Human Variation

Humans who move to higher altitudes will experience the following environmental stresses: hypoxia which is caused by a reduction in the concentration of oxygen, more intense climatic conditions such as low humidity, greater exposure to the sun, cold and wind and rough terrain and reduced nutrition.  In addition, infant mortality is greater at higher altitudes as a result of a condition called preeclampsia.  Preeclampsia causes a severe elevation in blood pressure in pregnant women after the twentieth gestation week. All of these conditions disturb homeostasis in humans and impact their ability to thrive at the higher altitudes.

Humans have developed a number of mechanisms to adapt to living at higher altitudes.  Individuals who have recently moved to a higher altitude will acclimatize in a few days by experiencing an increased respiratory and heart rate. In addition a facultative response will occur when the body produces more red blood cells to increase the oxygen supply to internal organs and tissues.  Over time, natural selection will act on individuals born at higher altitudes since they will show developmental characteristics such as increased chest size to accommodate a greater lung volume and larger heart.  Cultural products have also been developed such as the medicine Diamox which is designed to help ease many of the symptoms experienced during the acclimatization process.

The benefits of studying human variation across environmental clines, is that it allows scientists to understand the human’s evolutionary response to changing environmental conditions. The information gained from these studies can then be used to predict how humans will respond to future climate changes such as global warming.

Race is not a useful measure when looking at how humans adapt to changes in altitude.  While certain groups of individuals such as the Tibetans and Quechua have shown a remarkable ability to survive at altitudes as high as 12,000 feet, there is no evidence that suggests that these individuals have a greater capacity to survive in these conditions than other groups of individuals.  Over thousands of years, natural selection has acted on these groups of individuals which has allowed their bodies to adapt to the extreme living conditions.