Weather forecasters predict that temperatures will be several degrees below freezing in the capital city of Greenland, Nuuk, for the rest of this year. While many of us would huddle indoors under such weather conditions, Inuit in the iceberg capital of the world will continue to go about their business with barely a shiver.
It turns out that they, along with Native Americans and some Siberians, possess a unique gene variant associated with cold tolerance, according to a paper published in Molecular Biology and Evolution. This variant is a close, but not exact, match to a gene sequence found in Denisovans, which are extinct humans who once ranged from Siberia to Southeast Asia.
People with the variant today, however, live in places at or near where Neanderthals once were. This means that Native Americans, Inuits and certain Siberians are all related to Denisovans, to Neanderthals (perhaps more so than the rest of us with European and/or Asian heritage), or to an as-of-yet unidentified extinct human ancestor.
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The gene variant is "almost absent in Africa, which is one of the reasons why we think the variant was introduced from archaic humans living in Eurasia," lead author Fernando Racimo of the New York Genome Center told Seeker.
Racimo, who was a graduate student at UC Berkeley at the time of the study, and his team compared genetic data from nearly 200 Greenland Inuit to people tracked in the 1000 Genomes Project and to ancient human DNA from Neanderthals and Denisovans. The other known archaic human from outside of Africa-the Hobbit (Homo floresiensis)-wasn't included in the study because there is no complete Hobbit genome yet.
The comparison put a spotlight on the region of the genome containing two genes: TBX15 and WARS2. This is where the variant possessed by the cold-tolerating people lies. Racimo explained that it is thought to cause a certain type of body fat commonly known as "brown fat" to generate heat.
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He continued, "The gene is also involved in a number of other traits, like body fat distribution, bone and facial morphology (structure)."
The discovery marks only the second major finding that ancient interbreeding conferred useful traits to modern humans. The first was the discovery that Tibetans have a very beneficial gene variant, likely inherited from Denisovans. It allows them to use oxygen efficiently when the air is thin at high altitudes.
The authors speculate that the Native American, Inuit and Siberian gene variant could be part of early American history. That's because the people who expanded throughout Siberia and across Beringia-the former land bridge connecting what are now Russia and Alaska-and into the Americas all likely had the special genetic adaption for cold tolerance.
As Racimo said, "perhaps as modern humans were expanding across Beringia, it might have been useful to have this variant."
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