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Organisms can live at
high altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...
, either on land, in water, or while flying. Decreased oxygen availability and decreased temperature make life at such altitudes challenging, though many species have been successfully
adapted In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
via considerable physiological changes. As opposed to short-term
acclimatisation Acclimatization or acclimatisation ( also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), a ...
(immediate physiological response to changing environment), high-altitude adaptation means irreversible, evolved physiological responses to high-altitude environments, associated with heritable
behavioural Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as wel ...
and genetic changes. Among animals, only few mammals (such as yaks,
ibex An ibex (plural ibex, ibexes or ibices) is any of several species of wild goat (genus ''Capra''), distinguished by the male's large recurved horns, which are transversely ridged in front. Ibex are found in Eurasia, North Africa and East Africa ...
es,
Tibetan gazelle The goa (''Procapra picticaudata''), also known as the Tibetan gazelle, is a species of antelope that inhabits the Tibetan plateau. Description The goa is a relatively small antelope, with slender and graceful bodies. Both males and females st ...
s, vicunas,
llama The llama (; ) (''Lama glama'') is a domesticated South American camelid, widely used as a meat and pack animal by Andean cultures since the Pre-Columbian era. Llamas are social animals and live with others as a herd. Their wool is soft ...
s,
mountain goat The mountain goat (''Oreamnos americanus''), also known as the Rocky Mountain goat, is a hoofed mammal endemic to mountainous areas of western North America. A subalpine to alpine species, it is a sure-footed climber commonly seen on cliffs an ...
s, etc.) and certain
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s are known to have completely adapted to high-altitude environments. Human populations such as some
Tibetans The Tibetan people (; ) are an East Asian ethnic group native to Tibet. Their current population is estimated to be around 6.7 million. In addition to the majority living in Tibet Autonomous Region of China, significant numbers of Tibetans liv ...
,
South Americans South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
and
Ethiopians Ethiopians are the native inhabitants of Ethiopia, as well as the global diaspora of Ethiopia. Ethiopians constitute several component ethnic groups, many of which are closely related to ethnic groups in neighboring Eritrea and other parts o ...
live in the otherwise uninhabitable high mountains of the
Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 10 ...
,
Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
and
Ethiopian Highlands The Ethiopian Highlands is a rugged mass of mountains in Ethiopia in Northeast Africa. It forms the largest continuous area of its elevation in the continent, with little of its surface falling below , while the summits reach heights of up to . ...
respectively. The adaptation of humans to high altitude is an example of
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
in action. High-altitude adaptations provide examples of
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
, with adaptations occurring simultaneously on three continents. Tibetan humans and Tibetan domestic dogs share a genetic mutation in ''
EPAS1 Endothelial PAS domain-containing protein 1 (EPAS1, also known as hypoxia-inducible factor-2alpha (HIF-2α)) is a protein that is encoded by the ''EPAS1'' gene in mammals. It is a type of hypoxia-inducible factor, a group of transcription factor ...
'', but it has not been seen in Andean humans.


