Why Don’T Humans Have Hair All Over Their Bodies?

Have you ever wondered why you don't have thick hair covering your whole body like a dog, cat or gorilla does? Humans aren't the only mammals with sparse hair. Elephants, rhinos and naked mole rats also have very little hair. It's true for some marine mammals, such as whales and dolphins, too.

Scientists think the earliest mammals, which lived at 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's the advantage of not growing your own fur coat? I'm a biologist who studies the genes that control hairiness in mammals. Why humans and a small number of other mammals are relatively hairless is an interesting question. It all comes down to whether certain genes are turned on or off.

Hair benefits

Hair and fur have many important jobs. They keep animals warm, protect their skin from the sun and injuries and help them blend into their surroundings. They even assist animals in sensing their environment. Ever felt a tickle when something almost touches you? That's your hair helping you detect things nearby. Humans do have hair all over their bodies, but it is generally sparser and finer than that of our hairier relatives. A notable exception is the hair on our heads, which likely serves to protect the scalp from the sun.

(The author is associated with University of Pittsburgh)