The ability of native Tibetans to tolerate high altitude is, of course, legendary. Tibetans living on the Tibetan plateau at elevations that exceed 4000 meters are exposed to an atmosphere that has oxygen concentrations that are approximately 40% lower than that which is available at sea level. From a biological perspective it is of interest to know how this has been achieved.
From the evidence accumulated by Jian Wang and his associates from the University of California at Berkeley, Tibetans have acquired a number of inherited adaptations to this extreme environment, including – higher birth weight, higher hemoglobin – the protein found in red blood cells that binds oxygen - levels, higher oxygen saturation in the blood of infants and adults following exercise when compared with a control group of Han Chinese who moved to Tibet and are genetically distinct. Tibetans have occupied the Tibetan Plateau for over 25,000 years, possibly enough time to accumulate genetic adaptations through natural selection.
In an attempt to delineate the genetic characteristics of these adaptations, the investigators analyzed the DNA from both Tibetans and the control group. There results demonstrated, in fact, a single-nucleotide polymorphism (SNP) – a single point variation in the DNA studied – from a gene that encodes for the EPAS1 protein. This protein has been shown to be involved in the body’s response to hypoxia – low oxygen environment. This change occurred at a much higher frequency in native Tibetans than in the control group of Han Chinese.
These results represent a very important finding in regards to the fact that this beneficial genetic modification occurred over a very brief interval of time as compared to previously studied human genetic adaptations.