Special Gene Protected Earliest Migrants to Eurasia from Cold Weather

New research has shed light on how prehistoric humans survived the cold after migrating from Africa to various parts of Europe and Asia starting at least 70,000 years ago. In a fascinating study just published in the journal Life Metabolism, a team of Chinese genetic scientists explain how a special gene variant offers extra protection from the cold to humans who possess it, increasing their capacity to live in even the most extreme northern climates.

This variant of the fat-storing FTO gene, which carries the scientific label ‘rs1421085 T>C,’ is unique because of its impact on the metabolism of a person’s brown fat cells. When the human body is exposed to cold conditions this FTO variant accelerates the process of converting potential energy to internal heat in these cells, thereby helping to regulate body temperature and keep a person safe in frigid conditions.

Evolving to Meet the Challenges of New Environments

Over the past several thousand years the different ethnic populations that comprise humanity have become well-established in the zones they occupy on the various continents. This makes it possible to perform an extensive analysis of the DNA of these diverse population groups, to check for genetic variations that might be linked to climate, or to environmental conditions in general.

That is exactly what happened in the newly published study, which was carried out by researchers from the Jiao Tong University School of Medicine in Shanghai and the Shengjing Hospital Medical University in Shenyang. They were looking to find out just how common the FTO variant that offers enhanced body heat production was in different population groups living in the Northern Hemisphere, based on the “mean earth skin temperatures” each group experienced in the month of January.

The Chinese geneticists strongly suspected they would find a correlation between the FTO variant’s frequency and exposure to lower wintertime temperatures – and that is exactly what happened.

The Science

For the purposes of their study, they obtained samples of brown adipose (fat) tissue (BAT) extracted from human fetuses that represented several different population groups. In their analysis they found a strong correlation between climate and the persistence of the rs1421085 T>C variant, with colder climates producing more of the variant.

According to the geneticists, the frequency of the heat-producing variant aligns perfectly with what is known about ancient migration routes. 

“Over the last 100,000 years, modern humans have migrated from low latitudes to high latitudes, transitioning from tropical and temperate zones to colder regions, and shifting from hunter-gatherer societies to agricultural and pastoral lifestyles,” the study authors wrote in an article they published on Higher Education Press.

These environmental changes have imposed evolutionary pressures that have played a pivotal role in shaping phenotypic [genetic] diversity across diverse populations.”

Undergoing a radical change in lifestyle that took them to more challenging environments, prehistoric humans would have had to adapt, and with a helping hand from natural selection their bodies adapted right along with them.

While possessing the ability to produce more body heat would have presumably been helpful to people of any age, it would have been especially vital for the young and vulnerable.

“This variant could confer newborn carriers a substantial survival advantage in cold climates, particularly during the short term after birth, by enhancing BAT thermogenesis [internal heat production],” the genetic researchers explained. “This genetic adaptation may represent just one of the numerous variants early humans employed to acclimate to harsh cold environments. We anticipate that further genetic variants relevant to this intricate evolutionary trajectory will be unraveled in the future.”

The Indian Anomaly

As perfect as the correlation between the incidence of the FTO variant and average January temperatures in most cases, the researchers did stumble across an exception on the Indian subcontinent. In the Indian population as a whole the prevalence of the variant was higher than would be expected, given the warm conditions that predominate in that region.

This can be explained, the researchers say, if what has been called the “Aryan invasion theory” is correct. Supporters of this controversial hypothesis claim that migrants from the north and west arrived on the Indian subcontinent in large numbers in prehistoric times, which ultimately contributed to the decline of ancient Indian civilization. Over time the migrants would have blended into the local population, creating a complex genetic legacy that included a greater occurrence of a genetic variant that boosts the body’s ability to generate its own heat.

In fact, genetic studies have shown that between 20% and 80% of the genetic inheritance of different Indian ethnic populations is Eurasian in origin. So even if the Aryan invasion theory is incorrect in some of its specifics, the modern Indian population is quite genetically diverse, which proves that migration is a factor that must be considered when evaluating the genetic legacy of any group of people.

Navigating the Prehistoric Thin Line between Survival and Demise

Interestingly, the genetic scientists involved in this new study initially were not looking at the FTO gene and its variants within the context of climate adaptation.

When they first began their research years ago, their purpose was to learn more about how the human vulnerability to obesity developed over time. The FTO gene is associated with obesity and greater fat retention, and at one time it was believed that the rs1421085 T>C variant actually increased the risk for obesity even more than other FTO variants.

But after studies in mice showed that this variant could boost the capacity of brown adipose tissue (BAT) cells to burn calories for heat, the Chinese researchers shifted their focus and began to look at how the variant might have protected people from the cold. What they have found confirms the role that the FTO variant plays in amplifying thermogenesis, meaning its presence would have made it easier for prehistoric migrants to cold climates to survive there over the long haul. This variant may also help counteract obesity to some extent, since it boosts fat burning metabolism to a higher level.

“The intricacies of human genetics likely harbor numerous undisclosed secrets regarding cold resistance, alongside countless ancient narratives revolving around survival and demise,” the study authors wrote in their Higher Education Press article, summarizing the greater implications of their discovery. “This enduring repository of our history calls for ceaseless exploration and investigation, offering insights into our complex journey through time and adaptation.”

Top image: Early human trying to keep warm in a cave.                  Source: Erkan/Adobe Stock

By Nathan Falde