One of the most commonly cited examples of developmental adaptation to environmental stress is hypoxic stress (experienced from birth throughout the period of growth and development).

After reading HIGH ALTITUDE AND ACCESS TO OXYGEN, describe in your own words what permanent changes are seen in these individuals that relate directly to the hypoxic environment they grew up in. Are there any other environments where these adaptations might be helpful?

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HIGH ALTITUDE AND ACCESS TO OXYGEN:

At high altitudes, generally defined as greater than 3 km (10,000 ft) above sea level, a fall in barometric pressure reduces oxygen molecules.

The primary environmental stress in such places is hypoxia, the condition in which body tissues receive insufficient amounts of Oxygen. Secondary stresses include high UV radiation, cold, wind, nutritional deprivation, and the rigors of living in highly variable, generally rugged terrain.

The severity of hypoxia increases as a person moves higher, and the associated risk increases because all body tissues and physiological processes require an uninterrupted oxygen supply.

Hypoxia results in mountain sickness, with headache, nausea, loss of appetite, fatigue, and breathlessness occurring at about 2.4 km (8,000 ft) during rest and about 1.9 km (6,500 ft) during physical activity. For some individuals living at sea level or in prehypoxic conditions who travel to high altitudes or otherwise experience hypoxia, mountain sickness becomes a life-threatening condition.

For most people, the symptoms disappear within the first few days of exposure the body begins to more efficiently use reduced amounts of oxygen in the air and homeostasis is restored. Extra red blood cells and oxygen-saturated hemoglobin are produced. The hemoglobin transports oxygen to body tissues, while an expansion in the diameter of arteries and of veins allows increased blood flow and increased access to oxygen.

Additional physiological changes represent a long-term response to hypoxia. A person who moved to the high-altitude settings of the Himalayas, for example, would function better there over time. A young child who moved there would, through the process of growth, develop greater lung volume and the ability to use oxygen more efficiently. Human populations who have lived at high altitudes for many generations-such as those in the Peruvian Andes-have larger chest cavities than do populations at low altitudes, reflecting the high-altitude populations' inherited increases in lung volume. However, these populations are generally shorter than their low-altitude counterparts. Widespread growth retardation results from the increased energy required to live in cold environments with little oxygen and poor nutrition. But some biological attributes associated with living at high altitudes may offer selective advantages. For example, the American physical anthropologist Cynthia Beall and colleagues have found that Tibetan women with alleles for high oxygen saturation in their hemoglobin, a factor that enhances the body's access to oxygen, have more surviving children. Thus, hypoxia at high altitudes can be an agent of natural selection.