Everything Everywhere Daily: History, Science, Geography & More - All About Hair

Starting point is 00:00:00 The following is an encore presentation of everything everywhere daily. If you are listening to me speak these words and can understand what I'm saying, then you are a human being. And if you're a human being, you're also a mammal. And if you're a mammal, you have hair, or at least the biological capability to produce hair. But why exactly do we have hair? What function does it serve? Why do we have less hair than other animals? And why do different people have different types of hair. Learn more about hair, what it does, and how it works on this episode of Everything Everywhere Daily. What if your perceptions about the past were wrong? ThruLine is a podcast that takes you back in time to uncover the parts of the story that may have gone unnoticed.

Starting point is 00:01:02 It effectively turned day into night and how it shaped the world now. Time travel with us every week on the ThruLine podcast from NPR. In this episode, I'm going to be talking about hair. However, I'm not just going to be talking about human hair. For all practical purposes, or at least for the purpose of this episode, hair, fur, and wool will all be the same thing. Fur is just hair on animals and wool is just animal fur that is turned into cloth. So let's start out with the obvious starting point for this discussion. What is hair? Hair is found only on mammals. It is a filament made of protein, primarily keratin.

Starting point is 00:01:51 Keratin is found on other animals and makes up scales, nails, feathers, horns, claws, and hooves. This is not to say that those things are the same as hair, but they all have a similar protein base. Hair generally consists of two parts. The shaft is what most people think of as hair. This is the long filament that is above the surface of the skin. The other part is the follicle. The follicle is located below the surface of the skin. This is the root of the hair strand and the part of the hair that is actually alive.

Starting point is 00:02:24 Hair fibers are predominantly made up of the cortex, which provides strength, color, and texture. The cuticle, a protective outer layer, and sometimes a medulla, which is a central core. This is a generalization because each species of mammal can have slight differences in hair and how hair strands are structured. For example, the quills on a porcupine are actually. actually hair, and hairs on a polar bear are very different than the hair on the mane of a lion. So the next big question is, what is the purpose of hair? Hair actually has several functions, the biggest of which is insulation and temperature regulation.

Starting point is 00:03:03 In colder environments, hair traps a layer of air close to the skin, reducing heat loss. Hair allowed mammals to exist in cold weather environments in which cold-blooded reptiles couldn't survive. Some mammals, such as camels, actually use their hair to keep cool. The temperatures of their fur can actually be significantly warmer than the temperature of their skin. The vast majority of mammals, but not all of them, are warm-blooded. One of the few mammals that aren't warm-blooded is the naked mole rat, and the naked mole rat has almost no hair. Being warm-blooded and having hair go hand-in-hand, but one thing we don't know is which came first.

Starting point is 00:03:44 Did hair allow for mammals to be warm-blooded, or did the fact that mammals were warm-blooded encouraged the evolution of hair? The reason we don't know the answer to this is because hair doesn't easily make fossils. In some environments, hair can decompose in just a matter of weeks. We can tell early mammals from their skeletal structure, but we can't tell when hair first appeared. The insulated value of hair is largely not a function of hair length. There are some mammals in the tropics with longer hair than some mammals. some mammals in the Arctic, but they have less insulation. Hair also has benefits beyond insulation

Starting point is 00:04:21 and thermal regulation. Hair can provide a layer of protection. It can protect the skin from ultraviolet rays, and in some species, hair can be thick enough to provide protection from physical damage. Hair can also serve as camouflage in mammals, and in some species, hair can serve as a sexual selection function similar to how birds use feathers. The next question you might have, and probably the most common question people have about hair, is why different people have different types of hair. There are roughly two different ways in which hair can vary between people, color and texture. Hair color comes from the presence of melanin in hair follicles and strands. There are only two types of melanin in hair that are responsible for all the various shades of hair

Starting point is 00:05:07 color, e-melonin and feel melanin. U-melon. U-melon is. is by far the most common form of melanin, and it comes in two forms, black e-melonin and brown e-melonin. Black hair is far and away the most common hair color in the world. Approximately 85% of the world's population has black hair. Another 11% of the world's population has brown hair. Collectively, black and brown e-melon is responsible for the hair coloring of about 96% of the world's population. Phyomelanin is much more rare.

Starting point is 00:05:44 Fio melanin is the melanin that is responsible for red hair. Only about 1% of the global population has red hair. However, there are many more people who actually carry the gene for red hair, and this includes people outside of Europe, including parts of North and West Africa. The genetic origins of red hair are believed to have come from Central Asia. The reason why so few people have red hair is because it's a recessive gene. That means that both parents have to carry the gene for someone to have red hair. And even then, if both parents carry genes for both e-melanin and feomelanin,

Starting point is 00:06:21 there is only a 25% chance that a child will have red hair. Blonde hair, and I should note that I'm talking about natural blonde hair, is only found in about 2% of the world's population. Blonde hair has either feomelanin or e-melanin, but it just doesn't have much of it. and blonde hair is basically defined by a relative lack of melanin. The rest of the population has some form of white or gray hair. White and gray hair is just hair with even less melanin than blonde hair or even a total lack of melanin.

