Arctic Inuits may have adapted to the cold and harsh climate thanks to genetic variants that first emerged in archaic humans, the Denisovans. These variants may protect them by generating a specific type of body fat and by changing their body fat distribution.
How Inuits have survived for so many years in some of the coldest regions of the globe – with a restricted seafood-based diet rich in protein and fatty acids but not in carbohydrates – is a question that has long intrigued scientists.
A study published in 2015 had conducted a first population genomic analysis of the Greenland Inuits, identifying regions of the genome that showed sign of an adaptation compared to other population groups.
At the time, the researchers had identified and studied mutations in a cluster of genes involved in the metabolism of unsaturated fatty acids. These mutations appeared to be an adaptation to the fact Inuits get a lot of fatty acid from their very specific diet. It allowed them to stay in good health despite mainly eating foods high in marine mammal fat.
But the scientists had also pinpointed another region of Inuits' genome on chromosome 1, containing two genes known as TBX15 and WARS2. Mutations in this region were thought to be central to the adaptation of Inuits to another component of their environment – the cold weather.
In the new study published in Molecular Biology and Evolution, the scientists decided to investigate these two gene variants further. In particular, they worked to trace back their origins.
Comparison with archaic humans
The scientists, led by Fernando Racimo from the New York Genome Center analysed genomic data belonging to nearly 200 Greenlandic Inuits. They compared this with data from the 1000 Genomes Project and with ancient hominid DNA from Neanderthals and Denisovans.
The scientists found that the Inuit variant of the TBX15/WARS2 region first emerged in modern humans from an archaic hominid population, possibly related to the Denisovans. The study authors found that this variant was also present at high frequencies among East Asians and Native American populations, but at low frequencies among Europeans. It is almost absent from African groups. The findings suggest that these gene variants emerged not only in the Arctic, but in a larger geographic region.
"The Denisovan bones that have been found to date come from a cave in Siberia. It is possible that the adaptations we see in this study would have helped archaic humans spread into Siberia and that modern humans borrowed these mutations when they interbred. The archaic variant may have been beneficial to modern humans during their expansion throughout Siberia and into the Americas", Fernando Racimo told IBTimes UK.
The adaptation is associated with changes in expression of WARS2 and TBX15 in multiple fat tissues of the body. It changes body fat distribution and for Inuits, it may be useful in protecting them from the cold climate.