Invertebrates

Tardigrades Tardigrades (), known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbär ...
live over the entire world, including the high
Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 10 ...
. Tardigrades are also able to survive temperatures of close to absolute zero (), temperatures as high as , radiation that would kill other animals, and almost a decade without water. Since 2007, tardigrades have also returned alive from studies in which they have been exposed to the vacuum of outer space in low Earth orbit. Other invertebrates with high-altitude habitats are ''
Euophrys omnisuperstes ''Euophrys omnisuperstes'' (the species name means ''standing above everything''), the Himalayan jumping spider, is a small and toxic jumping spider that lives at elevations of up to in the Himalayas, including Mount Everest, making it a candida ...
'', a spider that lives in the Himalaya range at altitudes of up to ; it feeds on stray insects that are blown up the mountain by the wind. The
springtail Springtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects (the other two are the Protura and Diplura). Although the three orders are sometimes grouped together in a class called Ento ...
''
Hypogastrura nivicola ''Hypogastrura nivicola'' is a species of dark blue springtail. Its (US) English name is snow flea, but there are also insects called by that name. They are often seen jumping about on the surface of snow on a warm winter day in North America. Re ...
'' (one of several insects called snow fleas) also lives in the Himalayas. It is active in the dead of winter, its blood containing a compound similar to
antifreeze An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, all ...
. Some allow themselves to become dehydrated instead, preventing the formation of ice crystals within their body. Insects can fly and kite at very high altitude.
Flies Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced m ...
are common in the Himalaya up to .
Bumble bee A bumblebee (or bumble bee, bumble-bee, or humble-bee) is any of over 250 species in the genus ''Bombus'', part of Apidae, one of the bee families. This genus is the only extant group in the tribe Bombini, though a few extinct related genera ...
s were discovered on
Mount Everest Mount Everest (; Tibetic languages, Tibetan: ''Chomolungma'' ; ) is List of highest mountains on Earth, Earth's highest mountain above sea level, located in the Mahalangur Himal sub-range of the Himalayas. The China–Nepal border ru ...
at more than above sea level. In subsequent tests, bumblebees were still able to fly in a flight chamber which recreated the thinner air of . Ballooning is a term used for the mechanical kiting that many
spider Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...
s, especially small species such as '' Erigone atra'', as well as certain
mite Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear e ...
s and some caterpillars use to disperse through the air. Some spiders have been detected in atmospheric data balloons collecting air samples at slightly less than 5 km (16000 ft) above sea level. It is the most common way for spiders to pioneer isolated islands and mountaintops.


Fish

Fish at high altitudes have a lower metabolic rate, as has been shown in highland
westslope cutthroat trout The westslope cutthroat trout (''Oncorhynchus clarkii lewisi''), also known as the black-spotted trout, common cutthroat trout and red-throated trout is a subspecies of the cutthroat trout (''Oncorhynchus clarkii'') and is a freshwater fish in t ...
when compared to introduced lowland rainbow trout in the
Oldman River The Oldman River is a river in southern Alberta, Canada. It flows roughly west to east from the Rocky Mountains, through the communities of Fort Macleod, Lethbridge, and on to Grassy Lake, where it joins the Bow River to form the South Saskatchew ...
basin. There is also a general trend of smaller body sizes and lower
species richness Species richness is the number of different species represented in an ecological community, landscape or region. Species richness is simply a count of species, and it does not take into account the abundances of the species or their relative ab ...
at high altitudes observed in aquatic invertebrates, likely due to lower oxygen partial pressures. These factors may decrease
productivity Productivity is the efficiency of production of goods or services expressed by some measure. Measurements of productivity are often expressed as a ratio of an aggregate output to a single input or an aggregate input used in a production proces ...
in high altitude habitats, meaning there will be less energy available for consumption, growth, and activity, which provides an advantage to fish with lower metabolic demands. The naked carp from Lake Qinghai, like other members of the carp family, can use gill remodelling to increase oxygen uptake in hypoxic environments. The response of naked carp to cold and low-oxygen conditions seem to be at least partly mediated by hypoxia-inducible factor 1 (HIF-1). It is unclear whether this is a common characteristic in other high altitude dwelling fish or if gill remodelling and HIF-1 use for cold adaptation are limited to carp.


