Human Variation & Race Example

High-Altitude Human Adaptation

High altitude is one of the most straining environmental stresses humans can encounter. This is because the mechanisms that maintain homeostasis (the process by which living organisms maintain a stable internal environment despite changes in external conditions) evolved at lower altitudes. At high altitudes, people face hypoxia, more intense solar radiation, cold temperatures, low humidity, wind (which amplifies the effects of cold stress), a reduced nutritional base, and rough terrain. Hypoxia (insufficient levels of oxygen in body tissues) causes the most problems. Initial symptoms of “altitude sickness” include fatigue, lack of appetite, vomiting, headache, distorted vision, and difficulty with memorizing and thinking clearly. In severe cases, it can lead to pulmonary edema (pneumonia-like symptoms due to hemorrhaging in the lungs) and cerebral edema (abnormal accumulation of fluid around the brain), which usually result in death within a few days if there is not a return to normal air pressure levels.

When people travel to high elevations, they undergo a series of short-term, facultative, developmental, and cultural adaptations. In the short term, people will experience an increase in breathing and heart rates, sometimes doubling – even at rest. This response helps compensate for the reduced oxygen levels in the atmosphere by bringing more oxygen and circulating it more rapidly. One facultative adaptation that occurs is the production of more red blood cells and capillaries. This allows the bloodstream to carry more oxygen throughout the body. One famous example of a developmental adaptation is the Tibetan’s (whose ancestors have lived at elevations above 12,000 feet for 7,000 to possibly 25,000 years) point mutation in the EPAS1 gene. This mutation actually inhibits the facultative adaptation discussed earlier, allowing Tibetans to maintain red cell counts similar to those of sea-level populations. This reduces the risk of stroke, blood clots, heart attack, and impaired fetal growth that occurs with excessively high red blood cell counts. One famous example of a cultural adaptation can be found in another high-altitude indigenous culture: the Andean’s (whose ancestors have lived at elevations above 8,000 feet for 9,000 to possibly 12,000 years) use of coca leaves. Coca leaves contain mild stimulants that help improve oxygen efficiency and reduce fatigue, nausea, and hunger. This cultural practice has been passed down for generations, plays an essential role in rituals, and helps the Andeans cope with the thin air of the Andes.

Short-term Heart Rate Adaptation:

Facultative Red Blood Cell Adapatation:

Developmental EPAS1 Gene Adaptation:

Cultural Coca Leave Adaptation:

Studying human variations in high-altitude environments offers many benefits. Most notably, it enhances our understanding of adaptation. When scientists identify patterns in how traits are expressed across different environments, it leads to deeper insights into how humans adapt to specific environmental pressures. Beyond providing new information, however, researching specific human adaptations can produce medical insights. For example, understanding genetic adaptations to high altitude (like the EPAS1 gene in Tibetans) could inform treatments for hypoxia. Researching cultural practices could also reveal strategies for addressing specific environmental conditions. For example, studying high-altitude cultural practices (such as the Andean’s use of coca leaves) could inform travelers from low-altitude climates on ways to mitigate the effects of altitude sickness. Ultimately, understanding human adaptation can enhance our understanding of adaptation, lead to medical advancements, and provide insights into techniques for addressing specific environmental challenges.

Many people look to race to explain human adaptations, but dividing the human species into racial categories is not a biologically valid way to understand variation. The idea of “pure races” is both false and harmful, with no scientific evidence to support their existence. Traits commonly used to define race—such as skin color—are polygenic (influenced by multiple genes) and vary along a continuous spectrum, making it nearly impossible to draw clear boundaries between populations. In contrast, studying environmental influences offers a more accurate approach. It directly links human variation to evolutionary forces (e.g., natural selection, genetic drift, gene flow, and mutation). This method allows researchers to examine variation at the genetic level, identifying specific genes and mutations responsible for adaptive traits—something broad racial categories cannot do.