Let scientists scratch their heads. When you go to the library one day to find the answer, you will find that apart from musk oxen, human beings are almost the only animal whose hair has been growing. Why on earth is this? But you can't find the answer from the library shelves at all, because no one has been able to solve the mystery so far. In the past few years, scientists have become more and more interested in studying human hair. A short article published in the American journal Evolutionary Anthropology by Arthur Newfield, a physiologist at Northwestern University, and Glenn Conroy, an anthropologist at Washington University in St. Louis, was the first person to discuss this issue. They pointed out that other mammals' hair will automatically stop growing when it reaches a certain length, but human hair will continue to grow. They asked in the article: "Have you ever seen chimpanzees comb their hair? Or have you ever seen any long-haired animals need a haircut? " Of course not. Why on earth can human hair keep growing? At present, people don't know much about this problem. Hair grows on the surface of human body except palm and sole. Human hair can be divided into soft hair and hard hair according to its thickness and hardness. Soft hair, commonly known as hair, is soft and light in color and spreads all over the skin surface; Bristles are thick and hard and grow in some parts of the human body, such as hair. For adults, under the control of complex hormone mechanism, these two types of hair can expand into a variety of hairs, such as eyebrows, eyelashes, armpit hair, beard and so on. Both smooth hair and tiny toe hair can grow at the rate of 1 ~ 1.5 cm per month, and the hair stops growing for a very short time before falling off. Different parts of the body have different hair lifetimes, which can determine their final length. For example, leg hair can last for about 2 months, armpit hair can last for 6 months, but hair can last for 6 years or even longer. When hair grows to a certain period, it begins to fall off and be replaced. The replacement of human hair is not seasonal like that of mammals, but often falls off and is gradually replaced throughout life. According to statistics, there are10 ~ 200,000 hairs, including 80 ~14,000 hairs in the head, 20,000 hairs in the trunk and limbs, and 30 ~ 120 hairs fall off every day. The life span of different parts of hair is different: the life span of hair is 2 ~ 5 years; Beard for 2 ~ 3 years; Axillary hair 1 ~ 2 years; Pubic hair 1 ~ 1.5 years (the life span of beard, armpit hair and pubic hair is only 7 ~ 10 months); The life span of eyebrows and eyelashes is 3 ~ 5 months. In addition to natural shedding at the end of life, hair may also fall off due to poisoning, disease or violence. Gene mutation may be the main reason. As for how to control hair growth, there are still many uncertainties, and scientists have not solved some mysteries. But the growth of hair may be related to countless genes. Moreover, even if only one gene changes, it will have a great impact on hair growth. Take Angora rat as an example. Its long hair is related to a gene mutation called FGF5, which is a protein that prevents hair growth. Nuefeld and Conroy believe that the reason for the sustained growth of human hair may be that FGF5 or similar gene mutation has lost the function of inhibiting hair growth. Another possibility is that the gene of 10 main keratin (an insoluble and hard protein substance, which is the main structural component of hair, nails, horns and hooves) contained in hair is constantly copied. Scientists have pointed out that nine kinds of keratin in humans, chimpanzees and gorillas are almost the same, but the tenth kind-PHI-HHAA is obviously different. Although for humans, phi-hHaA is a pseudogenetic factor (that is, a part of DNA of deoxyribonucleic acid, which is similar to genetic factor, but has no genetic function and cannot synthesize protein), it is a mutant protein in other primates. In 200 1 year, Helmilita Venter of the German Cancer Research Center published his discovery: this gene mutation appeared 240,000 years ago. Which is more attractive, short hair or long hair? Short hair has many advantages over long hair: first, it is more conducive to health care, because long hair is more likely to breed parasites; In addition, it is also beneficial to regulate body temperature. Short hair can make human ancestors better adapt to the climate from jungle to savanna. Some people even think that keeping short hair is the adaptation of ancestors to life by the water. Darwin believes that sexual orientation is the key: people with short hair look more attractive than those with long hair, so there are more descendants, more people and fewer people with long hair. Although short hair has many advantages, the fact is that human beings prefer long hair, which has become thicker during the evolution. You know, it takes more energy to keep your hairstyle and get rid of parasites. The latest view is that hair is the best stage for people to show their social status because it needs so much care. Proper hairstyle is an important part of social interaction, which can reveal your class, social circle and communication ability. If all the above are correct, then the conclusion is clear: human hair grows only for decoration. Alison Giuly, a primate expert at the University of Sussex, said, "This is very correct. Neat hair will make the same kind think that someone is willing to tidy his hair. This requires not only good social relations and enough time, but also ingenuity. " This may explain why people with sparse and unkempt hair are considered homeless, crazy or untouchable. The above explanation seems far-fetched, but Curry believes that primates have been doing this for a long time. Grooming is a way of communication among primates. Many primates have very complicated hairstyles to show their health, status and population. She cited many examples, including African baboons, Amazonian tamarind monkeys, Emperor tamarind monkeys and Indian macaques. Sirrah believes that for human ancestors, hair style is not only a part of individuals, but also related to their status in the ethnic group, which is very obvious in some tribes. Earlier this year, Cronic wine, which was discovered in Mises swamp 2,300 years ago, apparently used original hair gel to make its hair stand on end. He also believes that since human beings began to evolve 20,000 years ago, hairstyles, like human badges, have gone through a long process. But so far, no fossils of hair accessories have been found to confirm this view. But the hairstyles of some of the oldest human statues are indeed decorated. Venus 23,000 years ago is an example. Her creator didn't give her obvious facial features, but gave her a beautiful hairstyle. Similarly, there is the oldest three-dimensional human figure unearthed in France-the bronze statue of Lady Blaise Mbo 25,000 years ago. She has beautiful shoulder-length hair.