Mammals

Mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur o ...
are also known to reside at high altitude and exhibit a striking number of adaptations in terms of
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
,
physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
and behaviour. The
Tibetan Plateau The Tibetan Plateau (, also known as the Qinghai–Tibet Plateau or the Qing–Zang Plateau () or as the Himalayan Plateau in India, is a vast elevated plateau located at the intersection of Central, South and East Asia covering most of the ...
has very few mammalian species, ranging from
wolf The wolf (''Canis lupus''; : wolves), also known as the gray wolf or grey wolf, is a large canine native to Eurasia and North America. More than thirty subspecies of ''Canis lupus'' have been recognized, and gray wolves, as popularly un ...
,
kiang The kiang (''Equus kiang'') is the largest of the '' Asinus'' subgenus. It is native to the Tibetan Plateau, where it inhabits montane and alpine grasslands. Its current range is restricted to the plains of the Tibetan plateau; Ladakh; and nort ...
(Tibetan wild ass), goas,
chiru The Tibetan antelope or chiru (''Pantholops hodgsonii'') (, pronounced ; ) is a medium-sized bovid native to the northeastern Tibetan plateau. Most of the population live within the Chinese border, while some scatter across India and Bhutan in ...
(Tibetan antelope), wild yak,
snow leopard The snow leopard (''Panthera uncia''), also known as the ounce, is a felid in the genus '' Panthera'' native to the mountain ranges of Central and South Asia. It is listed as Vulnerable on the IUCN Red List because the global population is es ...
, Tibetan sand fox,
ibex An ibex (plural ibex, ibexes or ibices) is any of several species of wild goat (genus ''Capra''), distinguished by the male's large recurved horns, which are transversely ridged in front. Ibex are found in Eurasia, North Africa and East Africa ...
,
gazelle A gazelle is one of many antelope species in the genus ''Gazella'' . This article also deals with the seven species included in two further genera, '' Eudorcas'' and '' Nanger'', which were formerly considered subgenera of ''Gazella''. A third ...
, Himalayan brown bear and
water buffalo The water buffalo (''Bubalus bubalis''), also called the domestic water buffalo or Asian water buffalo, is a large bovid originating in the Indian subcontinent and Southeast Asia. Today, it is also found in Europe, Australia, North America, So ...
. These mammals can be broadly categorised based on their adaptability in high altitude into two broad groups, namely ''eurybarc'' and ''stenobarc''. Those that can survive a wide range of high-altitude regions are ''eurybarc'' and include yak, ibex,
Tibetan gazelle The goa (''Procapra picticaudata''), also known as the Tibetan gazelle, is a species of antelope that inhabits the Tibetan plateau. Description The goa is a relatively small antelope, with slender and graceful bodies. Both males and females st ...
of the Himalayas and
vicuña The vicuña (''Lama vicugna'') or vicuna (both , very rarely spelled ''vicugna'', its former genus name) is one of the two wild South American camelids, which live in the high alpine areas of the Andes, the other being the guanaco, which live ...
s
llama The llama (; ) (''Lama glama'') is a domesticated South American camelid, widely used as a meat and pack animal by Andean cultures since the Pre-Columbian era. Llamas are social animals and live with others as a herd. Their wool is soft ...
s of the Andes. Stenobarc animals are those with lesser ability to endure a range of differences in altitude, such as rabbits,
mountain goat The mountain goat (''Oreamnos americanus''), also known as the Rocky Mountain goat, is a hoofed mammal endemic to mountainous areas of western North America. A subalpine to alpine species, it is a sure-footed climber commonly seen on cliffs an ...
s,
sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to domesticated ...
, and
cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...
s. Among
domesticated animals This page gives a list of domesticated animals, also including a list of animals which are or may be currently undergoing the process of domestication and animals that have an extensive relationship with humans beyond simple predation. This includ ...
, yaks are perhaps the highest dwelling animals. The
wild Wild, wild, wilds or wild may refer to: Common meanings * Wild animal * Wilderness, a wild natural environment * Wildness, the quality of being wild or untamed Art, media and entertainment Film and television * ''Wild'' (2014 film), a 2014 A ...
herbivores A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
of the Himalayas such as the
Himalayan tahr The Himalayan tahr (''Hemitragus jemlahicus'') is a large even-toed ungulate native to the Himalayas in southern Tibet, northern India, western Bhutan and Nepal. It is listed as Near Threatened on the IUCN Red List, as the population is declini ...
,
markhor The markhor (''Capra falconeri'') is a large ''Capra'' species native to Central Asia, the Karakoram, and the Himalayas. It is listed on the IUCN Red List as Near Threatened since 2015. The markhor is the national animal of Pakistan, where i ...
and chamois are of particular interest because of their ecological versatility and tolerance.


