Humans have adapted to their various environments over hundreds of thousands of years through a wide variety of both behavioral and behavioral adaptations. genetic. One of the most notable and rapid examples of this are the genetic changes that have led to high altitude tolerance in populations living in areas such as Tibet in southwestern China. However, for most humans, high-altitude locations are extremely difficult to successfully inhabit from a physiological perspective. At 4,000 meters, each breath of air contains only about 60% of the oxygen present at sea level (Yi et al., 2010). For this reason, altitudes above approximately 7,600 meters become lethal for low-altitude humans due to the body's hypoxic response to this severe lack of oxygen. Hypoxia is characterized by a number of adverse symptoms, some of which are minor include fatigue, dizziness, shortness of breath, headache, insomnia, malaise, nausea, vomiting, muscle pain, loss of appetite, ringing in the ears, blisters and dilated veins. . If hypoxia becomes severe enough, cerebral edema (swelling of the brain) or pulmonary edema (build-up of fluid in the lungs), as well as excessive breathing resulting in extra energy being expended even at rest, and eventually a gradually decreasing heart rate until to possible death (Penaloza & Arias-Stella, 2006). Hypoxia is a leading cause of death among mountain climbers, making clear the extreme damage that high altitude conditions can have on the average human body (Huey et al., 2001). Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay However, instead of experiencing some of these life-threatening symptoms in high-altitude areas, Tibetans have remarkably and expertly adapted to their otherwise inhospitable environment on the “roof of the world”. Tibetan populations achieve this with a number of physiological differences compared to humans at low altitudes, such as reduced hemoglobin levels (Yi et al., 2010). Normally, the body increases hemoglobin levels in response to lower oxygen levels to increase the red blood cells' affinity for oxygen; however, this can lead to blood clots, stroke, and even death. Tibetans' bodies are adapted to their environment so that this potentially fatal response does not occur (Gibbons, 2014). Furthermore, they are resistant to the normally progressive reduction in birth weight due to altitude; in fact, in the last two decades a progressive increase in birth weight has been observed in these populations. At birth, babies also experience improved oxygenation to maximize their chances of survival (Yi et al., 2010). Tibetans also breathe more rapidly, inhale more air with each breath, and have larger lung volumes to maximize the amount of oxygen reaching their cells. As a result, their exercise capacity increases. Scientists have also found that Tibetan populations have naturally higher levels of nitric oxide in their blood. This helps blood vessels dilate for better circulation (Beall et al., 2012). Numerous genes have conferred this variety of physiological adaptations, one of the most positive, highly selected, including endothelial PAS domain-containing protein 1, or EPAS1. . EPAS1 is a transcription factor involved in the body's response to hypoxia (Yi et al., 2010). It is associated with a slower than normal increase in red blood cell production due to normally hypoxic conditions, which,as mentioned above, they prevent clots, strokes and death. Furthermore, a gene called EGLN1, which helps to inhibit the production of hemoglobin under conditions of normal oxygen concentration, has also been positively selected among Tibetans. This also helps avoid clots and strokes. PPARA, when inhibited by HIF1a transcription factors, is a gene that prevents the typical reduction in red blood cell production in response to high altitudes, helping to maintain red blood cell levels in concert with EPAS1. Together, these three genes function within the broader hypoxia-inducible factor (HIF) pathway. This pathway generally regulates red blood cell production in response to oxygen metabolism and controls red blood cell production (Simonson et al., 2012; Cheviron & Brumfield, 2011). A second collection of genes important in long-term altitude acclimation that was found alongside these major “candidate” genes are HBB and HBG2, SPTA1, HFE, FANCA, and PLKR. HBB and HBG2 are associated with a delayed transition from fetal to adult hemoglobin, which is thought to help Tibetans prevent a number of potential hematological diseases due to high altitude. SPTA1 is associated with red blood cell shape and HFE with iron accumulation. Finally, FANCA and PLKR are associated with the production and maintenance of red blood cells, respectively (Yi et al., 2010). Because many genes that are close to each other are inherited together, identifying these close genes is valuable in determining how Tibetan populations have adapted genetically to their environment. Furthermore, it has been found that women who possess one or two alleles that confer high blood oxygen content are more likely to produce surviving children; these alleles have also been selected over time (Beall et al., 2004). From extensive genetic analyses, scientists were able to conclude that the EPAS1 allele was acquired by archaic hominins called Denisovans approximately 40,000 years ago (Huerta-Sánchez et al., 2014). Denisovans are more closely related to Neanderthals than to modern humans and once ranged across Asia and into what is now known as Siberia between 35,000 and 25,000 years ago (Gibbons, 2014; Huerta-Sánchez et al., 2014). Denisova Cave in Siberia, where many Denisovan fossils have been found, was at a high altitude, but not as high as the Tibetan Plateau. However, if Denisovans had the high-altitude version of EPAS1, scientists concluded that this could mean that they also crossed the most mountainous parts of China and southern Asia on their way to spread across Australia (Huerta- Sánchez et al., 2014). The Tibetan plateau was then colonized around 30,000 years ago by these ancient hominids. This founding population became the largest Han Chinese/Southeast Asian population; the demographics of high-altitude Tibetans began to diverge from the Han Chinese and Dai approximately 40,000–20,000 years ago (Jeong et al., 2014). Initially, the Tibetan population was large, but over time its size decreased as specific subpopulations became more distinct (Yi et al., 2010). Today, 40% of ethnic Tibetans are nomadic or semi-nomadic, which demonstrates that this population has historically traveled extensively in the area and perhaps indicates some of the ways in which ancient Tibetan populations came to inhabit this area (Pistono, n.d.). This is just one example. Get a custom paper from our expert writers now. Get a Custom Essay Both archaeological and genetic investigations show us that variations in EPAS1 that confer favorable acclimation to altitude occurred less than 3,000 years ago, after.