Starting point is 00:06:56 While some small numbers of people have naturally white or gray hair, most people develop gray hair with age. Of course, these color classifications are not discreet. There are many shades of hair that can exist between black, brown, red, red, blonde, and gray. The other thing that varies between people is hair texture. Hair texture is generally classified into four different types, straight, wavy, curly, and kinky. Again, as with hair color, there's no bright lines between types of textures. Hair texture is separate from hair color. Someone can have straight black hair or curly black hair. However, like hair color, hair

Starting point is 00:07:37 texture is largely the result of genetics. The reason for hair texture has to do with the hair follicle. The shape of the hair follicle, whether it's round, oval, or twisted, and the angle at which the hair shaft grows out of the scalp influences whether or not hair is straight, wavy, curly, or kinky. Straight hair grows out of an almost perfectly round follicle, whereas curlier textures grow out of more oval or irregularly shaped follicles. These, these hair follicle differences result in changes to the hair strand. When the hair strand is created, it results in changes in the disulfide bonds between keratin strands. The more disulfide bonds and changes in the positioning of the bonds can result in tighter curls. As with hair color, it is entirely

Starting point is 00:08:26 possible for hair texture to change over someone's lifetime as well. Another question many people have about hair is, why are humans mostly hairless compared to other animals? This is more in the realm of speculation, but there are multiple theories as to why humans have less hair than other primates. One theory holds that the relative lack of hair on humans was due to humans evolving on the African savannah. Most apes live in forests where they are usually in the shade and where temperatures are cooler. When humans left the forest for grasslands, they encountered direct sunlight and higher temperatures, and this would have given evolutionary pressure to reduce the amount of hair so they could reduce body temperatures.

Starting point is 00:09:09 Another variation of this theory is that humans hunted on the savannah by engaging in long distance running. Almost any prey can outrun a human over a short distance. However, if you extend the distance, humans have the advantage. Larger animals, again covered in hair, will overheat over longer distances. The ability of humans to run farther without overheating would have been a huge advantage in hunting. Another theory is known as the aquatic ape hypothesis.

Starting point is 00:09:39 This somewhat controversial theory proposes that human ancestors went through a semi-aquatic stage, which led to adaptations such as bipedalism and the loss of body hair. Proponents suggest that, like other aquatic mammals, humans lost their body hair to streamline their bodies for swimming. However, this theory has less support among scientists due to a lack of direct fossil evidence of aquatic life stages in human evolution. Yet another theory posits that less hair may reduce the risk of harboring ectoparasites like ticks and lice, which can carry diseases. With less body hair, early humans could have a survival advantage by being less acceptable to diseases spread by these parasites.

Starting point is 00:10:20 A further theory is that humans evolved to have less hair through sexual selection. According to this theory, as human societies became more complex, traits seen as more attractive or desirable, such as less body hair, were selected for. and this could have been driven by a preference for visible skin as a display of health, or a preference for novel traits, which over generations led to reduced hairiness. Once humans migrated out of Africa and moved to colder climates, they were able to compensate for their lack of hair by wearing clothing and furs from other animals. As I mentioned before, hair and fur are really the same thing. However, while the basics of hair are generally the same,

Starting point is 00:11:01 many species have evolved very different types of hair. Polar bears have some of the most unique hair in the animal kingdom. Despite appearing white, polar bear hair is actually transparent. The hairs of a polar bear's coat are hollow, an unusual characteristic among mammals. This hollow structure provides excellent insulation, effectively trapping heat. And the air-filled shafts also help increase a bear's buoyancy while swimming. Another animal with unique hair are musk oxen. Musk oxen live above the Arctic Circle and have some of the best insulating fur in the animal kingdom.

Starting point is 00:11:40 Musk oxen have two layers of fur. During the winter they grow a very soft, short under layer of fur known as Kiviot. After the winter is over and spring begins, musk oxen shed their layer of Kiviot, and this is often collected by native Inuit people and turned into clothing. Kiviot is one of the highest quality. lightest, strongest, warmest, and most expensive wool products in the world. It is eight times warmer than regular sheep wool. I first encountered kiviot when I visited the Alaska Zoo, which had musk oxen. They would collect the kivet every spring and create a limited number of items like hats

Starting point is 00:12:18 and scarves. And they were some of the most expensive woolen items that I had ever seen in my life. A single ball of pure kiviot yarn sells for $150, and knitted products can sell for much, much more. Hats and scarves can go for several hundred dollars, and sweaters can sell for thousands. However, the winner of the warmest fur in the Animal Kingdom contest goes to the sea otter. Unlike most aquatic mammals, sea otters do not rely on a layer of body fat for insulation. They rely almost entirely on their hair to keep them warm. Sea otter fur is the most dense fur of any mammal in the world. They have 150,000 strands of hair per square centimeter, or 970,000 strands per square inch.

Starting point is 00:13:12 The combination of longer guard hairs and short underfur hairs keeps water off of the sea otter skin, keeping it warm. The thickness of sea otter fur made it a target for fur traders and caused their population numbers to decline rapidly in the 19th century. All of us deal with hair almost every day, but most people don't think about how complicated or how important hair is. Hair is one of the things that makes mammals what they are and what helps give most of us a unique identity. The executive producer of Everything Everywhere Daily is Charles Daniel.

Starting point is 00:13:51 The associate producers are Austin Oakden and Cameron Kiefer. I want to thank everyone who supports the show over on Patreon. Your support helps make this podcast possible. I'd also like to thank all the members of the Everything Everywhere community who are active on the Facebook group and the Discord server. If you'd like to join in the discussion, there are links to both in the show notes. And as always, if you leave a review or send me a boostagram, you two can have it read on the show.

Everything Everywhere Daily: History, Science, Geography & More - All About Hair

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