Hair
Encyclopedia
Hair is a filament
ous biomaterial
, that grows from follicles
found in the dermis
. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class
.
The human body, apart from its glabrous skin, is covered in follicles which produce thick terminal
and fine vellus hair. Most common interest in hair is focused on hair growth, hair types and hair care
, but hair is also an important biomaterial
primarily composed of protein, notably keratin
.
The word "hair" often refers to two distinct structures:
Hair fibers have a structure consisting of several layers. Starting from the outside:
Each strand of hair is made up of the medulla
, cortex
, and cuticle
. The innermost region, the medulla, is not always present and is an open, unstructured region. The highly structured and organized cortex, or middle layer of the hair, is the primary source of mechanical strength and water uptake. The cortex contains melanin
, which colors the fiber based on the number, distribution and types of melanin granules. The shape of the follicle determines the shape of the cortex, and the shape of the fiber is related to how straight or curly the hair is. Asian hair typically has a round fiber and is quite straight. Oval and irregularly-shaped fibers are generally more wavy or even curly. The cuticle is the outer covering. Its complex structure slides as the hair swells and is covered with a single molecular layer of lipid that makes the hair repel water. The diameter of human hair varies from 17 um.
Hair growth begins inside the hair follicle
. The only "living" portion of the hair is found in the follicle. The hair that is visible is the hair shaft, which exhibits no biochemical activity and is considered "dead". The base of the root is called the bulb, which contains the cells that produce the hair shaft. Other structures of the hair follicle include the oil producing sebaceous gland
which lubricates the hair and the erector pili muscles, which are responsible for causing hairs to stand up. In humans, with little body hair, the effect results in goose bumps
.
Hair follows a specific growth cycle with three distinct and concurrent phases: anagen, catagen, and telogen phases. Each has specific characteristics that determine the length of the hair. All three occur simultaneously; one strand of hair may be in the anagen phase, while another is in the telogen phase.
The body has different types of hair, including vellus hair and androgenic hair
, each with its own type of cellular construction. The different construction gives the hair unique characteristics, serving specific purposes, mainly warmth and protection.
and other hairs that serve different functions. Hair provides thermal regulation and camouflage
for many animals; for others it provides signals to other animals such as warnings, mating, or other communicative displays; and for some animals hair provides defensive functions and, rarely, even offensive protection. Hair also has a sensory function, extending the sense of touch beyond the surface of the skin. Guard hairs give warnings that may trigger a recoiling reaction.
and cooling (when sweat evaporates from soaked hair) as well as protection from ultra-violet radiation exposure. The function of hair in other locations is debated. Hats and coats are still required while doing outdoor activities in cold weather to prevent frostbite
and hypothermia
, but the hair on the human body does help to keep the internal temperature regulated. When the body is too cold, the arrector pili muscles found attached to hair follicles stand up, causing the hair in these follicles to do the same. These hairs then form a heat-trapping layer above the epidermis
. This process is formally called piloerection, derived from the Latin words 'pilus' ('hair') and 'erectio' ('stiffening'), but is more commonly known as 'having goose bumps
' in humans. This is more effective in other mammals whose fur fluffs up to create air pockets between hairs that insulate the body from the cold. The opposite actions occur when the body is too warm; The arrector muscles make the hair lay flat on the skin which allows heat to leave.
, but much of the hair on the human body is suited to protect it. This natural armor cannot directly protect humans from potential predators, but it does help to keep the sense organs, such as the eyes, working properly.
s provide some protection to the eyes from dirt
, sweat
, and rain
. More importantly, they play a key role in non-verbal communication
. In many other mammals they contain much longer, whisker-like hairs that act as tactile sensors.
The eyelash
grows at the edges of the eyelid and protects the eye from dirt. The eyelash
is to humans, camels, horses, ostriches etc., what whiskers are to cats; they are used to sense when dirt, dust
, or any other potentially harmful object is too close to the eye. The eye reflexively closes as a result of this sensation.
traced the origins of hair to the common ancestor of mammals, birds, and lizards that lived 310 million years ago. The study found chickens, lizards, and humans all possessed a similar set of genes that was involved in the production of alpha keratin
. In chickens and lizards, the α-keratin produced was found in their claws, but in mammals it was used to produce hair. The scientists involved continued searching for the mechanisms that allowed mammals to use the keratins of animal claws to produce hair.