Rodents

A number of
rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...
s live at high altitude, including
deer mice Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the reindee ...
,
guinea pig The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy (), is a species of rodent belonging to the genus '' Cavia'' in the family Caviidae. Breeders tend to use the word ''cavy'' to describe the ...
s, and rats. Several mechanisms help them survive these harsh conditions, including altered
genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...
of the
hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyt ...
gene in guinea pigs and deer mice. Deer mice use a high percentage of fats as metabolic fuel to retain carbohydrates for small bursts of energy. Other physiological changes that occur in rodents at high altitude include increased
breathing rate The respiratory rate is the rate at which breathing occurs; it is set and controlled by the respiratory center of the brain. A person's respiratory rate is usually measured in breaths per minute. Measurement The respiratory rate in humans is me ...
and altered morphology of the lungs and heart, allowing more efficient
gas exchange Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a ...
and delivery. Lungs of high-altitude mice are larger, with more capillaries, and their hearts have a heavier right ventricle (the latter applies to rats too), which pumps blood to the lungs. At high altitudes, some rodents even shift their
thermal neutral zone Endothermic organisms known as homeotherms maintain internal temperatures with minimal metabolic regulation within a range of ambient temperatures called the thermal neutral zone (TNZ). Within the TNZ the basal rate of heat production is equal to ...
so they may maintain normal
basal metabolic rate Basal metabolic rate (BMR) is the rate of energy expenditure per unit time by endothermic animals at rest. It is reported in energy units per unit time ranging from watt (joule/second) to ml O2/min or joule per hour per kg body mass J/(h·kg). Pro ...
at colder temperatures. The deer mouse (''
Peromyscus maniculatus ''Peromyscus maniculatus'' is a rodent native to eastern North America. It is most commonly called the eastern deer mouse; when formerly grouped with the western deer mouse (''P. sonoriensis''), it was referred to as the North American deermou ...
'') is the best studied species, other than humans, in terms of high-altitude adaptation. The deer mice native to Andes highlands (up to ) are found to have relatively low hemoglobin content. Measurement of food intake, gut mass, and cardiopulmonary organ mass indicated proportional increases in mice living at high altitudes, which in turn show that life at high altitudes demands higher levels of energy. Variations in the
globin The globins are a superfamily of heme-containing globular proteins, involved in binding and/or transporting oxygen. These proteins all incorporate the globin fold, a series of eight alpha helical segments. Two prominent members include myogl ...
genes ( α and β-globin) seem to be the basis for increased oxygen-affinity of the hemoglobin and faster transport of oxygen. Structural comparisons show that in contrast to normal hemoglobin, the deer mouse hemoglobin lacks the hydrogen bond between α1Trp14 in the A
helix A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined helic ...
and α1Thr67 in the E helix owing to the Thr67
Ala Ala, ALA, Alaa or Alae may refer to: Places * Ala, Hiiu County, Estonia, a village * Ala, Valga County, Estonia, a village * Ala, Alappuzha, Kerala, India, a village * Ala, Iran, a village in Semnan Province * Ala, Gotland, Sweden * Alad, S ...
substitution, and there is a unique hydrogen bond at the α1β1 interface between residues α1Cys34 and β1Ser128. The Peruvian native species of mice ('' Phyllotis andium'' and ''
Phyllotis xanthopygus The yellow-rumped leaf-eared mouse (''Phyllotis xanthopygus'') otherwise known as the Patagonian leaf-eared mouse is a species of rodent in the family Cricetidae and order Rodentia. It is the most widespread member of the genus. Description ''Ph ...
'') have adapted to the high Andes by using proportionately more carbohydrates and have higher oxidative capacities of
cardiac muscle Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle th ...
s compared to closely related native species residing at low-altitudes (), ('' Phyllotis amicus'' and '' Phyllotis limatus''). This shows that highland mice have evolved a metabolic process to economise oxygen usage for physical activities in the hypoxic conditions.


