Hair

A Human History

Kurt Stenn

• Publisher: Pegasus Books
• Year: 2016
• Print ISBN: 9781681773469
• eBook ISBN: 9781681771021
• Topic: History
• Subtopic: Social History
• Index: History

A microhistory in the vein of Salt and Cod exploring the biological, evolutionary, and cultural history of one of the world's most fascinating fibers. Most people don't give a second thought to the stuff on their head, but in Hair, Kurt Stenn — one of the world's foremost hair follicle experts — takes readers on a global journey through history, from fur merchant associations and sheep farms to medical clinics and patient support groups, to show the remarkable impact hair has had on human life.From a completely bald beauty queen with alopecia to the famed hair-hang circus act, Stenn weaves the history of hair through a variety of captivating examples, with sources varying from renaissance merchants' diaries to interviews with wig makers, modern barbers, and more. In addition to expelling the biological basis and the evolutionary history of hair, the fiber is put into context: hair in history (as tied to textile mills and merchant associations), hair as a construct for cultural and self-identity, hair in the arts (as the material for artist's brushes and musical instruments), hair as commodity (used for everything from the inner lining of tennis balls to an absorbent to clean up oil spills), and hair as evidence in criminology.Perfect for fans of Mark Kurlansky, Hair is a compelling read based solidly in historical and scientific research that will delight any reader who wants to know more about the world around them.

1

THE FIRST FIBERS

The first hairs arose in a reptilelike, mammalian ancestor.

All biological forms at any level—whether societal, cellular, or organismal—must separate themselves from the outside in order to survive: Each must have a wall. At the societal level, that wall shields a kingdom from its enemies. At the cellular level, the membrane, another type of wall, surrounds, defines, and contains the cell nucleus and cytoplasm. At the organismal level—be it frog, chicken, or monkey—that wall is skin. Our story must therefore start with mammalian skin, not only because hair grows out of skin, but also because hair enhances the wall-like properties of skin by buffering it from trauma, protecting it from temperature extremes, and sensing the environment before actual contact.

All organs, like the hair shaft (the hair fiber) and its follicle (the hair root that gives rise to the fiber), are made of three different cell types. The first is a bachelor cell, which tends to live alone without making long-lasting relationships with other cells. These cells wander about the body, mostly within vessels as blood cells, carrying freight or messages, but always traveling and functioning alone. Eggs and sperm are examples of such cells, and they remain single for a long time; in fact, their job—finding a partner—could not be consummated if they were dragging along one or several petulant little brother or sister cells.

The second type is a cell that manufactures cell matrix, the soupy or solid materials that surround cells. By means of the matrix, such cells provide the undergirding for all body tissues and organs; they generate collagen, elastin, bone, and cartilage. Relevant to skin, these cells give rise to a collagen-rich layer of the deep skin called dermis.

The third type of cell makes up epithelium. These cells characteristically bind tightly to one another. They are highly social beings; if separated, they become fidgety, seeking to link up to one or more neighbors. As they stick firmly to one another, they make up a good cover for any biological plane, such as the surface layer of the heart or lung or the outmost layer of the skin. At the same time, they form the core of many three-dimensional organs, such as the salivary gland, liver, and kidney. Because epithelial tissues are made essentially of cells alone, they are, in general, soft and need outer structural support, such as bone, cartilage, and collagen. Thus, when epithelial cells form a sheet, such as the epidermal covering of the skin, they need a supportive underlying layer: the dermis.

The mammalian skin surface, then, is made of a multilayered epithelium, the epidermis, which lies over a thick, leathery tissue, the dermis. Infiltrating the dermis are cells, nerves, and vessels, which nourish the skin. The hair fiber coming out of the skin arises in a hair follicle, a fingerlike down-growth of the epidermis. In humans, the first hair follicle forms in the fetus as a bud at the base of the primitive epidermis. This bud projects down into the dermis as an extension of the epidermis and is nurtured and supported by the dermis.

