Kurt Stein has a famous book, Hair: A Fun History of Humanity, which is an interesting cultural history of hair. He has a famous saying in it: human beings grow hair to survive, and fade hair in order to survive better.
Modern humans do not have thick body hair, which is indeed a very unique phenomenon, although the density of hair follicles throughout the human body is not much different from the density of hair follicles on apes.
Why human body hair disappears
One of the most popular hypotheses about why humans evolved so little body hair is that when upright hominids migrated from forests to the savannah's hot sun, they had to give up their hair to stay cool.
But the question is why other animals that live in the scorching sun of the savannah don't give up their hair? What if you think that the hot sun can cause fatal damage to primitive people with body hair? As a result, primitive humans can only adapt to the hot sun of the savannah by sacrificing individuals with thick body hair, then African creatures such as lions and elephants should also shed their hair, but lions and other animals still have hair.
To this day, there is no particularly perfect answer to this question, when we lose hair, our skin loses protection from the sun. Scientists believe that when humans lose their hair, that's when their skin gets darker, because dark skin protects you from the sun better than light skin.
Geneticist Alans Rogers specializes in genetics (the set of instructions your body inherits from your parents). According to his research, the genes (directives) to make dark skin were created just before 1 million years ago. So it can be assumed that this was also when our ancestors began to lose hair.
That is to say, the only thing that human beings can confirm at present is that about one or two million years ago, human ancestors lived in the African savannah, and the stout species of Australopithecus, African species and Homo erectus coexisted at the same time, and the degradation of body hair began from this moment.
There is also a question, in the process of evolution, after the hair of the whole body of human beings has faded, why are hair, pubic hair and armpit hair left?
Why do humans still have hair, pubic hair and armpit hair?
We need to know that hair is divided into three types: terminal hair, milli hair and long hair, of which terminal hair is divided into long hair and short hair. All hairs that can be permanently removed are terminal and hairless.
Long hair: hair, beard, pubic hair, armpit hair.
Short hair: eyebrows, nose hair, eyelashes, external auditory canal hair.
Hairless: The hair on the face, neck, torso, and limbs is hairless. Well, even if your leg hair is longer than your eyebrows, it's hairless.
Hair: The white soft and fine hair on the body surface of the fetus.
In the process of our human evolution, human beings have not lost their hair in a strict sense, and the hair of our body has only changed to form a existence.
All we shed was the long hairs that covered the whole body, which then became milli and short hairs. Only hair, beard, pubic hair, and armpit hair retain long hair.
The reason for this, scientists believe that humans retain hair because thick hair can form an air barrier between the scalp and the surface of the hair with higher temperature, when the person is in a higher temperature environment, the hair will absorb heat, but there is an air barrier gap between the hair and the scalp, which can make the temperature of the scalp not so high and maintain a relatively low temperature state.
Therefore, highly curly hair will bring greater air barrier, which can bring better protection to the head and better circulation of air.
This view can also explain why African hair is curly and not prone to hair loss, the earliest human hair is likely to be highly curly, and other types of hair may have slowly changed after the evolution of human life tools, all the result of natural selection.
Many people think that the existence of eyebrows is to protect the eyes, let sweat beads and raindrops detour, so that they do not flow into the eyes, but this is actually more of the role of the eyelashes, and the nerves under the eyelashes are more sensitive, than the eyebrows can block more things. For example, if we touch our eyelashes with our hands, our eyes will immediately close, but we will not respond when we touch our eyebrows.
A study by the University of York found that the brow spine of early Homo sapiens was more prominent, with the eyebrows located at the lower edge of the brow ridge. Neanderthals, Denisovans, Heidelbergens, Dali, Taurushan, and Maba people found in China are all representatives of early Homo sapiens. They had better social systems, and scholars at York University believe that movable eyebrows played an important role in communication, so this excellent trait continued from Homo erectus to Homo sapiens.
Using highly flexible eyebrows to express emotions helped early humans convey messages of approval, compassion, and more. Scientists believe this is crucial for human survival, because with this ability to communicate, humans can work together instead of struggling alone in the wild. This may also be the reason why modern humans have flatter foreheads and sharper eyebrows than early humans.
And armpit hair and pubic hair are left behind for two reasons, one is to spread the message of sexual maturity, and the other is to reduce the wear and tear on their parts when we exercise, and protect the armpits and private parts from harm. As a result, armpit and pubic hair stop growing to a certain length.
For human men, beards are hairy, and scientists believe that this is also the result of sexual selection, scientists speculate that although full beards were a burden for men in ancient times, they could attract the opposite sex by showing off their beards, and it is because of this that beards were preserved during human evolution.
summary
Of course, these are the theoretical hypotheses put forward by scientists, and what the truth is, scientists need to use more fossils to find the truth hidden behind.