Why are humans not as hairy as other mammals?

A comprehensive answer to this question has been provided by biologists from the University of Pittsburgh (USA). They remind us that humans are not the only mammals with sparse hair. Elephants, rhinoceroses, and naked mole rats also have very little hair. Not to mention marine mammals like whales and dolphins. According to the scientists, prehistoric mammals that lived during the time of the dinosaurs were quite hairy. However, over hundreds of millions of years, a small group of these mammals, including humans, evolved to have less hair. Biologists studying the genes that control hairiness in mammals understand what determines the level of hair coverage in this class of animals. It turns out that it all comes down to whether certain genes are turned on or off.

The Benefits of Abundant Hair

Fur serves many important functions. It keeps animals warm, protects their skin from the sun and injuries, and allows them to blend into their environment. Moreover, dense hair helps animals sense their surroundings, including detecting nearby objects. In fact, humans also have hair growing all over their bodies, but it is generally fine and sparse compared to their furrier counterparts in the animal kingdom. A notable exception is the hair on our heads, which protects us from the sun. In adult humans, the thick hair that grows under the arms and in the intimate areas likely reduces skin friction and aids in cooling through sweat evaporation. Thus, hair can be quite beneficial. There must be a significant evolutionary reason for why humans have lost so much of it.

Why Did Humans Lose Hair?

The story began around 7 million years ago when humans and chimpanzees took different evolutionary paths. Scientists have several theories explaining why humans lost their hair. We have significantly more sweat glands than chimpanzees and other mammals. Sweating helps us keep our bodies cool. When sweat evaporates from our skin, it removes thermal energy from the body. This cooling system was likely critical for early human ancestors living in the hot African savanna.

Of course, many furry mammals still thrive in hot climates today. Ancient humans could have hunted such animals by exhausting them through long runs in the heat, as reported by Science Alert. Humans didn’t need to run faster than the animals they hunted; they just had to track their prey and keep going until the quarry overheated and became too tired to continue. The ability to sweat profusely without a thick layer of hair made humans more resilient.

Genes That Control Hairiness

To better understand hairiness in mammals, the university team compared genetic information from 62 species, ranging from humans to armadillos, dogs, and squirrels. By mapping the DNA of various species, the researchers focused on the genes associated with the retention or loss of body hair. They discovered that humans still possess all the genes necessary for a full coat of hair; they are simply muted or turned off. Overall, genes can cause remarkable changes in hair growth. The monster in the famous tale by Gabrielle-Suzanne Barbot de Villeneuve, “Beauty and the Beast” (1740), is covered in thick fur. This may seem like fantasy, but in real life, members of the species Homo sapiens can occasionally grow a lot of hair all over their bodies. Of course, not by choice. This condition is known as hypertrichosis, or “werewolf syndrome.” It is extremely rare. In the 1500s, a Spaniard named Petrus Gonsalvus was born with hypertrichosis. As a child, he was sent in a cage, like an animal, as a gift to Henry II of France. Soon, the king realized that Petrus was just like any other person and that he could be educated. Eventually, Petrus married a woman. This story is the inspiration behind the tale of “Beauty and the Beast.”

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