Why don’t humans have hair all over their bodies? A biologist explains our lack of fur

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Why don’t humans have hair all over their bodies like other animals? – Murilo, 5 years old, Brazil

Have you ever wondered why you don’t have thick hair covering your entire body like a dog, cat or gorilla does?

Humans aren’t the only mammals with thinning hair. Naked elephants, rhinos, and mole rats also have very little hair. This is also true for some marine mammals, such as whales and dolphins.

Scientists believe that the first mammals, which lived during the time of the dinosaurs, were quite hairy. But over hundreds of millions of years, a small handful of mammals, including humans, evolved to have less hair. What is the advantage of not growing your own fur coat?

I am a biologist who studies the genes that control hair growth in mammals. Why humans and a small number of other mammals are relatively hairless is an interesting question. It all depends on whether certain genes are activated or deactivated.

Benefits for hair

Hair and fur perform many important tasks. They keep animals warm, protect their skin from sun and injury, and help them blend into their surroundings.

They even help animals perceive their surroundings. Have you ever felt a tickle when something almost touches you? It’s your hair that helps you detect nearby objects.

Humans have hair all over our bodies, but it is generally sparser and finer than that of our hairier relatives. A notable exception is the hair on the head, which probably serves to protect the scalp from the sun. In adult humans, the thicker hair that develops under the arms and between the legs likely reduces skin friction and contributes to cooling by dispersing sweat.

Hair can therefore be very beneficial. There must be a strong evolutionary reason for people to lose so much.

Why humans lost their hair

The story begins around 7 million years ago, when humans and chimpanzees took different evolutionary paths. Although scientists can’t know for sure why humans became less hairy, we have some solid theories regarding sweating.

Humans have many more sweat glands than chimpanzees and other mammals. Sweating keeps you cool. As sweat evaporates from your skin, heat energy is carried away from your body. This cooling system was likely crucial for early human ancestors, who lived in the hot African savannah.

Of course, many mammals living in warm climates are currently covered in fur. Early humans were able to hunt these kinds of animals by tiring them out during long chases in the heat – a strategy known as persistent hunting.

Humans didn’t need to be faster than the animals they hunted. They just had to keep going until their prey was too hot and tired to flee. Being able to sweat a lot, without having thick hair, made this endurance possible.

Genes that control hair growth

To better understand hairiness in mammals, my research team compared genetic information from 62 different mammals, from humans and armadillos to dogs and squirrels. By aligning the DNA of all these different species, we were able to target genes linked to hair maintenance or loss.

Among the many discoveries we’ve made, we’ve learned that humans still carry all the genes needed to grow beautiful hair – they’re just muted or turned off.

In the story of “Beauty and the Beast,” the Beast is covered in thick fur, which may seem like pure fantasy. But in real life, some rare conditions can cause a lot of hair to grow all over the body. This condition, called hypertrichosis, is very unusual and has been called “werewolf syndrome” because of the appearance of people who have it.

In the 1500s, a Spaniard named Petrus Gonsalvus was born with hypertrichosis. As a child, he was sent in an iron cage as an animal to Henry II of France as a gift. It was not long before the king realized that Petrus was like any other person and could be educated. In time, he married a woman, which inspired the story of “Beauty and the Beast.”

Although you’ll probably never meet someone with this rare trait, it shows how genes can lead to unique and surprising changes in hair growth.

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This article is republished from The Conversation, an independent, nonprofit news organization that brings you trusted facts and analysis to help you make sense of our complex world. It was written by: Maria Chikina, University of Pittsburgh

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Maria Chikina receives funding from the NIH and NSF.