The completely mature hair follicle consists of epithelial cell layers except for a small collagenous nubbin within its base called the dermal papilla. The epithelial layers of the follicle look like a collapsible telescope with three sleeves. The innermost sleeve is solid and forms the hair shaft, the outmost sleeve serves as a cellular wall separating the hair follicle from the dermis, and the middle layer holds and molds the shaft on its way out. Growing off the central hair follicle is a muscle, which pulls the follicle and its shaft upward after a fright or a chill, and a sebaceous (or oil) gland, which squirts greasy liquid onto the surface of the hair shaft as it grows out.

Except for the palms, soles, and some special regions (such as the lips, anus, and glans penis), hair is present on all skin surfaces. Nevertheless, humans have been referred to as the “naked ape” because, unlike other mammals, most human skin is covered by short, thin, lightly pigmented, and soft hairs—like the hair on your forehead, barely noticeable.

So if that’s what hair is, the next question is this: Why did we and other mammals acquire hair in the first place? From where did it arise and how has it helped humans become sapiens?

The origin of hair is based on the evolution of animal life.

Life itself appeared on earth about three and a half billion years ago, surprisingly soon after the formation of the planet, a billion years earlier. The first life-forms were unicellular—simple, single, and independent. The next evolutionary step, which took two billion years, involved the formation of soft and jellylike multicellular organisms; these could survive and flourish anywhere as long as they were floating in water. For them to leave a liquid environment and move onto land, however, they had to acquire a supporting structure of some sort: Either the cells on the outside had to harden or the cells on the inside had to provide a framework. The former became an exoskeleton, a surface armor, which is seen in house flies, crayfish, and snails; the latter became an internal framework, a skeleton with a segmented backbone, as seen in tree frogs, rattlesnakes, wombats, and humans. The earliest backbones, or vertebrae, appeared in primitive fish about five hundred million years ago. It would require another one hundred million years before the vertebrates took a deep breath and made that fateful evolutionary step out of the oceans and onto dry land.

With the appearance of the vertebrates, a dramatic change occurred in the structure of skin: The outer epithelial layer transformed from a single layer of cells to a multilayer of cells. This was a pivotal event for our topic because the hair shaft and the hair follicle consist of packed cells that could only have derived from a multilayered structure. While the lobster, an invertebrate, has other redeeming features, there is no way he or his cousins the locusts (or their distant relatives, the earthworms) could make a hair shaft because their surface epithelium is single-layered. The invertebrates are able to augment their skin surface with noncellular materials, such as mucus (in the case of slugs), shells (for periwinkle) or chitinous materials (for beetle skin), but they do not have the wherewithal to produce a tissue of piled up, tightly adherent, epithelial cells like we vertebrates do.

If we extend our family lineage back about three hundred million years, we would be hard pressed to recognize any family resemblance to the vertebrates existing at the time. However, the morphological and molecular records are clear: We mammals share an ancestor with the reptiles, an as-yet unknown creature called a “stem reptile.” The relationship is driven home by the example of the duck-billed platypus, which is classified as a primitive mammal. This semi-aquatic denizen of eastern Australia lays eggs, suckles its babies with a form of milk, and grows hair. In terms of classification, the platypus is a contradiction: mammals have hair, make milk, but don’t lay eggs; they birth live young. It’s very revealing that some of the platypus genes are common to mammals, others to birds, and yet others to reptiles. This animal represents one very early point in the evolutionary crossroad. Its genome reflects the traits making up the first, most primitive mammals, as well as what remains from our reptilian predecessor, whose descendants sired all the great landed vertebrates: the reptiles, dinosaurs, birds, and mammals.¹

Our skin and its appendages reflect at least to some extent what this ur-forebear bestowed on us. When animals left the primordial seas for land, their skin had to protect them from a wholly new, not always friendly environment: dry air, electromagnetic radiation (strong light), oxygen toxicity, physical trauma, and extreme temperature fluctuations. This necessitated dramatic changes in the epidermis; it acquired thickness, strength, and water barrier properties. With time, discrete regions of the epidermis projected upward and folded down upon themselves, thereby amplifying their protective properties. In fish and reptiles, these raised portions formed flat and broad-shaped scales. In birds and mammals, they formed pointed growths—filaments that extended beyond the skin surface. For birds, that filament branched and evolved into a feather; for mammals, that filament remained threadlike: a hair.

