Among all terrestrial mammals, humans are considered an anomaly because no animal is as bare as humans, so why do humans shed their body hair and when do they shed it?
Trying to find direct evidence to determine when human body hair fades is a very difficult task, but the evolution of a small animal that side-steps this mystery for us is the louse. Lice are a parasite on the human body, mainly in the hairy parts of the body, such as in the hair and pubic hair, but the lice in the hair and the lice in the pubic hair are not the same, one is "head lice" and one is "pubic lice".
Broadly speaking, head lice and pubic lice look similar, but head lice are darker and pubic lice are lighter, and head lice are elongated, while pubic lice are equal in length and width, which is clearly the result of the evolution of one organism in two different directions.
Why do head lice and pubic lice evolve in different directions? Because there are differences in the living environment of the two. In the period when the human body was covered with body hair, lice could roam around the body through the hair, but after the human body hair was removed, the hair was no longer connected to other parts of the hair in small handfuls, and the two places were isolated from each other, and after the loss of genetic communication, the lice in different living environments began to evolve in different directions.
It is not difficult for modern science to determine the time of differentiation between head lice and pubic lice; all that is needed is a genetic comparison of the two to arrive at a rough result.
Scientists have finally determined that the differentiation between head lice and pubic lice was 1.2 million years ago, and by extension, the time when humans shed their hair should also be 1.2 million years ago. So why did humans shed their body hair? The time when humans and apes parted ways on the evolutionary path can be traced back to about 3 million years ago, the different evolutionary direction made human habits gradually changed, humans began to eat mainly vegetarian to meat and vegetarian evolution, and to eat meat, it is necessary to hunt.
For human ancestors, hunting is not a problem, because humans are very good at running.
Yes, human running speed is not very fast, but the human endurance is unmatched by other animals. The process of human ancestors to capture prey is a contest of endurance, although other animals are fast, but it is difficult to last, because running will accumulate heat in the body, the heat has not had time to dissipate, humans catch up again, so they have to continue to run, and eventually these animals will be too much heat accumulation, physical exhaustion and fall to the ground. On the contrary, humans, after the removal of body hair, humans have an unparalleled ability to dissipate heat, humans through sweating can continue to efficiently discharge body heat, so they can continue to run for a long time.
Since humans choose to shed their body hair, why is it not shed cleanly?
The human body is not completely bare, in our head, armpits and pubic area have a small amount of hair, why they are preserved? Human beings shed body hair to better heat, and retain the hair is also to avoid overheating the body. The top of the head is the highest part of the body, is directly facing the sun, the existence of hair can well protect the top of the head and the back of the shoulders from the direct sun, you know that long time running under the hot sun is very easy to sunburn.
Hair exists to protect against the sun, so what is the use of the small handfuls of hair in the armpits and pubic area?
Many modern women will eliminate the underarm hair, thinking that this thing is superfluous, but in fact it is not. I don't know if you have noticed, after the armpit hair is removed, the armpit seems to become more prone to sweating and odor? This is not an illusion, because without the isolation of the armpit hair, the skin under the armpit will be close together repeatedly friction, hot summer is particularly easy to sweat, so remove the armpit hair is a unique contemporary thing, because when we go to work and home to stay in the air-conditioned room, and when you go out to stay in the air-conditioned car, if not, remove the armpit hair may make you into embarrassment, and pubic hair and the role of the armpit hair is probably In addition, there is a small amount of hair that grows around the anus also has the same effect.