Yaks

Among
domesticated animals This page gives a list of domesticated animals, also including a list of animals which are or may be currently undergoing the process of domestication and animals that have an extensive relationship with humans beyond simple predation. This includ ...
, yaks ('' Bos grunniens'') are the highest dwelling animals of the world, living at . The yak is the most important domesticated animal for Tibet highlanders in
Qinghai Province Qinghai (; alternately romanized as Tsinghai, Ch'inghai), also known as Kokonor, is a landlocked province in the northwest of the People's Republic of China. It is the fourth largest province of China by area and has the third smallest pop ...
of China, as the primary source of
milk Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digest solid food. Immune factors and immune-modula ...
, meat and
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
. Unlike other yak or
cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult ma ...
species, which suffer from hypoxia in the Tibetan Plateau, the Tibetan domestic yaks thrive only at high altitude, and not in lowlands. Their physiology is well-adapted to high altitudes, with proportionately larger lungs and heart than other cattle, as well as greater capacity for transporting oxygen through their blood. In yaks,
hypoxia-inducible factor Hypoxia-inducible factors (HIFs) are transcription factors that respond to decreases in available oxygen in the cellular environment, or hypoxia. They are only present in parahoxozoan animals. Discovery The HIF transcriptional complex w ...
1 (''HIF-1'') has high expression in the
brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...
, lung and
kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...
, showing that it plays an important role in the adaptation to low oxygen environment. On 1 July 2012 the complete genomic sequence and analyses of a female domestic yak was announced, providing important insights into understanding mammalian
divergence In vector calculus, divergence is a vector operator that operates on a vector field, producing a scalar field giving the quantity of the vector field's source at each point. More technically, the divergence represents the volume density of t ...
and adaptation at high altitude. Distinct gene expansions related to
sensory perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system ...
and energy metabolism were identified. In addition, researchers also found an enrichment of protein domains related to the extracellular environment and hypoxic stress that had undergone positive selection and rapid evolution. For example, they found three genes that may play important roles in regulating the bodyʼs response to hypoxia, and five genes that were related to the optimisation of the energy from the food scarcity in the extreme plateau. One gene known to be involved in regulating response to low oxygen levels, ADAM17, is also found in human Tibetan highlanders.


