When you think about hairless mammals, there are really only a few that come to mind. You have the naked mole rat, a name that is incredibly apt when you look at one of them. The Sphynx, the Xoloitzcuintle, and the Peruvian Inca Orchid are all hairless, but we let these cute cats and dogs into our homes. And perhaps the one that looks most like a person – -at least in terms of there clearly being hair, but not everywhere – is the Chinese Crested dog breed.
Most of these animals don’t have hair because of genetic mutations or issues that caused them to not have hair. The naked mole rat is an example of an animal that evolved to get rid of the obvious thick fur that most rodents – and land mammals – have.
That is exactly what happened to our own hair. Though it is hard to tell, naked mole rats are not hairless, just like the human body isn’t hairless.
With two very distinct histories, we know that the reason the naked mole rat has evolved to have far less hair is not the same reason why humans have so little obvious hair.
How and Why Did Humans Lose Our Fur?
Keeping in mind that a lot of this is speculation based on the modern human body, let’s take a look at what many think caused humans to lose that fuzzy look.
Is Hair Different from Fur?
It’s probably best to get this out of the way now. The truth is that hair and fur really aren’t different. The hair you have is the same as what a dog or porcupine has. They have the same composition and are made of keratin. When you think about humans, dogs, and porcupines, it’s easy to see what makes people think that there is a difference in how the hair is used.
Porcupines have evolved so that their hair creates spikes – kind of similar to video game characters in the 1990s. For them, hair is a weapon to protect themselves.
Dogs have hair that is much more common in mammals, and it is a lot more like our own. At least our easily visible hair. Most mammals have similar hair (not the specialized type of a few very species), and it serves a similar function.
The question is why aren’t humans covered in hair?
The most likely hypothesis – Persistence Hunting
The problem with trying to understand when humans probably started evolving to have increasingly less hair isn’t something that anyone can state with certainty. Like most of the rest of your body, once you die, your hair will decompose. All we have left of humans from millennia ago is their bones.
It is incredibly difficult to pinpoint when it happened, but there are a lot of signs that indicate why it happened.
Humans don’t have the same kinds of natural advantages that most animals have. We don’t have claws or particularly sharp teeth. We aren’t very big, and we aren’t nearly as agile or as fast as many other animals.
This does seem to set us at a significant disadvantage. But what humans do have is the ability to be persistent hunters. We are the only animals that are able to hunt for hours at a time, basically running our prey to exhaustion and death.
Walking upright is a large part of why early humans could hunt for long periods of time – something that most of us probably can’t achieve today. Researchers think that humans started to lose their hair when we became persistent hunters. The less hair early humans had, the easier it was to stay cool during the heat of the day and when they were out in the sun. We still retain the same benefits from the loss of hair.
That’s right. Your lack of a fuzzy physique is almost certainly a result of needing to stay cool so that your ancestors could hunt for long periods of time.
The other theories
There are some researchers who think that the evolution to having increasingly less hair is a result of people preferring partners with less hair. While this is almost certainly a reason why people prefer a partner today, this wasn’t exactly likely when we were all roughly as furry as apes. When survival is far less certain, the factors that make a partner more desirable tend to focus on skill over a trait that is more superficial. If an early human was looking at the physical appearance of a potential mate, they would be more interested in muscle and agility. These factors would indicate a better partner to increase the chance of survival.
Other researchers have posited that humans evolved to have less hair to reduce parasites, like fleas and lice, on their bodies. Again, this isn’t really something that is likely to play a significant role in a species losing their hair. If it were, far more animals would have gone the same route. Grooming was also a way of bonding for early humans and some animals. Parents still groom their children’s hair, creating a similar type of bonding experience.
Both of these theories are more likely to be about the preferences or benefits that came as a result of the hair loss, not a cause for it.
Before we talk about the next possible reason, it’s important to understand how the cooling mechanism works in mammals.
How mammals cool down
The process of cooling down is called thermoregulation. For most mammals, this is done through panting, unless the animal can stick to the shade or is close to a source of cool water. You do have some animals that have their own unique methods, like elephants. They have large ears that they can fan to help get rid of some of the heat because the big ears increase their surface space.
