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Why the human head has more hair than other parts

   According to foreign media reports, humans are "freaks" among mammals. Except for hippos and naked mole rats, almost all other mammals have fur on their bodies. Except for head hair, humans are almost naked and hairless. Why? Except for the head, most parts of human beings are hairless?

  Mark Pegel, an evolutionary biologist at the University of Reading in the United Kingdom, said that first of all, it is important to understand why mammals have fur. Fur can keep animals warm in cold nights and protect them from sun burns during the day. Human ancestors can Most of the hair is lost because they have a unique ability to light a fire, keep warm in sleep, and wear clothes.

  This will explain why our human ancestors can survive without hair, but it cannot explain why the hair gradually disappears over time. In fact, the hairless feature gives humans a certain evolutionary advantage. According to Pegel, there are three main theories. Can explain this human evolutionary advantage.

  First of all, thick fur may cause ancient humans to overheat under the hot noon sun. Pegel said: "In the hot season, if you wear a thick fur coat on the African savannah, then you must It’s going to be very hot. Wouldn’t it be okay to take this coat off? Humans have gradually achieved this in the long course of evolution." In addition, modern humans have evolved to have more sweat glands than their close relatives in primates. Keeping long body hair is likely to be soaked by sweat, which makes it difficult for sweat to evaporate, and it is difficult for the body to cool down.

  However, the so-called "body cooling hypothesis" cannot fully explain the distribution pattern of human hair growth. For example, why men have more body hair than women. It is worth noting that in addition to the hands, feet, lips and nipples, the human body also covers With small colorless hairs. Hormones produced during puberty turn these colorless fine hairs into longer, colored terminal hairs. But sometimes in addition to the disheveled body hair, the head is the densest hair area of ​​the human body.

  Secondly, the second explanation theory is called the "aquatic ape hypothesis theory." This theory believes that ancient humans lived in water for a long time. When they swim, their bodies will be soaked with more hair and will not easily surface, so they Most of the body hair is gradually lost, leaving only the head as the densest hair area. However, so far there is no conclusive evidence that humans have lived in water for a long time during the evolutionary process, so Pegel believes that the hypothesis is not very credible and cannot explain why humans lose a lot of fur after leaving the water environment.

  In 2003, Pager published a research report and put forward the third theory, the ectoparasite hypothesis. Ectoparasites refer to the parasites that live outside the host's body. These parasites include lice, fleas, etc., which cause cross-species disease. The main cause of illness and death. Ectoparasites may be less attracted to hairless skin tissues and are easier to remove when the hair tissue is less covered. Conversely, the less hairy tissues of the body, the fewer the number of ectoparasites. This may be human The dominant choice for evolutionary survival.

  If hair is hurt, why do we still grow hair?

  As a biped, we walk upright with our head directly exposed to the sun. The African region close to the equator is the birthplace of human evolution, where the sun is very strong, and having dense hair can help humans avoid body heat. Pegg Er said: "Hair in Africa is like a built-in

  summer hat." Pegel said: "Hair also helps the human body retain heat at night. Compared with other parts of the body, our brain is relatively small, but the brain's The metabolism is very active, this activity generates heat, and the hair can isolate this concentrated heat."

  Sexual choice can also play a role. People can shape different hair and show their unique charm. Ancient humans may also be like this. Hair can be used as a unique way to show the charm of the opposite sex. Hair usually cannot be directly turned into fossils, so it cannot be preserved intact. Archaeologists have no direct evidence of ancient human hair, except that mummies in places such as Egypt and Peru will preserve corpse hair intact. The researchers observed and analyzed modern aborigines isolated from the outside world and found that they also had their own unique hairstyles, suggesting that their ancestors also had them. Pegel pointed out that this special hair care may help attract partners of the opposite sex. Not only do we grow hair, but we also use some form of hairstyle to attract the opposite sex.


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