Humans are the only primate species that have undergone significant hair loss and of the approximately 5000 extant species of mammal, only a handful are effectively hairless. This list includes elephants, rhinoceroses, hippopotamuses, walruses, pigs, whales and naked mole rats . Most mammals have light skin that is covered by fur, and biologists believe that early human ancestors started out this way also. Dark skin probably evolved after humans lost their body fur, because the naked skin was vulnerable to the strong UV radiation as would be experienced in Africa. Therefore, evidence of when human skin darkened has been used to date the loss of human body hair, assuming that the dark skin was needed after the fur was gone.
Dr. Alan R. Rogers, an evolutionary geneticist at the University of Utah, used mutations in the MC1R gene to estimate when human skin darkened. He said early humans may have gone through several genetic "clean sweeps" with light-skinned individuals dying off and dark-skinned individuals surviving. He estimates the last of these clean sweeps took place 1.2 million years ago. Therefore, apparent bareness in humans, likely has existed at least since that time. Later when humans began to live in more northerly latitudes, however, light skin became an advantage for the production of vitamin D
and the recessive gene began to become more prevalent in those populations.
Balding
, where terminal hair
switches to vellus hair, usually occurs at around thirty to forty years of age. In prehistoric times, most individuals were not as likely to live past 30, with few reaching their fourth decade, and thus it wasn't likely that this trait was subject to selection.
Most species evolved as the climate in Africa changed, to adjust their thermoregulation
to the intense UV and sunlight at the equator, mostly by panting. Early hominids likely possessed fur similar to other large apes, but about 2.5 million years ago they developed a greater distribution of sweat glands that enabled them to perspire over most of the body. It is not clear whether the change in body hair appearance occurred before or after the development of sweat glands. Humans have eccrine sweat glands
all over their bodies. Aside from the mammary glands that produce a specialized sweat called milk
, most mammals just have apocrine sweat glands
on their armpits and loin. The rest of their body is covered in eccrine glands. There is a trend in primates to have increased eccrine sweat glands over the general surface of the body. It is unclear to what degree other primates sweat in response to heat, however.
The sweat glands in humans could have evolved to spread from the hands and feet as the body hair changed, or the hair change could have occurred to facilitate sweating. Horses and humans are two of the few animals capable of sweating on most of their body, yet horses are larger and still have fully developed fur. In humans, the skin hairs lie flat in hot conditions, as the erector pili muscles relax, preventing heat from being trapped by a layer of still air between the hairs, and increasing heat loss by convection.
Historically, some ideas have been advanced to explain the apparent hairlessness of humans, as compared to other species.
The thermoregulatory hypothesis (first proposed by Darwin in 1871 and later developed by Dr. Peter Wheeler, 1984, 1985) suggests that a need for decreased body hair originated as a response to climate change that began approximately 3 million years ago . At this time, the earth entered a period of global cooling that had a dehumidifying effect on the main early human habitats in East and Central Africa. Lush, wooded forests gave way to dry, grassland savannah; because of this, early humans were required to travel farther in search of food and water. As early humans diverged from their chimpanzee-lineage, they also became omnivorous in order to maximize calorie intake, an important distinction in a nutrient-scarce environment. Prey, however, are moving targets, and though early humans changed the traditionally ape-like appearance of the australopithecines and adapted long, strong legs to facilitate sustained running, dense, hairy coats still posed a potentially fatal risk of causing overheating during the chase . It is posited that thick hair got in the way of the sweat evaporating, so humans evolved a sparser coat of fur. Although hair provides protection against harmful UV radiation, since our hominin ancestors were bipedal, only our heads were exposed to the noonday sun. Humans kept the hair on our head which reflects harmful UV rays, but our body hair was reduced. The rise in eccrine glands occurred on the genes that determine the fate of epidermal stem cells in human embryonic development. Opponents of the thermoregulatory hypothesis would say that losing hair added an extreme weakness to cold, but, seeing as how humans figured out cutlery around 2.6 million years ago, our ancestors easily could have found clothing within the 1.4 million years between cutting up their kills and losing their hair.