Humans

Over 81 million people live permanently at high
altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...
s (>) in
North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''north ...
, Central and
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...
, East Africa, and
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
, and have flourished for
millennia A millennium (plural millennia or millenniums) is a period of one thousand years, sometimes called a kiloannum (ka), or kiloyear (ky). Normally, the word is used specifically for periods of a thousand years that begin at the starting point (ini ...
in the exceptionally high mountains, without any apparent complications. For average human populations, a brief stay at these places can risk mountain sickness. For the native highlanders, there are no adverse effects to staying at high altitude. The physiological and genetic adaptations in native highlanders involve modification in the oxygen transport system of the blood, especially molecular changes in the structure and functions of
hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyt ...
, a protein for carrying oxygen in the body. This is to compensate for the low oxygen environment. This adaptation is associated with developmental patterns such as high
birth weight Birth weight is the body weight of a baby at its birth. The average birth weight in babies of European descent is , with the normative range between . On average, babies of South Asian and Chinese descent weigh about . As far as low birth weigh ...
, increased
lung volumes Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle. The average total lung capacity of an adult human male is about 6 litres of air. Tidal breathing is normal, resting breath ...
, increased breathing, and higher resting metabolism. The
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...
of Tibetans provided the first clue to the
molecular evolution Molecular evolution is the process of change in the sequence composition of cellular molecules such as DNA, RNA, and proteins across generations. The field of molecular evolution uses principles of evolutionary biology and population genetics ...
of high-altitude adaptation in 2010. Genes such as ''
EPAS1 Endothelial PAS domain-containing protein 1 (EPAS1, also known as hypoxia-inducible factor-2alpha (HIF-2α)) is a protein that is encoded by the ''EPAS1'' gene in mammals. It is a type of hypoxia-inducible factor, a group of transcription factor ...
'', '' PPARA'' and ''
EGLN1 Hypoxia-inducible factor prolyl hydroxylase 2 (HIF-PH2), or prolyl hydroxylase domain-containing protein 2 (PHD2), is an enzyme encoded by the ''EGLN1'' gene. It is also known as Egl nine homolog 1. PHD2 is a α-ketoglutarate/2-oxoglutarate-depe ...
'' are found to have significant molecular changes among the Tibetans, and the genes are involved in hemoglobin production. These genes function in concert with transcription factors,
hypoxia inducible factors Hypoxia-inducible factors (HIFs) are transcription factors that respond to decreases in available oxygen in the cellular environment, or hypoxia. They are only present in parahoxozoan animals. Discovery The HIF transcriptional complex w ...
(''HIF''), which in turn are central mediators of red blood cell production in response to oxygen metabolism. Further, the Tibetans are enriched for genes in the disease class of human reproduction (such as genes from the '' DAZ'', '' BPY2'', '' CDY'', and '' HLA-DQ'' and ''
HLA-DR HLA-DR is an MHC class II cell surface receptor encoded by the human leukocyte antigen complex on chromosome 6 region 6p21.31. The complex of HLA-DR (Human Leukocyte Antigen – DR isotype) and peptide, generally between 9 and 30 amino acids in ...
'' gene clusters) and biological process categories of response to
DNA damage DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA d ...
stimulus and
DNA repair DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA da ...
(such as '' RAD51'', ''
RAD52 RAD52 homolog (S. cerevisiae), also known as RAD52, is a protein which in humans is encoded by the ''RAD52'' gene. Function The protein encoded by this gene shares similarity with ''Saccharomyces cerevisiae'' Rad52, a protein important for DNA ...
'', and ''
MRE11A Double-strand break repair protein MRE11 is an enzyme that in humans is encoded by the ''MRE11'' gene. The gene has been designated ''MRE11A'' to distinguish it from the pseudogene ''MRE11B'' that is nowadays named ''MRE11P1''. Function This ge ...
''), which are related to the adaptive traits of high infant birth weight and darker skin tone and, are most likely due to recent local adaptation. Among the Andeans, there are no significant associations between ''EPAS1'' or ''EGLN1'' and hemoglobin concentration, indicating variation in the pattern of molecular adaptation. However, ''EGLN1'' appears to be the principal signature of evolution, as it shows evidence of positive selection in both Tibetans and Andeans. The adaptive mechanism is different among the Ethiopian highlanders. Genomic analysis of two ethnic groups, Amhara and Oromo, revealed that gene variations associated with hemoglobin differences among Tibetans or other variants at the same gene location do not influence the adaptation in Ethiopians. Instead, several other genes appear to be involved in Ethiopians, including '' CBARA1'', ''
VAV3 Guanine nucleotide exchange factor VAV3 is a protein that in humans is encoded by the ''VAV3'' gene. This gene is a member of the VAV gene family. The Vav (protein), VAV proteins are guanine nucleotide exchange factors (GEFs) for Rho family GTPas ...
'', ''
ARNT2 Aryl hydrocarbon receptor nuclear translocator 2 is a protein that in humans is encoded by the ''ARNT2'' gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." me ...
'' and '' THRB'', which are known to play a role in HIF genetic functions. The EPAS1 mutation in the Tibetan population has been linked to
Denisovan The Denisovans or Denisova hominins ) are an extinct species or subspecies of archaic human that ranged across Asia during the Lower and Middle Paleolithic. Denisovans are known from few physical remains and consequently, most of what is known ...
-related populations. The Tibetan haplotype is more similar to the Denisovan haplotype than any modern human haplotype. This mutation is seen at a high frequency in the Tibetan population, a low frequency in the Han population and is otherwise only seen in a sequenced Denisovan individual. This mutation must have been present before the Han and Tibetan populations diverged 2750 years ago.


