Why are we the only hairless primate?
There are about 5,000 kinds of mammals in the world. Among the many mammals, humans may be the most unusual, because compared to other mammals with furry appearance, humans seem to be naked.
Take primate close relatives, if other primates are compared to ordinary cats, humans are like a group of hairless cats.
Why do humans lose their body hair? Or why do humans retain the "hairless" feature?
At present, there are three viewpoints in the scientific community to explain this problem. All viewpoints have one thing in common, that is, less and less hair is good for humans.
Picture: Comparison of hairless Sphinx cat and ordinary cat
Water Ape Hypothesis
The water ape hypothesis believes that between 6 to 8 million years ago, the ancestors of modern human apes had a semi-aquatic lifestyle. They generally foraged in shallow water, and fewer hairs can reduce the time when they move in the water.Resistance.
Moreover, this ancient gene exists in people’s hair genes today: for example, the growth direction of leg hair, hair, sweat hair, etc. is consistent with the direction of water flow.
This explanation is not unreasonable, because animals whose ancestors were aquatic but themselves are terrestrial animals do exist. Elephants are a good example.
The chemical characteristics of a tooth fossil once indicated that at least one species of Proboscis lived in water, and it was a close relative of ancient elephants.
This can explain why zebras, lions, giraffes, etc. that live in the tropics all have hair, but elephants are bare.
At the same time, there is another similarity between humans and elephants in that they have subcutaneous fat. Other primates don’t have it. This is very similar to marine animals.
Although the water ape hypothesis can explain why humans lost their hair, there is no fossil evidence that human ancestors were aquatic.
The dry grassland hypothesis should be familiar to many people. This theory believes that human ancestors lost their hair in order to adapt to the high temperature of the grassland, because the forests they lived in before were relatively cool.
Most mammals are warm-blooded animals, and proper body temperature can ensure the normal operation of the body, but the environmental temperature is variable, so they need to adjust their own temperature.
There are two ways to adjust the temperature: heating when the environment is cold, and heat dissipation when the environment is hot, which is why heat dissipation is very important for animals.
The reason why the ancestors of humans walked out of the forest was not for fun, but because of the drought, Africa's forests were greatly reduced, and they did not have enough habitat.
Picture: Thermal imaging of human body
At the same time, the plants they depend on have also decreased with the decrease of forests, but the number of herbivores has begun to increase as the forests become grasslands.
It takes a lot of energy to find plants that they liked to eat before, so they slowly turned to eating the meat of these herbivores.
Hunting requires running, and this is something that human ancestors rarely did before. Their body functions cannot withstand the effects of a lot of running, such as what we call heat dissipation.
But the opposite of this theory is that there is a problem: losing hair is good for heat dissipation but not good for heat preservation. Isn’t heat preservation more important than heat?
The third hypothesis is the parasite hypothesis. The reason why human ancestors are "naked" is to prevent the spread of parasites that like to parasite in the hair.
Furry hair is usually a natural shelter for parasites such as ticks and lice. They not only make people itchy and uncomfortable, but also carry viruses or bacteria.
This will cause the human body to suffer from some protozoan diseases, such as malaria, sleeping sickness, Lyme disease, etc., which will lead to a decline in body function and even death.
This explanation believes that the hair of human ancestors degenerates after they have learned to live, because this can make up for the loopholes in the steppe hypothesis.
We may all know lice, where do lice usually appear? It is indeed hair, which makes the parasite hypothesis a certain degree of correctness.
In addition, there is a mammal that seems to support this theory, and that is the naked mole rat.
Picture: naked mole rat
Naked mole rats live underground in groups. If they have hair, it must be a parasite paradise. For this reason, they have lost their hair.
Then how to solve their heat preservation problem? Of course they don’t make a fire, but the closed activity space makes their heat preservation problem much easier.
Once it evolves in a "hairless" way, it will be affected by sexual selection, and one of the sexes will choose a spouse accordingly.
Smooth, transparent skin is likely to be a sign of good health, just like the tail of a peacock, which can also explain why women are naturally less hairy than men.
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