The aquatic ape hypothesis
posits that sparsity of hair is an adaptation to a semi-aquatic environment, but the theory has yet to gain support among scientists.
Another hypothesis for the thick body hair on humans proposes that Fisherian runaway
sexual selection
played a role (as well as in the selection of long head hair), (see types of hair and vellus hair), as well as a much larger role of testosterone in men. Sexual selection is the only theory thus far that explains the sexual dimorphism
seen in the hair patterns of men and women. On average, men have more body hair
than women. Males have more terminal hair
, especially on the face
, chest
, abdomen
, and back, and females have more vellus hair, which is less visible. The halting of hair development at a juvenile stage, vellus hair, would also be consistent with the neoteny
evident in humans, especially in females, and thus they could have occurred at the same time.. This theory, however, has significant holdings in today's cultural norms. There is no evidence that sexual selection would proceed to such a drastic extent over a million years ago when a full, lush coat of hair would most likely indicate health and would therefore be more likely to be selected for, not against.
A final hypothesis is that human hair was reduced in response to ectoparasites. The “ectoparasite” explanation of modern human nakedness is based on the principle that a hairless primate would harbor fewer parasites. When our ancestors adopted group-dwelling social arrangements roughly 1.8 mya, ectoparasite loads increased dramatically. Early humans became the only one of the 193 primate species to have flees, which can be attributed to the close living arrangements of large groups of individuals. While primate species have communal sleeping arrangements, these groups are always on the move and thus are less likely to harbor ectoparasites. Because of this, selection pressure for early humans would favor decreasing body hair because those with thick coats would have more lethal-disease-carrying ectoparasites and would thereby have lower fitness. Additional evidence for this hypothesis comes from studies that show that most ectoparasites on modern humans are confined to the head and pubic regions. Early humans were able to compensate for the loss of warmth and protection provided by body hair with subcutaneous fat and clothing. Hairlessness could maintained in modern society by sexual selection for hairless partners in addition to natural selection to reduce parasite loads.
approximately 2.5 million years ago. They devised new hunting techniques. The higher protein diet led to the evolution of larger body and brain sizes. Jablonski postulates that increasing body size, in conjunction with intensified hunting during the day at the equator, gave rise to a greater need to rapidly expel heat. As a result, humans evolved the ability to sweat: a process which was facilitated by the loss of body hair. A major problem with this theory, however, is that it does not explain why males are larger, hairier, and were more active in hunting than females. The female-male size differential among other closely associated primates is much greater than among humans, however, so it might have been reduced during evolution.
Other primates have sweat gland in their armpits that function as those of humans, and thus it is probable that human sweat glands evolved from a similar distribution, spreading to more areas of the body, rather than occurring through evolution of a new trait. It is not known whether the increased distribution of sweat glands occurred before, during, or after, the change in body hair, or even whether the two are related developments. Horses also sweat, and they are larger, hairier, and expend more energy running than human males, so there may not be any connection between the ability to sweat and the apparent hairlessness of humans.
Another factor in human evolution that also occurred in the prehistoric past was a preferential selection for neoteny
, particularly in females. The idea that adult humans exhibit certain neotenous (juvenile) features, not evinced in the great apes, is about a century old. Louis Bolk
made a long list of such traits, and Stephen Jay Gould
published a short list in Ontogeny and Phylogeny
. In addition, paedomorphic characteristics in women are widely acknowledged as desirable by men. For instance, vellus hair is a juvenile characteristic. However, while men develop longer, coarser, thicker, and darker terminal hair
through sexual differentiation
, women do not, leaving their vellus hair visible.
By contrast, some intuit that tightly coiled hair that grows into a typical Afro-like formation would have greatly reduced the ability of the head and brain to cool. They reason that although hair density in African peoples is much less than their European counterparts, in the intense sun the effective 'woolly hat' produced would have been a disadvantage. However, anthropologists such as Nina Jablonski make the opposite argument with regards to this hair texture. Specifically, Jablonski's assertions suggest that the adjective "woolly" in reference to Afro-hair is a misnomer
to the extent that it connotes the high heat insulation derivable from the true wool of sheep. Instead, the relatively sparse density of Afro-hair, combined with its springy coils actually results in an airy, almost sponge-like effect. This, in turn, Jablonski argues, more likely facilitates an increase in the circulation of cool air onto the scalp. Further, Afro-hair does not respond as easily to moisture/sweat as straight hair. Thus it does not stick to the neck and scalp when wet. Rather, unless totally drenched, it tends to retain its basic springy puffiness. In this sense, the trait may enhance comfort levels in intense equatorial climates compared to straight hair (which, on the other hand, tends to naturally fall over the ears and neck to a degree that provides slightly enhanced comfort levels in cold climates relative to tightly coiled hair).
