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 Ethiopia in Africa, who have acquired 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 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 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 sf), putting these populations at risk for chronic mountain sickness (CMS). However, the high-altitude populations in South America, East Africa, and South Asia have done so for millennia without apparent complications. This special adaptation is now recognised 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 any time around 1,000 BCE. to 7,000 BCE. Humans are naturally adapted to lowland environments where oxygen is abundant. When humans from the general lowlands go to altitudes above they experience altitude sickness, which is a type of hypoxia, a clinical syndrome of severe lack of oxygen. Some humans get the illness even 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) .