A research report published by scientists from the University of California, Berkeley revealed the secret of the adaptability of Tibetans to high altitudes.

According to the report, Tibetans received a gene from their ancestors, who mated with a human species that was pushed to extinction.

The gene is an unusual variant of one that is part of the regulation of the body's production of hemoglobin, which is the molecule tasked with carrying oxygen in a person's blood. The gene became widespread among Tibetans once they moved to live in the high-altitude plateaus of the country thousands upon thousands of years ago.

The variant gene gave Tibetans the ability to survive in high altitudes, despite the low levels of oxygen that is characteristic of heights of 15,000 feet and more. Most people, when exposed to these harsh conditions, develop thickness in their blood which leads to problems in the body's cardiovascular system.

UC Berkeley integrative biology professor Rasmus Nielsen, the principal author of the research, states that the gene variant came from the Denisovans, which are a mysterious human species that became extinct 40,000 to 50,000 years ago. Their disappearance was about the same time as the Neanderthals, which Homo Sapiens, or the modern man, likewise pushed into extinction as the more dominant and advanced species.

The researchers state that their findings show for the first time that a gene from another human species undisputedly helped modern humans to adapt to the environment.

The gene, which is named EPAS1, triggers the production of additional hemoglobin when the oxygen levels in the blood decreases. It is capable of increasing the endurance of people in low elevations, helping athletes boost hemoglobin and the oxygen-carrying capabilities of their blood, earning it the nickname as the "superathlete" gene. However, at high elevations, EPAS1 increases hemoglobin and red blood cells too much, which leads to heart attacks and hypertension. In addition, thicker blood leads to babies with low weights upon birth and higher infant mortality.

However, the variant found in Tibetans only slightly raises hemoglobin and red blood cells at high altitudes, which allows them to bypass the dangerous side effects of living in high places.

"We found that part of the EPAS1 gene in Tibetans is almost identical to the gene in Denisovans and very different from all other humans," said Nielsen. "We can do a statistical analysis to show that this must have come from Denisovans. There is no other way of explaining the data." 

The research report was published in the Nature journal, bringing light to how people have thrived in the harsh plateaus of Tibet for thousands of years.