Further, some interpret the ideas of Charles Darwin as suggesting that some traits, such as hair texture, were so arbitrary to human survival that the role natural selection played was trivial. Hence, they argue in favor of his suggestion that sexual selection may be responsible for such traits. However, inclinations towards deeming hair texture "adaptively-trivial" may root in certain cultural value judgments more than objective logic. In this sense the possibility that hair texture may have played an adaptively-significant role cannot be completely eliminated from consideration. In fact, while the sexual selection hypothesis cannot be ruled out, the asymmetrical distribution of this trait vouches for environmental influence. Specifically, if hair texture were simply the result of adaptively arbitrary human aesthetic preferences, one would expect that the global distribution of the various hair textures would be fairly random. Instead, the distribution of Afro-hair is strongly skewed toward the equator. Further, it is notable that the most pervasive expression of this hair texture can be found in sub-Saharan Africa; a region of the world that abundant genetic and paleo-anthropological evidence suggests, was the relatively recent (~200,000 year old) point of origin for modern humanity. In fact, although genetic findings (Tishkoff, 2009) suggest that sub-Saharan Africans are the most genetically diverse continental group on Earth, Afro-textured hair approaches ubiquity in this region. This points to a strong, long-term selective pressure that, in stark contrast to most other regions of the genomes of sub-Saharan groups, left little room for genetic variation at the determining loci. Such a pattern, again, does not seem to support human sexual aesthetics as being the sole/primary cause of this distribution.
(which is essential for bone development) in response to said light.
In this sense, the evidence with regard to the evolution of straight hair texture seems to support Jablonski's suggestions that the need for vitamin D triggered the transition from dark to pale, translucent skin among modern humans. Specifically, the distribution of this trait suggests that this need may have (initially) grown so intense at certain (early) points that those among said (initially more deeply-pigmented skinned) Northern-migrants with mutations for straighter hair survived and had children at (somewhat) higher rates. This early change in texture was likely subsequently followed by the accumulation of adaptively-advantageous genetic changes that led to the above-mentioned skin-translucence. This argument is made based on the principle that straight fibers better facilitate the passage of UV light into the body relative to curly hair. It is substantiated by Iyengar's (1998) findings that UV light can pass through straight human hair roots in a manner similar to the way that light passes through fiber optic tubes (Iyengar, 1998).
Nonetheless, some argue against this stance because straighter hair ends tend to point downward while fiber optics requires that light be transmitted at a high angle to the normal of the inner reflective surface. In light of this, they suggest that only light reflected from the ground could successfully enter the hair follicle and be transmitted down the shaft. Even this process, they argue, is hindered by the curvature at the base of the hair. Therefore, coupled with the amount of skin covered by long head hair, these factors seem to militate against the adaptive usefulness of straight hair at northern latitudes. They further argue that UV light also is poorly reflected from soil and dull surfaces. These ideas can be countered by the fact that during the winter, the time of year in which UV light is most scarce at northern latitudes, the ground is often covered with white snow. Given that white is the most effective color in terms of facilitating the reflection of ground light, the hypothesis that straight hair could have been adaptively favorable, cannot be fully discounted in this regard. In addition, as mentioned in the previous section, straight hair also may have contributed to enhanced comfort levels in the north. This is evident in the extent to which, relative to curly hair, it tends to provide a layer of protection for ears and necks against the cold.