Humans are fairly unique because we rely on our sweat glands. Dogs and cats actually do have some ability to sweat through sweat glands located on their paws, but it isn’t particularly efficient. Other animals that sweat more like humans include apes, monkeys, horses, hippos, and pigs.
Two of those animals probably stick out because they do seem a lot more similar to humans – hippos and pigs. When you look at pictures of them, they don’t look nearly as hairy as a lot of other animals. Also, like humans, they do still have a lot of hair, it is just far shorter and lighter than the hair that most mammals have.
Perhaps the animal species that has a more similar need for sweat glands is the horse. Considering how much horses run, they really need to be able to sweat to cool down. Still, they have a lot more obvious hair than we do. Ironically, they also have much more obvious masses of hair in their manes and their tails.
Why a need to sweat likely led to the loss of hair
This theory about hair loss is actually pretty easy to figure out without a lot of thinking. If you have long hair, you know exactly how hard it is to cool off when your hair isn’t tied back and out of the way. Wherever it touches, it tends to get in the way, blocking your ability to cool down. You toss it out of the way, it comes slapping back to another part of your body, increasing your frustration and stress.
Imagine if you had a lot more hair – everywhere on your body. Your arms have a coat of hair that is a couple of inches long. Your legs are covered in the stuff. Even your body is absolutely coated in it. You don’t need clothing to stay warm because you have hair that can do a fantastic job of keeping your temperature from fluctuating over a short period of time.
Sweat glands release sweat, which helps to cool the skin down fairly quickly. With less hair, this process is much more efficient. The cooler early humans could be while hunting an animal, the longer they could continue to hunt. As a result, humans were able to finally have a significant advantage in terms of hunting.
Early humans no longer had to be faster than any other species or stronger than them. They were able to wait the animals out because eventually the animals would run out of stamina, making them entirely vulnerable to the hunters.
The hair didn’t go away, it just got smaller and lighter. Except in a few obvious places.
The hair we still have
As difficult as it is to imagine, we actually have roughly the same amount of hair as chimps. We do have fewer hair follicles than most of our fellow primates. Hair follicles are located under the skin and they are little sacs where the hairs form and grow.
What really stands out though is just how tiny most of our hair is compared to the hair on most mammals. There are only a few areas of the human body where hair is far more obvious when you are standing a few feet away from other humans. The closer you get, the easier it is to see that humans are actually still covered in hair, it’s just not nearly so obvious.
This is where attraction likely has helped to keep some hair much thicker and more obvious.
The most obvious hair is on the top of most people’s heads. The hair on top is considered a trait that is attractive today, and people can take up a lot of time styling their hair to improve their appearance. However, it also has practical uses. Remember that long hair from earlier – when it was getting in the way of sweating? It can be very useful when it gets cold. Although it doesn’t work nearly as well as a coat of fur, it does help to retain some heat.
Your head has a lot more hair than just what’s on top. Men have much more obvious facial hair, but it doesn’t have an apparent purpose beyond making it obvious what a person’s gender is. The eyebrows and eye lashes are also a type of hair that you would very much miss if they weren’t there. They obviously play a part in what is considered a beautiful or not so beautiful appearance, but they also have a very important function in protecting your eyes. Eyebrows have another purpose – they are part of facial expressions and how we communicate.
The next most obvious hair is around the genitals and armpits. Why these areas remain so hairy is largely a guess, with many researchers thinking it probably has to do with identifying gender. The hairs in these regions help to enhance the smell of a person. People can identify each other by the natural scent, so there may be something to that.
Finally, there are the little hairs that are actually everywhere else. Your arms and legs obviously have hair, but so does your neck, your cheeks – both on your face and backside – even in your ears. These small hairs are called vellus hair, but are more commonly known as peach fuzz. It is primarily a way of protecting your skin from the elements. In fact, the only places that do not have hair are your palms and the bottoms of your feet. Pretty much everywhere else is covered, just not in a way that is nearly so obvious.