According to legend, the ancient Greek philosopher Plato proposed that "man is an animal that walks on two feet and has no feathers (hair)", whether this statement is correct or not, it shows that people at that time have pointed out that the characteristics of the vast majority of people are that most areas of the body do not have thick body hair.
Throughout the various human primate relatives, such as chimpanzees and orangutans, almost all parts of the body are covered by dense body hair, except for a few parts such as the face and palms. This shows that humans should have had very thick body hair in the early days, but this layer of equipment gradually faded due to various reasons in the process of evolution.
What's in the book? (Photo: Yitu.com).
Animal hair.
Hair is a derived structure of animals** and is mainly composed of keratin. Current research suggests that reptile scales, bird feathers, and mammalian body hair share a common origin.
The aesthetics of texture and color, feel it.
Photo: Shutterstock).
Almost all mammals on land have body hair, and its effects are roughly as follows:
First of all, the most basic function of animal body hair is to keep warm. Polar bears and other animals living in extremely cold environments form an insulation layer through their dense body hair, which effectively blocks the invasion of cold air from the outside and keeps their body temperature stable.
Secondly, some animals have succeeded in camouflage in their natural environment with the help of the color of their body hair. For example, the snow leopard's coat color is similar to that of alpine snow, making it easier to approach its prey when hunting; Arctic foxes are grayish-black in the summer, but grow snow-white body hair in the winter. The body hair of these animals not only provides them with good camouflage, but also gives them a unique advantage when hunting or escaping predators.
Snow Leopard: "I've hid it, you can find it".
Photo: Shutterstock).
Third, body hair plays a role in the social interaction of animals. For example, when a cat encounters danger or wants to intimidate the other person, its body hair will stand on end, creating a "fried hair" effect.
There are also body hairs that can sense changes in the outside world, and the most familiar to the public is the cat's sensory hair that can help hunting. But in addition to cats, many creatures such as seals and foxes have sensory hair.
You've got me, you've got it all, wow.
Photo: Shutterstock).
Finally, there is another role that many people may not have noticed: defense.
Although the thick fur of animals during the fight has a more or less protective effect, there are also animals that take the defensive function of body hair to the extreme. The hedgehog's thorn is a specialized body hair, also made of keratin, which is essentially the same thing as the hair on the human body.
In addition, the carapace of pangolins is a special type of hair, except that these hairs grow into sheets, forming a hard, tough shell. This unique piece of armor provides superior protection for pangolins in case of danger.
Overall, the shape and color of the animal's body hair shows the magic of nature. From a visual point of view, this diversity presents us with a rich and colorful ecosystem. From a functional and adaptive point of view, animal body hair is a masterpiece of natural selection, providing key support for animals to survive and reproduce in a variety of environments.
The aesthetics of nature are indeed superlative.
Photo: Shutterstock).
Human body hair.
The ancestors of humans separated from their chimpanzee ancestors about 6 million years ago, and since then the two species have followed two completely different evolutionary paths.
But when did humans lose most of their body hair? This question has puzzled scholars for many years. It wasn't until later that people gradually turned their attention to another creature.
Apes say goodbye (Photo: Shutterstock).
Lice are known to be a class of parasites that live on the surface of animals, mainly settling on hair-rich parts of the host's body. Their locomotion is mainly crawling, and because lice lack the ability to fly, they have difficulty moving over long distances. Therefore, the ecological habits of different species and different parts of the same species show certain differences.
At present, we have found three kinds of lice in humans: head lice (parasitic on hair), body lice (parasitic on clothing) and pubic lice (parasitic on **) Theoretically, these three lice have a common ancestor, and this type of lice can move freely in ancient humans when they have not lost most of their hair.
Write "lice" for you
As ancient humans gradually lost most of their body hair, the lice that originally parasitized the head and crotch could no longer move freely to other parts, and the lice on the head and crotch began to develop unique traits and differentiated. Later, as humans put on clothing, some lice moved to the host's clothing, causing a new differentiation of the lice population, forming a subgroup adapted to reproduce and parasitize in clothing.
The scalp is numb, and I am afraid not to watch it (Photo: YouTube).
According to this theory, scholars have found through molecular biology that head lice and pubic lice diverged about 1.2 million years ago; Body lice differentiated from head lice about 180,000 years ago.
Based on this, it is now generally believed that humans began the path of hair removal at least 1.2 million years ago. Some of the theoretical explanations that scholars have come up with for this reason include:
In order to adapt to the hot and empty environment of Africa, and in order to adapt to the long distance of hunting and chasing, some people gradually evolved less body hair and more sweat glands, which greatly improved the survival ability of these ancient humans and won the competition.
Dense body hair becomes a paradise for a variety of parasites, increasing the risk of disease;
Humans learned to use fire and became less dependent on body hair......
It may be that under one or more reasons, humans have lost most of their body hair, but they still retain their hair, eyebrows, beard, armpit hair, **, etc.