The latter hypothesis seems the more plausible evolution determinant as the surface area of the head is minute compared to the remainder of the body, thus the energy required in producing long hair for the express purpose of "optical" amplification of UV light reflected from the snow seems counterproductive (however, it's very likely that the trait was sustained due to a nuanced combination of multiple influences, given that human hunting-skills and ingenuity were such by 50,000 years ago that said benefits in terms of 'comfort' could have alternatively been derived from constructing fur head/ear warmers from prey, etc.). Scientists point to the fact that straight hair found in many ethnic groups is denser as well and has a greater ability to "show" as it does not coil, hence providing more warmth as the likely deterministic factor for the evolution of straight long hair. Some scientists argue that since the head and appendages are the greatest areas for heat loss from the body, the ability to grow long hair on the crown of the head as well as the face provides a distinct advantage in a cold climate. Since the main sensory organs are anatomically located on the head, long hair provides the necessary warmth and protection in a cold climate that allows the use of these organs by exposing them to the elements to "sense", in for example a hunt, yet still providing necessary warmth and protection to sustain prolonged exposure. It may be argued, therefore, that the ability to grow long, straight, densely packed hair provides a distinct evolutionary advantage in cold climate; however, it would be a distinct disadvantage in a hot climate, when compared to loosely packed, spongy, closely cropped hair.
. Specifically, the relevant findings indicate that the EDAR mutation coding for the predominant East Asian 'coarse' or thick, straight hair texture arose within the past ~65,000 years, which is a time frame that covers from the earliest of the 'Out of Africa' migrations up to now.
is almost always motivated by cosmetic reasons.
Depilation is the removal of hair from the surface of the skin. This can be achieved through methods such as shaving
. Epilation
is the removal of the entire hair strand, including the part of the hair that has not yet left the follicle. A popular way to epilate hair is through waxing
it.
is accomplished with bladed instruments, such as razors. The blade
is brought close to the skin and stroked over the hair in the desired area to cut the terminal hairs and leave the skin feeling smooth. Depending upon the rate of growth, one can begin to feel the hair growing back within hours of shaving. This is especially evident in men who develop a five o'clock shadow
after having shaved their faces. This new growth is called stubble
. Stubble typically appears to grow back thicker because the shaved hairs are blunted.
involves using a sticky wax and strip of paper or cloth to pull hair from the root. Waxing is the ideal hair removal technique to keep an area hair-free for long periods of time. It can take five to nine weeks for waxed hair to begin to resurface again. Hair in areas that have previously been waxed also is known to grow back finer and thinner, especially compared to hair that has been shaved with a razor.
or clippers
. People with longer hair will most often use scissors to cut their hair, whereas shorter hair is maintained using a trimmer. Depending on the desired length and overall health of the hair, periods without cutting or trimming the hair can vary.
Many people will confuse what a haircut is versus what a trim is. A haircut is usually performed in order to change one's hairstyle
, while a trim helps to keep away split ends
and keep the hair well-groomed. Cutting hair tends to take off more hair than trimming hair does. When hair is trimmed, only the first few centimeters need to be removed, whereas haircuts can sometimes result in the loss of many inches of hair.
, except on the palms of the hand
s and the soles of the feet (among other areas). Hair is most noticeable on most people in a small number of areas, which are also the ones that are most commonly trimmed, plucked
, or shaved
. These include the face
, ear
s, head
, eyebrows, leg
s, and armpits, as well as the pubic region. The highly visible differences between male and female body and facial hair are a notable secondary sex characteristic
.
is a sign of puberty
in men. White hair is a sign of age or genetics, which may be concealed with hair dye. Male pattern baldness
is a sign of age, which may be concealed with a toupee
, hats, or religious and cultural adornments. Although drugs and medical procedures exist for the treatment of baldness, many balding men simply shave their heads. Hair whorl
s have been discovered to be associated with brain development
.
Hairstyle
may be an indicator of group membership. During the English Civil War
, the followers of Oliver Cromwell
decided to crop their hair close to their head, as an act of defiance to the curls and ringlets of the king's men. This led to the Parliamentary faction being nicknamed Roundhead
s. Having bobbed hair
was popular among the flapper
s in the 1920s as a sign of rebellion against traditional roles for women. Female art students known as the "cropheads" also adopted the style, notably at the Slade School in London, England. Regional variations in hirsutism
cause practices regarding hair on the arms and legs to differ. Some religious groups may follow certain rules regarding hair as part of religious observance. The rules often differ for men and women.
