Humans belong to mammals, and belong to the primates, and most of the mammals we usually see are hairy, primates are also like this, such as monkeys, orangutans, baboons, etc., but the human body is white and pure, in addition to the head, armpits, crotches and other places, other parts usually only have a little sweat hair, why is there so little human body hair?
In fact, there are many theories about the degradation of human hair, such as heat dissipation theory, water ape theory, etc., there is no conclusive conclusion at present, "heat dissipation theory" believes that the human body has shed body hair in order to better dissipate heat, "water ape said", that is still in the era of apes, people have a period of time in the water and land amphibious life, but more people think that human use of clothing to keep warm is the most reliable way to fade body hair.
When human beings learn to wear clothes to keep warm, they are not so afraid of the cold, when there is no clothes to wear, if there is no hair on the body, human beings can not survive the cold winter anyway, even if they only live in the tropics, the temperature difference between the hot summer and the continuous rainy days is also very large, when the wise human knows how to use leaves and animal skins to keep the body warm and cold, the body hair began to fade the process.
The process is roughly like this, in the era of the great apes, human hair is still relatively large, but in the face of weather and climate change, the body's perception of heat and cold will make people make some remedial actions, such as when the human body feels cold, apes (or primitive humans) have known to wrap the body with leaves or animal skins to protect the body from the cold, then whenever the body feels cold, this activity repeatedly will make the body think that the hair is no longer so important, so it also began the stage of hair removal.
So in this way, the more human beings who know how to use the things around them to protect their bodies, the faster their hair will recede, but the less hair, the more people need to use leaf animal skins or other things to keep warm, and gradually people will learn to wrap leaves, animal skins or other things that can be made into clothing in the village, then when primitive humans have such clothes to keep warm, the hair all over the body is useless, so human beings will gradually fade into today's appearance.
In fact, to this day, some people living in the primitive tribal state of the tropics still use this method to keep warm and cold, and some people have a small amount of body hair genes, such as some Caucasian people have a lot of body hair, and many people will grow body hair on their chests.
There is also such a phenomenon in life, that is, when the weather is getting colder from summer to autumn, if you always wear very little clothes, the body often feels cold, then after a period of time, you will find that the hair on the legs or arms will become thicker, and the growth will become frightened, which is actually a stress response of the human body to the environment, when the body feels cold, it will make a warm remedy on its own, but today's human beings have been unable to grow so much body hair like in ancient times. In autumn and winter, relying on body hair to keep warm can be cold!