It is said that humans and chimpanzees have a common ancestor, but one has a protruding hair and a protruding upper and lower jaw, and the other seems to be naked and retracted. The huge difference between humans and chimpanzees has led many people to suspect the blood relationship between humans and chimpanzees, but genes have given direct evidence that humans and chimpanzees have a large number of genetic similarities, which strengthens the confidence of scientists.
The reproduction of organisms is based on populations, and reproduction is actually the combination of reproductive cells of both sexes, and the chromosomes in germ cells are from parents, although there may be a few mutations in genes, but most genes are still inherited from parents. In other words, reproduction is the basis of evolution. Species have a variety of genes, but there is a certain similarity, similarity comes from heredity, from those genes that are not mutated, diversity comes from mutation, mutation to a certain extent is evolution, long biological differences, even in humans can not find an exact same.
Human body hair is also a puzzle in evolution, land mammals all have thick hair, marine life due to large environmental differences are calculated separately. Land mammals are still full of hair even in hot Africa, but this limits their ability to run, cheetah running speed can be said to be the highest on land, but continuous running for hundreds of meters or minutes is not enough, because the heat dissipation is too poor, the body heat accumulates rapidly during exercise, and the overheating of internal organs may lead to organ failure.
Marine life is another model, marine mammals almost all have thick subcutaneous fat, in general, the sea temperature is lower than the atmospheric temperature, but the sea temperature due to the ocean circulation is relatively stable, only the temperature of the surface sea water varies greatly at different latitudes. The subcutaneous fat of marine mammals helps to reduce heat dissipation, whale fat in ancient times is an important fuel, medicine, can be used for lighting or medicine, modern and related industries, mainly concentrated in Japan and Northern European countries.
However, only humans, mammals, seem to have no hairs on their bodies, only in some important parts. But if you look closely, in addition to the palms of the hands and feet, most of the skin of human beings actually has hairs on the whole body, but our hair is very different from other land mammals, most of our hair is thin and short, and the hair of land mammals such as chimpanzees is thick and long. Thick hair helps keep you warm, and this is a very simple experience for humans to make clothes from animal furs during migration.
But why have humans lost their hair? How did humans carry it around the world after they lost their hair and then migrated to the far north near the Arctic Circle? Speaking of this, many people have taken out the theory of evolution, believing that no hair is not conducive to survival, but in fact, Darwin's theory of evolution and modern biological evolution emphasize the adaptability of organisms, rather than a specific trait. The hair looks sparse and does not have a good effect on warmth, but other ways to keep warm can be taken.
About 1.14 million years ago, humans gradually lost their hair, which is based on the evolution of body lice in humans. There is only one type of lice on the human body, similar to chimpanzees, because originally humans also had thick hairs all over the body, and body lice could be moved throughout the human body. But later human hair gradually degenerated, only the top of the head, private parts and other places on the body has thick hair, armpit sweat, not suitable for lice to live, until after putting on the clothes, the hair on the clothes helps the lice parasitism.
According to the information revealed by genes, human hair degeneration was about 1.14 million years ago, when the lice on the human body began to differentiate, and now the body lice and pubic lice and head lice gradually produce reproductive isolation. It's not just the hair that decides to stay warm, it can be some other external means. According to modern scientific analysis (ancient human remains in the middle of the charcoal pile), humans have mastered the use of flames since more than 2 million years ago, and they also know how to find warm caves to live in. Flames can be warmed, and warm caves can be sheltered from the wind and cold.
It is equivalent to the human ancestors using this method to adapt to the temperature difference between day and night, while the demand for food leads to another change in the human ancestors. In the warm jungles of East Africa, trees transpire during the day and the air is warm, plants have respiration at night, and the relatively bare surface also radiates heat, so warmth is not the first need, and the need for food and reproduction is the highest level. At that time, human ancestors had just walked upright, and their running ability was slightly poor, so they evolved a relatively good endurance, and the key to endurance was the degeneration of hair and the appearance of sweat glands.
Hair becomes thin and short can accelerate the air flow on the surface of the body, sweat glands sweat evaporation, both ways can accelerate the dispersion of heat, so that human endurance increases, much stronger than many beasts of prey, humans have also successfully adapted to the jungle environment, from omnivorous (staple plants) to meat (staple meat or berries, tree branches and leaves), food abundance has brought about the reproduction of the population, the increase in the number of populations has led to fierce intra-population survival competition, so some ancient humans began to migrate to colder places such as Asia and Europe. In this process, the role of animal fur was observed and he learned to make clothes.
As for the hair left behind, there are two main functions, on the one hand, it is to resist the harm of nature, and on the other hand, it may have the influence of sexual selection. The hair on the top of the human head can avoid the exposure of the scalp, more direct sunlight in Africa, the top of the head is most and most evenly exposed to direct sunlight, the hair can resist the exposure of the sun, avoid dry cracking of the skin, the hair of the armpits and private parts on the one hand is a diversion of sweat, can also increase the friction during exercise; there are also differences in the hair traits of men and women, the male exercise is greater, the hair in the armpits and other places is more exuberant.
In terms of sexual selection, after putting on clothing, the identification of the opposite sex mainly depends on the second sex characteristics, including hair, throat knots, etc., and different populations are also different, Europeans have strong hair, and even hair on the chest, Asia and Africa are thinner, and the characteristics of hair are also very different, which helps different human populations to identify the same kind.