What is common between a Nepali drinking milk (and experiencing the usual upset stomach) and high altitude adaptation? The DNA.
About 7,000 years ago, Northern Europeans learnt how to digest milk, a clear human evolutionary change. But many people in South Asia including Nepal have not made this genetic switch and predominantly suffer from lactose intolerance (milk indigestion), which accounts for our ‘pet gadyang gudung’ after consuming a glass or two of milk. The newest example of documented evolutionary change may well be in the field of high altitude adaptation by the Tibetans and Sherpa people.
Independent reports some years ago from Beijing Genomics Institute (the world’s largest genetic research centre designed to sequence the precise order of billions of chemicals within the molecule of DNA), Case Western Reserve University in Ohio, and University of Utah have detected mutations in a gene which helps the Tibetans to adapt to high altitude. The gene, called Hypoxia Inducible Factor (HIF 2 alpha, to be precise), seems to be able to assist in properly adapting to high altitude in the same fashion that the Europeans avoid milk indigestion by a genetic switch.
There are high altitude dwellers in other parts of the world such as South America, but the natives there do not seem to properly adapt at high altitude; in fact they mal adapt, probably due to lack of changes in HIF.
Chronic mountain sickness (CMS), also known as Monge’s Disease after a well-known Peruvian high altitude scientist, is a common disease in South America among residents of altitudes above 2,500m. It is characterised by excessive red blood cells (polycythemia) and leads to edema, heart failure, and lethargy. CMS is completely different from acute mountain sickness (AMS), which is characterised by headache and nausea in short-term travellers to the Himalayas.
The Altiplano in South America that stretches across Bolivia, Peru, Chile, and Argentina, is the largest and highest plateau after the one in Tibet. In cities and towns that fall on the Andean Plateau, CMS is commonly seen. CMS is also seen in certain high altitude areas in Colorado, USA, and more recently amongst the thousands of Han Chinese who have recently arrived in high altitude towns and cities in the Tibetan plateau such as Lhasa.
None of these other high altitude residents possess the mutation in the particular HIF gene, thus strongly suggesting a genetic contribution to the adaptation in the Tibetans and Sherpas. Migration to a low altitude results in the resolution of CMS.
Altitude adaptation is also important for animals living at high altitude. Brisket disease is seen in regular cattle who are taken to high altitude. There is obvious water collection (edema) in the forelegs and neck of these animals due to heart failure caused by low oxygen. The symptoms improve and the animal is eventually cured by taking it back to low altitude. ColonelDr Anand from Chandigarh, Punjab described a very similar disease to Brisket in young Indian soldiers stationed at high altitude near the border with Pakistan. The soldiers also were cured of their illness on descent.
But the animal which has learnt to survive (indeed thrive) at high altitudes is the yak. Even at 5,000m the beast has no problems with lack of oxygen. Studies in yaks have revealed useful changes in the HIF gene, suggesting that certain varieties of this gene may play an important role in adaptation even in animals. Indeed, there seems to be a positive genetic contribution to both long-term human and animal habitation at high altitude in the Himalayas.