The adaptation of cold and heat to humans is part of the broader adaptability of Homo sapiens . Adaptation in humans can be physiological, genetic, or cultural, which allows people to live in various climates. There has been a great deal of research done on developmental adjustments, acclimatization, and cultural practices, but less research on genetic adaptations for cold and hot temperatures.
The human body is always working to remain in homeostasis. One form of homeostasis is thermoregulation. The body temperature varies with each individual, but the mean internal temperature is 37.0 ° C (98.6 ° F). Stress from extreme external temperatures can cause the human body to die. When the body becomes hypothermic, the core temperature drops to 35 ° C, (95 ° F, 95 ° F). Hyperthermia occurs when the body's core temperature rises above 37.5-38.3 ° C (99.5-100.9 ° F). This temperature generally causes death. Humans have adapted to live in this extreme climate primarily through culture and technology, such as the use of clothing and shelter.
Video Cold and heat adaptations in humans
Origin of cold and hot adaptation
Modern humans emerged from Africa some 40,000 years ago. Evidence suggests that modern culture may originate as well. Modern humans spread to Europe and defeated the Neanderthals, suggesting that early modern humans were quite able to adapt to life in various climates. This is supported in the variability selection hypothesis proposed by Richard Potts, which says that human adaptation comes from long-term environmental change.
Ecogeographic rule
Bergmann's rule states that subspecies of endothermic animals living in cold climates have larger bodies than subspecies that live in warm climates. Individuals with larger bodies are more suited to colder climates because larger bodies produce more heat because they have more cells, and have a smaller surface area compared to smaller individuals, which reduces heat loss. A study by Frederick Foster and Mark Collard found that Bergmann's rule can be applied to humans when latitudes and temperatures between groups are very different.
Allen's rule is a biological rule that says the limb endotherm is shorter in cold climates or longer in hot climates. Long legs affect the body surface area, which helps with thermoregulation. Shorter limbs help to save heat, while longer limbs help to get rid of heat. Marshall T. Newman argues that this can be observed in Eskimo, which has shorter legs than others and is built laterally.
Maps Cold and heat adaptations in humans
Physiological adaptation
The ambient air temperature affects how much energy investment the human body has to make. The temperature that requires the least amount of energy investment is 21 ° C (69.8 ° F). The body controls its temperature through the hypothalamus. Thermoreceptors in the skin send signals to the hypothalamus, which indicates when vasodilation and vasoconstriction should occur.
Cold
The human body has two methods of thermogenesis, which produce heat to raise the core body temperature. The first is shivering, which occurs in people who are not clothed when the air temperature is about 25 ° C (77 ° F). This is limited by the amount of glycogen available in the body. The second is no shivering, which occurs in brown adipose tissue.
Heat
The only mechanism of the human body to cool itself is by the evaporation of sweat. Sweat occurs when the air temperature is above 28 Â ° C (80 Â ° F) and the body fails to return to normal internal temperature. Evaporation of sweat helps cool the blood under the skin. This is limited by the amount of water available in the body, which can cause dehydration.
Acclimatization
When humans are exposed to a particular climate for a long time, physiological changes occur to help individuals adapt to hot or cold climates. It helps the body save energy.
Cold
Eskimos have more blood flowing into their extremities, and at warmer temperatures, than people living in warmer climates. A 1960 study on Indian Alacaluf showed that they had a resting metabolic rate of 150 to 200 percent higher than the white controls used. Lapps do not have an increase in metabolic rate during sleep, unlike people who are unfamiliar. Australian aborigines undergo a similar process, in which the body cools but the metabolic rate does not increase.
Hot
Humans in Central Africa have lived in the same tropical climate for at least 40,000 years, meaning that they have the same thermoregulation system.
A study conducted on the South African Bantus shows that Bantus has a lower sweat rate than the accustomed and non-acclimatized white. Similar research conducted on indigenous Australians produced similar results, with indigenous populations having a much lower level of sweat than whites.
Culture
Social adaptation allows early modern humans to occupy an environment with a temperature that is drastically different from that in Africa. (Potts 1998). Culture allows humans to extend their reach to areas that should be uninhabitable.
Cold
Humans have been able to occupy very cold areas by creating a microclimate, such as clothing, buildings, and fire manipulation. Using energy to create technology like a furnace further allows the occupation of cold environments.
Australian Aborigines wear only genital coverings for clothing, but research shows that the warmth of the fire they build is enough to keep the body from fighting heat loss through chills. Eskimos use well-insulated homes designed to move heat from energy sources to living areas, which means that the average indoor temperature for the Eskimo beach is 10 to 20 ° C (50-68 ° F).
Hot
Humans live in hot climates, both dry and humid, and have done so for thousands of years. Selective use of clothing and technological inventions such as air conditioning allow humans to thrive in hot climates.
One example is the Arab Chaamba, living in the Sahara Desert. They wear garments that trap air between skin and clothing, preventing ambient air temperature to reach the skin.
Genetic adaptation
There is little research done in the genetics behind adaptation to heat and cold pressure. The data show that certain parts of the new human genome were chosen for the recent time. Research on gene-cultural interactions has been successful in linking agricultural tolerance and lactose. However, much of the evidence of the relationship between culture and selection has not been proven.
References
Source of the article : Wikipedia
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