page_title: High-altitude adaptation in humans
section_title: Andeans
hierarchical_section_title: High-altitude adaptation in humans / Physiological basis / Andeans
caption_attribution_description: English: Photos of a traditional Aymara ceremony in Copacabana, on the border of Lake Titicaca in Bolivia.
context_page_description: 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 Ethiopia in Africa, who have acquired the ability to survive at extremely high altitudes. This adaptation means irreversible, long-term physiological responses to high-altitude environments, associated with heritable behavioural and genetic changes. While the rest of the human population would suffer serious health consequences, the indigenous inhabitants of these regions thrive well in the highest parts of the world. These people 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 140 million people, just under 2% of the world's human population, live permanently at altitudes above 2,500 metres in South America, East Africa, and South Asia. These populations have done so for millennia without apparent complications. This special adaptation is now recognised as an example of natural selection in action.
context_section_description: In contrast to the Tibetans, the Andean highlanders, who have been living at high altitudes for no more than 11,000 years, show different pattern of haemoglobin adaptation. Their haemoglobin concentration is higher compared to those of lowlander population, which also happens to lowlanders moving to high altitude. When they spend some weeks in the lowland their haemoglobin drops to average of other people. This shows only temporary and reversible acclimatisation. However, in contrast to lowland people, they do have increased oxygen level in their haemoglobin, that is, more oxygen per blood volume than other people. This confers an ability to carry more oxygen in each red blood cell, making a more effective transport of oxygen in their body, while their breathing is essentially at the same rate. This enables them to overcome hypoxia and normally reproduce without risk of death for the mother or baby. The Andean highlanders are known from the 16th-century missionaries that their reproduction had always been normal, without any effect in the giving birth or the risk for early pregnancy loss, which are common to hypoxic stress. They have developmentally acquired enlarged residual lung volume and its associated increase in alveolar area, which are supplemented with increased tissue thickness and moderate increase in red blood cells. Though the physical growth in body size is delayed, growth in lung volumes is accelerated. An incomplete adaptation such as elevated haemoglobin levels still leaves them at risk for mountain sickness with old age. 
  Among the Quechua people of the Altiplano, there is a significant variation in NOS3 (the gene encoding endothelial nitric oxide synthase, eNOS), which is associated with higher levels of nitric oxide in high altitude. Nuñoa children of Quechua ancestry exhibit higher blood-oxygen content (91.3) and lower heart rate (84.8) than their counterpart school children of different ethnicity, who have an average of 89.9 blood-oxygen and 88–91 heart rate. High-altitude born and bred females of Quechua origins have comparatively enlarged lung volume for increased respiration. 
  Blood profile comparisons show that among the Andeans, Aymaran highlanders are better adapted to highlands than the Quechuas. Among the Bolivian Aymara people, the resting ventilation and hypoxic ventilatory response were quite low (roughly 1.5 times lower), in contrast to those of the Tibetans. The intrapopulation genetic variation was relatively less among the Aymara people. Moreover, when compared to Tibetans, the blood haemoglobin level at high altitudes among Aymarans is notably higher, with an average of 19.2 g/dl for males and 17.8 g/dl for females. Among the different native highlander populations, the underlying physiological responses to adaptation are quite different. For example, among four quantitative features, such as are resting ventilation, hypoxic ventilatory response, oxygen saturation, and haemoglobin concentration, the levels of variations are significantly different between the Tibetans and the Aymaras.
caption: Aymara ceremony
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