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High-altitude adaptation in humans
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High-altitude adaptation in humans
High-altitude adaptation in humans is an instance of evolutionary modification in certain human populations, including those of Tibet in Asia, the Andes of the Americas, and the Amhara of Ethiopia, who have evolved the ability to survive at altitudes above 2,500 meters (8,200 ft). This adaptation means irreversible, long-term physiological responses to high-altitude environments associated with heritable behavioral and genetic changes. While the rest of the human population would suffer serious health consequences at high altitudes, the indigenous inhabitants of these regions thrive in the highest parts of the world. These humans have undergone extensive physiological and genetic changes, particularly in the regulatory systems of oxygen respiration and blood circulation when compared to the general lowland population.
Around 81.6 million humans (approximately 1.1% of the world's human population) live permanently at altitudes above 2,500 meters (8,200 ft), which would seem to put these populations at risk for chronic mountain sickness (CMS). However, the high-altitude populations in South America, East Africa, and South Asia have lived there for millennia without apparent complications. This special adaptation is now recognized as an example of natural selection in action. The adaptation of the Tibetans is the fastest known example of human evolution, as it is estimated to have occurred between 1,000 BCE to 7,000 BCE.
Humans are generally adapted to lowland environments where oxygen is abundant. At altitudes above 2,500 meters (8,200 ft), such humans experience altitude sickness, which is a type of hypoxia, a clinical syndrome of severe lack of oxygen. Some humans develop the illness beginning at above 1,500 meters (5,000 ft). Symptoms include fatigue, dizziness, breathlessness, headaches, insomnia, malaise, nausea, vomiting, body pain, loss of appetite, ear-ringing, blistering and purpling of the hands and feet, and dilated blood vessels.
The sickness is compounded by related symptoms such as cerebral oedema (swelling of brain) and pulmonary oedema (fluid accumulation in lungs) . Over a span of multiple days, individuals experiencing the effects of high-altitude hypoxia demonstrate raised respiratory activity and elevated metabolic conditions which persist during periods of rest. Subsequently, afflicted people will experience slowly declining heart rate. Hypoxia is a primary contributor to fatalities within mountaineering groups, making it a significant risk factor within high-altitude related challenges. In women, pregnancy can be severely affected, such as development of preeclampsia, which causes premature labor, low birth weight of babies, and often complicates with profuse bleeding, seizures, or death of the mother.
An estimated 81.6 million humans live at an elevation higher than 2,500 meters (8,200 ft) above sea level, of which 21.7 million reside in Ethiopia, 12.5 million in China, 11.7 million in Colombia, 7.8 million in Peru, and 6.2 million in Bolivia. Certain natives of Tibet, Ethiopia, and the Andes have been living at these high altitudes for generations and are resistant to hypoxia as a consequence of genetic adaptation. It is estimated that at 4,000 meters (13,000 ft) altitude, every lungful of air has approximately 60% of the oxygen molecules found in a lungful of air at sea level. Highlanders are thus constantly exposed to a low oxygen environment, yet they live without any debilitating problems.
One of the best-documented effects of high altitude on non-adapted women is a progressive reduction in birth weight. By contrast, the women of long-resident, high-altitude populations are known to give birth to heavier-weight infants than women of the lowland. This is particularly true among Tibetan babies, whose average birth weight is 294–650g (~470) g heavier than the surrounding Chinese population, and their blood-oxygen level is considerably higher.
Scientific investigation of high-altitude adaptation was initiated by A. Roberto Frisancho of the University of Michigan in the late 1960s among the Quechua people of Peru. Paul T. Baker of Penn State University's Department of Anthropology also conducted a considerable amount of research into human adaptation to high altitudes, and mentored students who continued this research. One of these students, anthropologist Cynthia Beall of Case Western Reserve University, began conducting decades-long research on high altitude adaptation among the Tibetans in the early 1980s.
Among the different native highlander populations, the underlying physiological responses to adaptation differ. For example, among four quantitative features, such as resting ventilation, hypoxic ventilatory response, oxygen saturation, and hemoglobin concentration, the levels of variations are significantly different between the Tibetans and the Aymaras. Methylation also influences oxygenation.