Over the years, ideas concerning the origin of hair have varied widely. One current school proposes that hair evolved from the stem reptile’s scales, a notion suggested by the fact that there are small hairs sitting in the hinge region of the scaly tail-skin of most rodents. A second hypothesis suggests that the shaft arose within a gland and initially served a role directing oily secretions from the gland onto the skin surface. This idea is based on the observation that all follicles have oil glands, that the cuticle layer of the hair shaft is structured to scoop oils to the skin surface, and that the earliest animals needed oil on their skin to prevent water loss. A third theory, which is not exclusive of the first two, considers that hair arose from hairlike sensory structures seen on the skin of some living fish and amphibians. These structures serve to alert the fish of an environmental danger, such as the water pulse of an approaching predator or the presence of an adjacent sharp rock.

In fact, there’s a lot of evidence that the hair follicle and its shaft play important sensory roles. Studies in mice suggest that each hair type has its own distinct sensory system so that different hairs provide different types of sensation. While all hairs are invested with nerves and thus capable of perceiving movement, there are large and uniquely sensitive hairs found on the upper lip of most mammals. These whiskers are so important to mouse sensation that they have been elevated to the status of a “sensory organ”; in fact, they have inherent erectile properties, which, when stimulated, draw the prominent shafts to attention. For a mouse probing the world at night, its whiskers serve as valuable antennae reconnoitering the terrain well before a tender nose arrives.

Hair is an important sensory device for humans as well. In a common life experience, small hairs on the outstretched arm accurately perceive a close-passing person or a zephyr riding in with the tide on a warm summer day. People are also able to detect bedbugs more efficiently on an unshaven arm than a shaved one.²

In recent years, we have learned that in addition to its rich supply of nerves, the hair follicle is surrounded by dermal cells, which, under the proper conditions, can act like nerves. These cells contain proteins also found in nerve cells, and when they are isolated and grown in tissue culture, they can become neural. In fact, when Dr. Robert Hoffman and his research team transplanted these cells into a paralyzed rat, the cells not only supported nerve repair but they also integrated into newly formed nerves that allowed the rat to recover function.³

Hair also plays a role in temperature control. A turtle on a log, with up-stretched head catching the early morning sun, reminds us that reptiles do not have an internal means of generating heat. From its cool and protected bower in a deep stream, the turtle awakes from its slumber, moseys onto a floating log, and into a beam of strong morning sun; there he basks. Like all cold-blooded animals, he depends on nature’s primary radiant energy source, the sun, to get started. But the smooth-surfaced skin that allows him to readily take up heat from his surroundings during the day also causes him to lose it to his surroundings during the night. That his body temperature drops during the night is to his advantage, because during these times he doesn’t need high-priced fuel (i.e., hard-earned foodstuffs) to keep warm. The trade-off for his caloric frugality, though, is his nocturnal and early morning languor.

In contrast to reptiles, the earliest mammals could hunt in the cool night and early morning because of two major advantages over their cold-blooded neighbors. The first was that they were able to generate heat by metabolic processes without direct help from the sun.⁴ The second was that, over eons, their primitive skin sensory filaments had increased in density to form a skin cover that served as a highly efficient insulator: a fur coat. These two features—warm-bloodedness and insulation—enabled them to forage among the nests of their ectothermic neighbors at night and hide from them during the day.⁵

Heat flows from a warmer to a cooler body, as anyone who has ever jogged on a blistering cold day knows, warming in open sunny spots and then cooling again in the shade. In this case, solar heat transmits over space directly to us, as it does to the basking turtle. But heat can also transfer from body to body by direct contact. When you burn yourself eating a straight-out-of-the-oven pizza, for example, you are experiencing the direct spread of heat from the body of the pizza to the body of your mouth. Heat can also transfer by means of moving currents of water or air, a process referred to as convection. For instance, heat transfers by convection when air blowing from a hair dryer picks up heat from the heat filament and transfers it to your locks.