We now know that the body hair that the human body retains plays a role to a greater or lesser extent: hair, for example, prevents direct sunlight from hitting the scalp and protects the head from ultraviolet rays, thus protecting the brain, the most important organ in the human body. Eyebrows can prevent sweat, rain, etc. from flowing down the forehead directly into the eyes.
Probably the most significant facial difference between men and women is the beard of men. There is still no consensus on why men retain beards during evolution. The main hypotheses are:
Attract the opposite sex. Just like a male peacock opening the screen to court, a man's beard is also a charm that attracts women.
Protects the head and neck. Since ancient times, men have often fought in the process of defending their families, etc., and in the process, thick beards can protect the fragile mandible and neck, and reduce damage.
In addition, there are two places where almost everyone, both men and women, have thicker hair: armpits and **.
Scholars believe that these two places are the parts where the hands and legs are often rubbed, and the hair can reduce friction and avoid damage; Secondly, the beginning of the growth of ** and axillary hair indicates sexual maturity; Finally, armpit hair has another effect: it can retain armpit odor and make body odor more persistent.
Although the strong armpit odor in modern society can make people feel uncomfortable and embarrassed, in ancient times, it was like a top perfume, representing the unique charm of adults and the hormones of walking.
It's bald, and it's stronger.
Adults mainly have two types of hair: cuì hair and terminal hair. Vellus hair is hair that is widely distributed in almost all ** except for the palms and soles of the feet. The terminal hair is mainly hair, eyebrows, eyelashes, beard, armpit hair and **.
There is no more obvious body hair on a human body than hair. For thousands of years, people have had different attitudes towards hair, and even rose to the level of cultural and identity identity.
Hair can also show aesthetics, for example
Each person has about 100,000 hairs, which are made up of three parts: hair follicles, hair roots, and hair shafts. The hair growth cycle usually lasts from 2 to 6 years, and it mainly goes through three stages: anagen, degenitive, and telogen. During the anagen phase, hair is constantly growing from the hair follicles; In the catagen phase, the hair gradually stops growing and is ready to fall out; Finally, the telogen phase begins, where the hair follicles temporarily remain dormant, waiting for a new growth cycle to begin.
This cyclical process is the key to maintaining the normal state of the hair, and it is also the natural law of hair growth and shedding. Under normal conditions, hair can grow about 1cm in one month, but it is subject to genetic and endocrine regulation. At the same time, according to the different metabolism of the human body, the cycle of hair growth and loss is also different.
Although it is normal for hair to grow and fall out, if too much hair falls out and no new hair grows, "baldness" can occur. Today, the balding population has begun to show a trend of getting younger.
Life is not easy Most "baldness" is medically androgenetic alopecia, also known as seborrheic alopecia. The reason why it is called "androgenetic alopecia" is because this type of hair loss is closely related to androgens.
Studies have shown that dihydrotestosterone, an androgen, can cause hair follicles to shrink, causing hair to be deprived of nutrients, become thin and soft, and fall out more easily. In addition, it moves hair follicles from anagen to telogen phase, increasing the likelihood of hair loss.
Because androgen levels are much higher in men than in women, "baldness" is more common in men. According to statistics, the proportion of androgenetic alopecia among men over 18 years old in China is one-fifth, and that of women is one-twentieth.
Different means to the same end? ▼
However, some studies have found that whether it is hair loss or no hair loss, the difference in dihydrotestosterone levels in the body is not too big. Therefore, the current academic community tends to believe that the hair follicle epithelial cells of people with hair loss have more androgen receptors, making them more sensitive to androgens and more susceptible to stimulation.
There are a number of medications available for hair loss, such as finasteride (for adult men only), a 5-reductase inhibitor that blocks the conversion of testosterone to dihydrotestosterone, thus stopping hair loss.
Finasteride (Photo: Shutterstock).
In addition, baldness is also closely related to genetics, and irregular lifestyle, unhealthy diet, and mood swings may also cause hair loss. Therefore, maintaining a healthy mindset and healthy life in daily life also has a positive effect on the prevention of hair loss.
Of course, if you can't avoid hair loss eventually, you can also take a hair transplant.
Nowadays, the function of hair has gone beyond the original setting of the natural world, and has also assumed the role of culture and civilization. Especially for the most conspicuous hairs on the whole body, such as hair and beard, different periods and different countries have different aesthetics.
But for humanity as a whole, we have been on the path of evolution, and it is not known whether there will be a hair in one place that will disappear in a thousand years, or a new hair in another place.
References: 1 buffoli b, rinaldi f, labanca m, et al. the human hair: from anatomy to physiology. int j dermatol. 2014;53(3):331-341.
2.One out of every five adult males is "topped out"! How is it**? Popular Science China Released on 2023-10-28.
3.Nina Jablonsky. If hair removal is an evolutionary product, why do you still grow hair? Dong Wei [Translation].
The content of this article is provided by the author and does not necessarily represent the position of the Earth Knowledge Bureau
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