Birds

Birds have been especially successful at living at high altitudes. In general, birds have physiological features that are advantageous for high-altitude flight. The respiratory system of birds moves oxygen across the pulmonary surface during both inhalation and exhalation, making it more efficient than that of mammals. In addition, the air circulates in one direction through the parabronchioles in the lungs. Parabronchioles are oriented perpendicularly to the
pulmonary arteries A pulmonary artery is an artery in the pulmonary circulation that carries deoxygenated blood from the right side of the heart to the lungs. The largest pulmonary artery is the ''main pulmonary artery'' or ''pulmonary trunk'' from the heart, and ...
, forming a cross-current gas exchanger. This arrangement allows for more oxygen to be extracted compared to mammalian concurrent gas exchange; as oxygen diffuses down its concentration gradient and the air gradually becomes more deoxygenated, the pulmonary arteries are still able to extract oxygen. Birds also have a high capacity for oxygen delivery to the tissues because they have larger hearts and cardiac stroke volume compared to mammals of similar body size. Additionally, they have increased vascularization in their flight muscle due to increased branching of the
capillaries A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...
and small muscle fibres (which increases surface-area-to-volume ratio). These two features facilitate oxygen diffusion from the blood to muscle, allowing flight to be sustained during environmental hypoxia. Birds' hearts and brains, which are very sensitive to arterial hypoxia, are more vascularized compared to those of mammals. The
bar-headed goose The bar-headed goose (''Anser indicus'') is a goose that breeds in Central Asia in colonies of thousands near mountain lakes and winters in South Asia, as far south as peninsular India. It lays three to eight eggs at a time in a ground nest. It ...
(''Anser indicus'') is an iconic high-flyer that surmounts the Himalayas during migration, and serves as a model system for derived physiological adaptations for high-altitude flight.
Rüppell's vulture Rüppell's vulture (''Gyps rueppelli''), also called Rüppell's griffon vulture, named after Eduard Rüppell, is a large bird of prey, mainly native to the Sahel region and East Africa. The current population of 22,000 is decreasing due to loss ...
s,
whooper swan The whooper swan ( /ˈhuːpə(ɹ) swɒn/) (''Cygnus cygnus''), also known as the common swan, pronounced ''hooper swan'', is a large northern hemisphere swan. It is the Eurasian counterpart of the North American trumpeter swan, and the type speci ...
s,
alpine chough The Alpine chough (), or yellow-billed chough (''Pyrrhocorax graculus'') is a bird in the crow family, one of only two species in the genus '' Pyrrhocorax''. Its two subspecies breed in high mountains from Spain eastwards through southern Europ ...
, and
common crane The common crane (''Grus grus''), also known as the Eurasian crane, is a bird of the family Gruidae, the cranes. A medium-sized species, it is the only crane commonly found in Europe besides the demoiselle crane (''Grus virgo'') and the Siberian ...
s all have flown more than above sea level. Adaptation to high altitude has fascinated
ornithologists __NOTOC__ This is a list of ornithologists who have articles, in alphabetical order by surname. See also :Ornithologists. A * John Abbot – US * Clinton Gilbert Abbott – US * William Louis Abbott – US * Joseph H. Acklen – US *Humayun Ab ...
for decades, but only a small proportion of high-altitude species have been studied. In Tibet, few birds are found (28
endemic species Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
), including cranes,
vulture A vulture is a bird of prey that scavenges on carrion. There are 23 extant species of vulture (including Condors). Old World vultures include 16 living species native to Europe, Africa, and Asia; New World vultures are restricted to North and ...
s, hawks,
jays A jay is a member of a number of species of medium-sized, usually colorful and noisy, passerine birds in the Crow family, Corvidae. The evolutionary relationships between the jays and the magpies are rather complex. For example, the Eurasian m ...
and
geese A goose ( : geese) is a bird of any of several waterfowl species in the family Anatidae. This group comprises the genera '' Anser'' (the grey geese and white geese) and ''Branta'' (the black geese). Some other birds, mostly related to the she ...
. The Andes is quite rich in bird diversity. The
Andean condor The Andean condor (''Vultur gryphus'') is a giant South American Cathartid vulture and is the only member of the genus ''Vultur''. Found in the Andes mountains and adjacent Pacific coasts of western South America, the Andean condor is the larg ...
, the largest bird of its kind in the
Western Hemisphere The Western Hemisphere is the half of the planet Earth that lies west of the prime meridian (which crosses Greenwich, London, United Kingdom) and east of the antimeridian. The other half is called the Eastern Hemisphere. Politically, the te ...
, occurs throughout much of the Andes but generally in very low densities; species of
tinamou Tinamous () form an order of birds called Tinamiformes (), comprising a single family called Tinamidae (), divided into two distinct subfamilies, containing 46 species found in Mexico, Central America, and South America. The word "tinamou" come ...
s (notably members of the genus ''
Nothoprocta ''Nothoprocta'' is a genus of birds belonging to the tinamou family Tinamidae. They inhabit scrubland, grassland and open woodland in western South America, particularly in the Andes. They are poor fliers and spend most of their time on the gro ...
''),
Andean goose The Andean goose (''Chloephaga melanoptera'') is a species of waterfowl in tribe Tadornini of subfamily Anserinae.HBW and BirdLife International (2021) Handbook of the Birds of the World and BirdLife International digital checklist of the bird ...
, giant coot,
Andean flicker The Andean flicker (''Colaptes rupicola'') is a South American species of woodpecker. It is found in grassland, shrubland and '' Polylepis'' woodland at altitudes of in the Puna ecoregion. Together with the campo flicker and ground woodpecker ...
, diademed sandpiper-plover, mountain parakeet,
miners A miner is a person who extracts ore, coal, chalk, clay, or other minerals from the earth through mining. There are two senses in which the term is used. In its narrowest sense, a miner is someone who works at the rock face; cutting, blasting, ...
, sierra-finches and diuca-finches are also found in the highlands.


