Doug Bonderud

Nov 23rd 2020

Naked and Afraid? The Functional Fur Forfeit of Human Evolution


Why did humans lose their fur? It’s a hairy subject, one bristling with more questions than answers as scientists try to resolve the fuzzy picture of human evolution into something more clean shaven. It’s a strange shift: Why would our ancestors shed long locks in favor of naked bodies? And is this our final evolutionary iteration — or are we on track for completely hair-free forms?

Follicle Follies

Compared to most primates, humans are little more than pink, sweaty blobs of fat and water. Despite this follicular fallout, however, we remain obsessed with hair — many people will spend more than $100,000 in their lifetime having unwanted hair removed.

Part of the explanation for our depilation comes from an inhibitor protein known as Dickkopf 2 (Dkk2), according to Smithsonian Magazine. Recent rabbit research focused on plantar skin — the underside of the wrist in humans and the footpads in many other mammals — found both hair-covered plantar pads and a lack of Dkk2. And when mice with hairless plantar regions were given Dkk2-blocking mutations, they began sprouting fur.

As noted by Sarah Miller, dermatology professor at the University of Pennsylvania’s Perelman School of Medicine and co-senior author of the study, however, “Dkk2 is enough to prevent hair from growing, but not to get rid of all control mechanisms. There’s a lot more to look at.”

Occam’s Razor

While abundant Dkk2 delivery might help explain how humans became hairless, a bigger question remains: Why did humans lose their fur? As it turns out, explaining our denuded development is no easy task.

According to Scientific American, one popular theory is the “aquatic ape” — as protohumans began foraging in shallow lakes and rivers for food, fur both impeded their movement and made it hard to retain heat. As a result, we shed the fur and gained fat as protection. The problem? Fossil records for this aqua-loving ape are elusive, making it an outside contender for the fuzz-loss function.

Another option is the sweaty savanna suggestion; the notion that as humans moved out of forests and into the hot sun of savannas, hairy hominid bodies weren’t a great way to stay cool. As a result, we dropped the hair and gained sweat glands to offset the heat. Fire is the caveat here: Hairless bodies would keep us cool during the day but wouldn’t do the same at night — fire-building skills would have been essential to keep now-smooth bodies from freezing in the dark.

Other work suggests that parasite problems may have been the catalyst for our hair-free forms. Since hair offers an ideal habitat for everything from ticks and lice to flies — which could carry killer bacteria or viruses — clear skin made it easier for humans to stay healthy, along with increasing our ability to make and grip the tools needed to build fires and shelters. Holdover hair — often found on our heads and in pubic areas — remained to fill specific functions. Follicles on top helped protect human heads from overheating, while pubic proliferation may have continued to produce and deliver pheromones.

A Future Without Fuzz?

So what makes the cut in the next step of human evolution? Are we on track for entirely hairless bodies?

The answer may depend on feeling more than function. While it makes sense that climate change could conspire to reduce our follicle count, there’s only so far a hot Earth can take us before sweating won’t solve the problem; as a result, hair on our heads likely won’t disappear anytime soon. Work from evolutionary neurobiologist Mark Changizi, however, suggests that hair loss may have helped human communication by making it easier for us to recognize emotional and physical states. The theory is bolstered by the presence of three cones in human eyes — receptors that help see color — rather than two.

More cones means the ability to see greater ranges of color, something that wouldn’t be necessary for hunting fish or animals but would allow humans to better understand each other — so long as their heads were mostly hairless. From babies’ skin turning color if they’re sick or injured to the flush of anger, non-follicular faces may have empowered emotional communication.

Here, human-driven evolution, especially in the area of wearable and integrated technology, may pave the way for more follicle fallout. If devices do most of the talking for us, increased emotional attenuation may be advantageous for the continuing success of humankind at scale.

When it comes to the hairy question of why humans lost their fur, there’s no single answer: From aquatic apes to superior sweating, parasite protection and emotional empowerment, being fur-free is fraught with evolutionary potential.