Why Humans Aren't Covered In Fur Explained By A Biologist

Have you ever thought about why you don’t wake up one morning covered in a thick fur coat, just like a dog, cat, or gorilla? You’re not alone in being relatively hairless: elephants, rhinos, and naked mole rats also have very little hair, and many marine mammals, such as whales and dolphins, have almost none.

Yet, if you rewind the clock to the age of dinosaurs, the earliest mammals were probably quite furry. Over hundreds of millions of years, a small handful of species shed most of their fur. What could be the upside of losing your natural coat?

It all comes down to switches in our DNA and the demands of life on the African savanna. A biologist who studies the genes that control hair growth in mammals has discovered why people, and just a few other mammals, ended up with less hair.

First, consider all the jobs hair and fur do. They trap heat to keep you warm when it’s cold, shield your skin from sunburns and scrapes, and help animals blend into their surroundings.

The tiny hairs on your face and arms act like an early warning system: have you ever felt a tickle when something brushes past you? That’s your hair sensing the world around you.

Some mammals sport lush fur coats, while others barely have a hair to speak of.

Humans still have hair covering their bodies, but it’s usually finer and more spread out than that of most mammals. The thick hair on your head probably evolved to protect your scalp from sun damage.

The coarse hair under your arms and around your groin helps reduce friction and spreads sweat, which cools you down. Despite these benefits, evolution sometimes trades one advantage for another, and in our case, the ability to sweat freely proved more valuable than a full fur coat.

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About seven million years ago, our ancestors split from the chimpanzee branch. Chimpanzees kept their dense fur, but early humans gradually lost most of theirs. One primary reason appears to be sweating.

Humans possess far more sweat glands than any other primate or most mammals. As sweat evaporates, it carries heat away from the body, providing an efficient cooling system. In the scorching heat of the African savanna, this ability to shed excess heat would have been critical.

Early humans leveraged this cooling advantage through a hunting strategy called persistence hunting. Instead of sprinting after prey in a short chase, they relied on endurance.

By maintaining a steady pace under the sun, they forced furry animals, overheated by their coats, to slow down and become easier to catch. You didn’t have to outrun a gazelle; you just had to outlast it. Sweating freely without a thick layer of fur made this possible.

Evolutionary Perspectives

Dr. Richard Wrangham, a biological anthropologist at Harvard University, highlights that hairlessness in humans may be linked to our evolutionary development as social animals. He suggests that reduced body hair allowed for better thermoregulation, especially as early humans migrated to hotter climates.

In his research, Wrangham states, 'A less hairy body would have helped our ancestors stay cool while hunting or gathering in the heat.' This adaptation provided a more effective means of survival, showcasing how evolutionary pressures shape physical traits over time, including our unique hair patterns.

Portrait of Petrus Gonsalvus and his wife Catherine, painted by Joris Hoefnagel around 1575.

To uncover the genetic basis for our relative baldness, my research team compared DNA from 62 mammals, including squirrels, armadillos, dogs, and humans. By lining up these genomes, we identified which genes remain active in furry species and which are muted or switched off in less hairy ones.

Humans didn’t lose the genes for growing hair—they’re still in our genome, just dialed down. In sporadic cases, these dormant hair-making genes can reactivate, leading to conditions like hypertrichosis—sometimes called “werewolf syndrome.”

People with hypertrichosis grow thick hair all over their bodies. One of the earliest recorded cases was Petrus Gonsalvus, born in Spain in the 1500s.

As a child, he was seen as curious in a cage at the French court. Eventually, King Henry II realized Petrus was just a regular person underneath all that hair. He received an education, married, and even inspired the fairy tale of “Beauty and the Beast.”

While hypertrichosis is exceptionally rare, it offers a glimpse into our genetic potential for hair growth. Our hair genes remain largely silent for the rest of us, with fine vellus hairs covering much of our skin and coarser terminal hairs only in specific areas.

National Gallery of Art.

This evolutionary shift, from a furry ancestor to a mostly hairless human, shows how trade-offs shape the path of life. In exchange for a fur coat’s insulation and protection, we gained the freedom to sweat, cool down efficiently, and thrive in hot climates.

That change helped our ancestors become endurance hunters and eventually migrate into diverse environments worldwide.

The absence of fur has interesting implications for human social behavior. Dr. Helen Fisher, a biological anthropologist and relationship expert, points out that less body hair may have enhanced social bonding. She explains that skin-to-skin contact is crucial for the release of oxytocin, the 'bonding hormone.'

Fisher states, 'As humans evolved, this lack of fur may have facilitated closer personal connections and cooperative behaviors, critical for survival in social groups.' To foster these connections today, experts recommend prioritizing tactile interactions, such as hugs or hand-holding, to enhance emotional bonding.

Therapeutic Insights & Recovery

Understanding why humans evolved to be less hairy involves a blend of biological, social, and environmental factors. As noted by evolutionary experts, this adaptation was not just about temperature regulation but also about fostering social connections. Dr. Richard Wrangham and Dr. Helen Fisher emphasize that these traits have shaped human interactions significantly.

Ultimately, by appreciating our unique evolutionary history, we can better understand the importance of social bonds and learn to cultivate deeper connections through simple actions like physical touch. This can enhance our relationships, promoting overall well-being.