The British zoologist and human behaviorist Desmond Morris called humans "naked apes", so what is the reason for human hair loss, and why do they retain pubic hair, armpit hair and hair?
Hair is mainly composed of keratin, which is easily broken down, and it is difficult to leave traces in history, and the answer to hair can only be inferred from some substances that are closely related to hair and can be continued or left behind, such as genes.
At the end of the twentieth century, the son of the German biologist Mark Stogin brought back from school a note by the teacher that read:
Some students at the school have head lice, so be careful. Head lice, a kind of small lice, live on people and make people itch.
Mark Stogin had the inspiration that lice on the human body rely on human body temperature and hair to live, leaving the human body will soon die, so by studying the genes of lice, it is possible to roughly infer the time when the human hair fades.
Our ancestors were also a species with hair all over the body, hair is like a "continent" that runs through together, lice can wander from head to foot, full genetic exchange, so the whole body lice genes are roughly the same at that time.
Today there are three types of lice: pubic lice, body lice, and head lice. Because most of the human body's hair has faded, just like most of the land gradually sinks to the bottom of the sea, and finally only part of the isolated island is left, the lice on the hair in different positions are isolated for a long time, and each has evolved into different species.
The emergence of body lice stems from the fact that humans wear clothes, and head lice have evolved antennae and claws that can be attached to clothing fibers. In other words, clothing is like an ocean connecting the islands, and body lice are new species that have evolved into the head lice "going to the sea" of the head island, so the time of clothing can be inferred, but this is not the focus today.
Scientists have studied the genes of the three lice extensively, calculating through the "molecular biological clock" that the head lice and the pubic lice parted ways about 1.2 million years ago, that is, the time when the human hair disconnected, that is, the body began to shed hair at least 1.2 million years ago.
According to modern evolutionary theory, our ancestors wandered the African savannah 1.2 million years ago. Looking at the wild animals that exist in the African savannah today, most of them are covered with hair, and the same is true for orangutans who are close to humans and are in Africa, so why are humans so special?
This is the end result of the constant trade-offs between the pros and cons in the environment as humans evolved. All living things must constantly absorb energy from the outside world in order to survive, and at the same time constantly radiate energy outward. Hair has a thermal insulation effect, which can prevent heat loss, which means that it can reduce predation and has a greater survival advantage, so even in the hot African savannah animals are still wearing "fur coats".
This evolution has a drawback, when the internal heat is too much, species with poor heat dissipation ability can not quickly dissipate heat, it is easy to "heat stroke" fainting, and even life-threatening, so lions on the African savannah spend most of their time hiding in the shade. Poor heat dissipation means that most animals can only perform "100-meter sprints" and cannot perform marathon exercises.
5 million years ago, the ancestors of human beings were arboreal apes with fruits and leaves as the main food, due to the climate change caused by plate movement, the forest became a savanna, and the ancient apes had to survive on the ground, they had no fangs, sharp claws, could not quickly explode speed and strength to kill prey, and could only use endurance to hunt.
Today, some ancient tribes still follow this hunting skill - persistent hunting, after selecting the prey, constantly tracking and chasing until the prey faints to the ground due to internal heat, and then goes up to "mend a knife" and then dismembers or directly resists the whole animal.
This is a game of heat dissipation ability, the hair becomes shorter and evolves rapid sweat dissipation ability to make humans go farther and farther on the road of endurance advantage, and eventually only retain some of the necessary hair, becoming a naked ape.
East Africa, the origin of human beings, is located near the equator, which is the basic condition for human hair shedding, and if it were near the poles, humans would certainly not embark on this path. Human head is covered by the scorching sun, running wildly on the grassland to chase prey, limbs continue to move, rapid metabolism caused by internal heat can rely on the perspiration system to dissipate heat, but the amount of head movement is less, more importantly to prevent the scorching sun and the body's heat transfer upwards to invade the scalp, because the brain is the most important part of the human body.
At present, the mainstream theory believes that the reason for the retention of hair is that a "hollow" can be formed between the hairs, isolating heat, preventing the brain from heating up and isolating heat transfer, so the hair is retained.
The axillary hair is located in a relatively closed position, which is not conducive to the elimination of sweat, but the sweat glands are more developed, the armpit hair can inhibit the growth and reproduction of microorganisms, and some scientists believe that the armpit hair can be less friction when running.
Regarding pubic hair, some scientists believe that the "skin" here is more tender, and the hair can prevent sunburn, and at the same time, it also plays a certain anti-friction role when breeding. Other scientists believe that this is convenient for judging whether the opposite sex has reached the age of reproduction, which is a sign of maturity.
Under the evolution of "hairless", although we need to lose more heat, but also from the outside world to obtain more energy, so as to have a higher ability to survive, hairless, hairless is the two sides of the double-edged sword, there is no distinction between strength and weakness, only which is more suitable, which is easier to survive, which is a way of survival under the "power of the chicken without hands".