In all these examples, heat transfers from a warmer body to our body. But heat can flow in the opposite direction as well, from our warm body to the cold outside. The Coney Island Polar Bear Club stalwarts celebrate New Year’s Day by warming up the frigid waters of the Atlantic Ocean. Moving heat in that direction might be fun for a short while, but after a not-too-long exposure to such cold, about ten to twenty minutes, vital functions not only slow, they stop.⁶

Active mammalian life depends on a constant body temperature of around 98.6ºF, and skin plays an active role in maintaining it. While skin is not important for heating up the mammalian body, it is very important for minimizing heat loss—and this is where hair comes in. Fur efficiently blocks all forms of heat transfer. It does this, first of all, because it grows as a dense array of hairs. Beaver skin, for example, has around forty thousand shafts in an area of skin about the size of a fingertip. At this density, fur is virtually an impenetrable barrier; neither wind, water, nor insects can get through. In addition, hair itself is a poor thermal conductor—eight thousand times less conductive than copper.⁷ Dense hair cover also traps air, and air is an even poorer conductor of heat than hair. As long as hair holds a layer of air over the skin and prevents it from moving (convection), no heat is lost. Heat cannot transfer through the fur barrier either from the skin surface to the outside or from the outside to the skin surface. Fur surface mirrors environmental temperatures, and skin surface, under the fur coat, mirrors body core temperature. In an effort to expand that cosseting layer of air and thus enhance the insulating properties of furred skin, hair follicle muscles pull the shafts upward when an animal becomes chilled. This action increases the thickness of the fur coat and the efficacy of the insulation in all animals—except humans, of course, because we have lost our “fur.” So when humans chill, although our hairs stand up, giving us “goose flesh,” this ancient reflex is really just bluffing, because our body hairs are neither big enough nor dense enough to maintain the important stationary and insulating air layer.

Befitting its reputation as the fastest land animal, the cheetah can attain speeds as high as seventy-one miles per hour, but can only hold that speed for less than a minute before its body temperature rises and forces it to stop and cool off. This is not to belittle the skills of the cheetah, but rather to point out that fur limits its endurance in the unrelenting heat of tropical Africa. Because of fur, the cheetah has only a few means of dissipating body heat: stop running, get into the shade, start panting, lick its paws, or expose its non–fur covered body parts (primarily the paws and ears) to the surrounding air. If the savannah is as hot as or hotter than the cheetah, it will be hard pressed to cool itself at all, as heat flows to the cooler body. Thus, in this climate, mammalian adaptive success is paradoxically limited by the heat-retaining properties of fur, because fur prevents body heat from dissipating through it by any heat-transfer mechanism. Such an efficient cover would have prevented the evolution of man.⁸

Scientists have calculated that on a hot and sunny day, fur-covered, upright hominids would have suffered a heat stroke after about ten to twenty minutes of a nonstop walk; they just couldn’t dissipate heat from their bodies quickly enough.⁹ Our human antecedents needed to move around during the day in order to hunt and survive, yet they had to keep their body temperature at 98.6ºF, so they needed a better cooling-off mechanism. The problem was complicated by the fact that the human’s efficient evolution was dependent on a huge brain (the largest brain-to-body-size ratio of all animals, in fact) and yet brain tissue is exquisitely sensitive to elevated body temperatures: Heat stroke occurs at 104ºF and brain death at 107ºF. In addition, brain tissue temperature is regulated by core body temperature and the only way any animal, including a human, can shed excess body core heat is by way of the skin. For an evolving hominid, the dense hair cover had to go.¹⁰

Many ideas have been put forth to explain the loss of hominid body hair. One fanciful notion suggested by Charles Darwin contended that prim...

Table of contents

• Cover
• Title
• Contents
• Foreword: Telling the Story of Hair
• Part One: Shaping the Shaft
• Part Two: The Ultimate Communicator
• Part Three: In Human Service
• Epilogue: A Glimpse of the Future
• Illustrations
• Acknowledgments
• Glossary
• Selected Bibliography
• Notes
• Index
• Copyright