Cinnamon teal

Evidence for adaptation is best investigated among the Andean birds. The
water fowl The Anatidae are the biological family of water birds that includes ducks, geese, and swans. The family has a cosmopolitan distribution, occurring on all the world's continents except Antarctica. These birds are adapted for swimming, floating ...
s and cinnamon teal ('' Anas cyanoptera'') are found to have undergone significant molecular modifications. It is now known that the α-hemoglobin subunit gene is highly structured between elevations among cinnamon teal populations, which involves almost entirely a single non-synonymous amino acid base-pair substitution, substitution at position 9 of the protein, with asparagine present almost exclusively within the low-elevation species, and serine in the high-elevation species. This implies important functional consequences for oxygen affinity. In addition, there is strong divergence in body size in the Andes and adjacent lowlands. These changes have shaped distinct morphological and genetic divergence within South American cinnamon teal populations.


Ground tits

In 2013, the molecular mechanism of high-altitude adaptation was elucidated in the Tibetan ground tit (''Pseudopodoces humilis'') using a draft genome sequence. Gene family expansion and positively selected gene analysis revealed genes that were related to cardiac function in the ground tit. Some of the genes identified to have positive selection include ''ADRBK1'' and ''HSD17B7'', which are involved in the adrenaline response and steroid, steroid hormone biosynthesis. Thus, the strengthened endocrine system, hormonal system is an adaptation strategy of this bird.


Other animals

alpine climate, Alpine Tibet hosts a limited diversity of animal species, among which snakes are common. A notable species is the Euophrys omnisuperstes, Himalayan jumping spider, which can live at over of elevation. There are only two endemic reptiles and ten endemic amphibians in the Tibetan highlands. ''Gloydius himalayanus'' is perhaps the geographically highest living snake in the world, living at as high as in the Himalayas.


Plants

Many different plant species live in the high-altitude environment. These include perennial grasses, Cyperaceae, sedges, forbs, cushion plants, mosses, and lichens. High-altitude plants must adapt to the harsh conditions of their environment, which include low temperatures, dryness, ultraviolet radiation, and a short growing season. Trees cannot grow at high altitude, because of cold temperature or lack of available moisture. The lack of trees causes an ecotone, or boundary, that is obvious to observers. This boundary is known as the tree line. The highest-altitude plant species is a moss that grows at on
Mount Everest Mount Everest (; Tibetic languages, Tibetan: ''Chomolungma'' ; ) is List of highest mountains on Earth, Earth's highest mountain above sea level, located in the Mahalangur Himal sub-range of the Himalayas. The China–Nepal border ru ...
. The sandwort ''Arenaria bryophylla'' is the highest flowering plant in the world, occurring as high as .


See also

* Aeroplankton * Alpine plant * Altitude * Altitude sickness * Animals in space *
Ethiopian Highlands The Ethiopian Highlands is a rugged mass of mountains in Ethiopia in Northeast Africa. It forms the largest continuous area of its elevation in the continent, with little of its surface falling below , while the summits reach heights of up to . ...
* Fauna of the Andes * Health threat from cosmic rays * Human spaceflight * Plants in space * Skylab Medical Experiment Altitude Test *
Tibetan Plateau The Tibetan Plateau (, also known as the Qinghai–Tibet Plateau or the Qing–Zang Plateau () or as the Himalayan Plateau in India, is a vast elevated plateau located at the intersection of Central, South and East Asia covering most of the ...


References

{{reflist, 33em Respiratory physiology Evolutionary biology Selection Zoology Biological records