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High-altitude adaptation in humans
High-altitude adaptation in humans is an instance of evolutionary modification in certain human populations, including those of Tibet in Asia, the Andes of the Americas, and the Amhara of Ethiopia, who have evolved the ability to survive at altitudes above 2,500 meters (8,200 ft). This adaptation means irreversible, long-term physiological responses to high-altitude environments associated with heritable behavioral and genetic changes. While the rest of the human population would suffer serious health consequences at high altitudes, the indigenous inhabitants of these regions thrive in the highest parts of the world. These humans have undergone extensive physiological and genetic changes, particularly in the regulatory systems of oxygen respiration and blood circulation when compared to the general lowland population.
Around 81.6 million humans (approximately 1.1% of the world's human population) live permanently at altitudes above 2,500 meters (8,200 ft), which would seem to put these populations at risk for chronic mountain sickness (CMS). However, the high-altitude populations in South America, East Africa, and South Asia have lived there for millennia without apparent complications. This special adaptation is now recognized as an example of natural selection in action. The adaptation of the Tibetans is the fastest known example of human evolution, as it is estimated to have occurred between 1,000 BCE to 7,000 BCE.
Humans are generally adapted to lowland environments where oxygen is abundant. At altitudes above 2,500 meters (8,200 ft), such humans experience altitude sickness, which is a type of hypoxia, a clinical syndrome of severe lack of oxygen. Some humans develop the illness beginning at above 1,500 meters (5,000 ft). Symptoms include fatigue, dizziness, breathlessness, headaches, insomnia, malaise, nausea, vomiting, body pain, loss of appetite, ear-ringing, blistering and purpling of the hands and feet, and dilated blood vessels.
The sickness is compounded by related symptoms such as cerebral oedema (swelling of brain) and pulmonary oedema (fluid accumulation in lungs) . Over a span of multiple days, individuals experiencing the effects of high-altitude hypoxia demonstrate raised respiratory activity and elevated metabolic conditions which persist during periods of rest. Subsequently, afflicted people will experience slowly declining heart rate. Hypoxia is a primary contributor to fatalities within mountaineering groups, making it a significant risk factor within high-altitude related challenges. In women, pregnancy can be severely affected, such as development of preeclampsia, which causes premature labor, low birth weight of babies, and often complicates with profuse bleeding, seizures, or death of the mother.
An estimated 81.6 million humans live at an elevation higher than 2,500 meters (8,200 ft) above sea level, of which 21.7 million reside in Ethiopia, 12.5 million in China, 11.7 million in Colombia, 7.8 million in Peru, and 6.2 million in Bolivia. Certain natives of Tibet, Ethiopia, and the Andes have been living at these high altitudes for generations and are resistant to hypoxia as a consequence of genetic adaptation. It is estimated that at 4,000 meters (13,000 ft) altitude, every lungful of air has approximately 60% of the oxygen molecules found in a lungful of air at sea level. Highlanders are thus constantly exposed to a low oxygen environment, yet they live without any debilitating problems.
One of the best-documented effects of high altitude on non-adapted women is a progressive reduction in birth weight. By contrast, the women of long-resident, high-altitude populations are known to give birth to heavier-weight infants than women of the lowland. This is particularly true among Tibetan babies, whose average birth weight is 294–650g (~470) g heavier than the surrounding Chinese population, and their blood-oxygen level is considerably higher.
Scientific investigation of high-altitude adaptation was initiated by A. Roberto Frisancho of the University of Michigan in the late 1960s among the Quechua people of Peru. Paul T. Baker of Penn State University's Department of Anthropology also conducted a considerable amount of research into human adaptation to high altitudes, and mentored students who continued this research. One of these students, anthropologist Cynthia Beall of Case Western Reserve University, began conducting decades-long research on high altitude adaptation among the Tibetans in the early 1980s.
Among the different native highlander populations, the underlying physiological responses to adaptation differ. For example, among four quantitative features, such as resting ventilation, hypoxic ventilatory response, oxygen saturation, and hemoglobin concentration, the levels of variations are significantly different between the Tibetans and the Aymaras. Methylation also influences oxygenation.