Athletes are known for trying to increase their capacity to process oxygen. Increased blood oxygen levels have many benefits for those wishing to increase their aerobic capacity and endurance during exercise, and small increases in blood oxygen capacity can be achieved by training at high altitudes where oxygen levels are lower. While athletes are focussing on short time frames of one individual, several scientists have begun asking what the effects of living at high altitudes are for populations on an evolutionary time scale. Peoples living at greater than 8,000 feet above sea level have clearly adapted to their environment, as non-natives that attempt to live at such high altitudes often suffer from acute hypoxia, which is absent in natives.
One well-studied and understood example of this type of adaptation occurs in native South Americans living on the Andean Plateau. Compared to lowlanders, they breathe at the same rate, have a similar red blood cell count and do not have any novel hemoglobin variants. However, each red blood cell in the body holds a greater amount of total hemoglobin. This allows for the transport of more gasses throughout the body without increasing blood viscosity. This is in contrast to Tibetans, who have been found to have unchanged hemoglobin levels, but simply take more breaths during a given time, which increases the rate of gas exchange in the lungs. They have also been found to have abnormally high levels of nitrous oxide int heir blood, which is a gas synthesized in the body that triggers vasodialation. This increases blood flow to peripheral tissues and increase the rate of gas exchange. A third population located in the highlands of Ethiopia has been investigated as well, but no change in any of the variables already mentioned were found. This suggests that there are more subtle or complex factors regulating gas exchange, and may open up an exciting new line of investigation.
