Sure, everyone wants to go to the mountains for their next vacation – the valleys are pretty and the snow sparkles under the clear, sunny skies, making for extra delightful Instagram and Facebook uploads. But try living in the mountains, not for a week, not for a month, but for your entire lifetime and you’ll quickly find out just how difficult mountain life can be: the air is rare and holds much less oxygen, the higher altitudes mean higher exposure to cancer-causing UV radiation from the sun, and food supply is scarce and unpredictable.
Prolonged exposure to high-altitude environments can lead headaches, a tendency to tire quickly, lower birth rates and higher child mortality.
And yet, more than five million people continue to call the Tibetan Plateau – which has an average elevation of more than 14,800 feet – their home, seemingly unfazed by the potentially harsh reactions their bodies could have to their unforgiving environs.
The air on the Tibetan Plateau has 40 percent less oxygen than at sea level.
In 2010, a team of scientists led by Dr Josef Prchal, a professor of internal medicine at the University of Utah, took a closer look at the DNA of native Tibetans, comparing it to that of the Han Chinese. Through their study, the researchers attempted to isolate the specific genes that enabled Tibetans to adapt to high altitudes, reasoning that any mutations that were common in these people but relatively uncommon in those from the lowlands would be the mutations they were looking for.
THE BIRTH OF THE GENETIC THEORY
While most mountaineers are able to handle higher altitudes with their bodies temporarily increasing the amount of hemoglobin in their blood to carry oxygen more efficiently through their bodies, the way Tibetans handle their mountainous environs is a little different, and for good reason too – blood that contains too much hemoglobin is harder to pump and tends to clot much sooner, leading to an increased occurrence of strokes and heart complications.
Dr. Prchal proposed that the difference lay in the Tibetans’ genetic composition. Working with his team, he found that the gene EGLN1 had changed by a single DNA base pair as far back as 8,000 years ago. This gene influences the human body’s response to falling oxygen levels, and is associated with improved athletic performance in endurance athletes. He also found that this mutation existed in 88 percent of Tibetans.
This mutation is unlike any that researchers have encountered anywhere else in the world. Indigenous tribes in the Peruvian Andes, for example, are able to handle their elevated homes with the help of higher red blood cell counts.
The Tibetans are believed to have inherited their unique mutation from the Denisovans – an ancient sub-species of human beings who went extinct roughly 40,000 years ago.
EVOLVING THE GENETIC CODE
More recently, a team of scientists led by Jian Yang at the University of Queensland in Brisbane, Australia, and Zi-Bing Jin at Wenzhou Medical University in China compared the genomes of 3,008 Tibetans and 7,287 non-Tibetans. This team identified seven additional genes, namely MTHFR, RAP1A, NEK7, ADH7, FGF10, HLA-DQB1, and HCAR2, which are believed to help Tibetans to cope more easily with the pressures of high-altitude living.
While the ADH7 gene helps Tibetans to store energy in their bodies during times when food is harder to come by, MTHFR compensates for nutrient deficiency by boosting the production of the vitamin folate, which is important for fertility and pregnancy. Folate is also known to disintegrate in the presence of elevated UV levels, which helps the Tibetans to handle the increased exposure at higher altitudes.
HLA-DQB1 regulates the production of proteins that are important for immunity, and prevent the Tibetans from becoming more susceptible to disease, despite being exposed to prolonged periods of malnutrition. The other genes in the mix are believed to help the Tibetans to better deal with specific conditions arising from living in higher altitudes.
The team also found that these genetic changes had occurred far more recently than was initially believed – 4,725 years or 189 generations ago, to be specific. This also corresponds with archeological findings that point to Tibetan permanent settlements appearing on the plateau roughly 3,600 to 5,200 years ago.
UNDERSTANDING THE IMPLICATIONS OF GENETIC MUTATION
Developing a better understanding of the way the Tibetans’ genes mutated to help their bodies to adapt to higher altitudes can have broader implications on human health living in plains. Since oxygen plays a very important role in human physiology and disease, these findings could help in the development of innovative treatments to a gamut of diseases such as cancer.
However, there is still some way to go before researchers can even begin to join the dots – for now, scientists are focused on backing this research up with functional studies, to better understand the biological basis for selection.