in America to a low in Africa. As you moved into hotter regions it became less of an advantadge (actualy a fatty layer in a hot climate is a disadvantage).
Archaic Adaptive Introgression in TBX15/WARS2 Fernando Racimo David Gokhman Matteo Fumagalli Amy Ko Torben Hansen Ida Moltke Anders Albrechtsen Liran Carmel Emilia Huerta-Sánchez Rasmus Nielsen Mol Biol Evol (2017) 34 (3): 509-524. DOI: https://doi.org/10.1093/molbev/msw283 Published: 22 December 2016
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