Many subcultures have hairstyles which may indicate an unofficial membership. Many hippie
s, metalheads, and Indian sadhus have long hair
. Many punks
wear a hairstyle known as a Mohawk
or other spiked and dyed hairstyles; skinhead
s have short-cropped or completely shaved heads. Mullet
hairstyles stereotypically have been associated with redneck
s.
Heads were shaved in concentration camps, and head-shaving has been used as punishment
, especially for women with long hair. The shaven head is common in military
haircuts, while Western monks are known for the tonsure
. By contrast, among some Indian holy men, the hair is worn extremely long.
In the the time of Confucius (5th century BCE), the Chinese grew out their hair and often tied it, as a symbol of filial piety.
Regular hairdressing in some cultures is considered a sign of wealth or status. The dreadlocks
of the Rastafari movement
were despised early in the movement's history. In some cultures, having one's hair cut can symbolize a liberation from one's past, usually after a trying time in one's life. Cutting the hair also may be a sign of mourning.
Tightly coiled hair in its natural state may be worn in an Afro
. This hairstyle was once worn among African Americans as a symbol of racial pride. Given that the coiled texture is the natural state of some African Americans' hair, or perceived as being more "African", this simple style is now often seen as a sign of self-acceptance and an affirmation that the beauty norms of dominant (northern/European) culture are not absolute. It is important to note that African Americans as a whole have a variety of hair textures, as they are not an ethnically homogeneous group, but an ad-hoc of different ethnicities, one component being African. It is also important to note that Afro-textured hair is not universal in Africa as well, and hair texture varies among different African ethnicities.
The film Easy Rider
(1969) includes the assumption that the two main characters could have their long hairs forcibly shaved with a rusty razor when jailed, symbolizing the intolerance of some conservative groups toward members of the counterculture
.
At the conclusion of the Oz obscenity trials in the UK, the defendants had their heads shaved by the police, causing public outcry. During the appeal trial, they appeared in the dock wearing wigs.
, a common part of the hijab
in Islam
and a symbol of modesty required for certain religious rituals in Orthodox Christianity
. Russian Orthodox Church
requires all married women to wear headscarves inside the church; this tradition is often extended to all women, regardless of marital status. Orthodox Judaism
also commands the use of scarves and other head coverings for women for modesty reasons. Certain Hindu
sects also wear head scarves for religious reasons. Sikhs
generally keep their hair uncut and men keep it tied in a bun on the head, which is then covered appropriately using a turban
. Multiple religions, both ancient and contemporary, require or advise one to allow their hair to become dreadlocks
, though people also wear them for fashion. For men, Islam, Orthodox Judaism, Orthodox Christianity, Roman Catholicism and other religious groups have at various times recommended or required the covering of the head and sections of the hair of men, and some have dictates relating to the cutting of men's facial and head hair. Some Christian sects throughout history and up to modern times have also religiously proscribed the cutting of women's hair.
Protein filament
In biology, a filament is a "long chain of proteins, such as those found in hair, muscle, or in flagella". They are often bundled together for strength and rigidity. Some cellular examples include:*Actin filaments*Microtubules*Intermediate filaments...
ous biomaterial
Biomaterial
A biomaterial is any matter, surface, or construct that interacts with biological systems. The development of biomaterials, as a science, is about fifty years old. The study of biomaterials is called biomaterials science. It has experienced steady and strong growth over its history, with many...
, that grows from follicles
Hair follicle
A hair follicle is a skin organ that produces hair. Hair production occurs in phases, including a growth phase , and cessation phase , and a rest phase . Stem cells are principally responsible for the production of hair....
found in the dermis
Dermis
The dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...
. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
.
The human body, apart from its glabrous skin, is covered in follicles which produce thick terminal
Terminal hair
Terminal hairs are thick, long, and dark, as compared with vellus hair. During puberty, the increase in androgenic hormone levels causes vellus hair to be replaced with terminal hair in certain parts of the human body...
and fine vellus hair. Most common interest in hair is focused on hair growth, hair types and hair care
Hair care
Hair care is an overall term for parts of hygiene and cosmetology involving the hair on the human head. Hair care will differ according to one's hair type and according to various processes that can be applied to hair...
, but hair is also an important biomaterial
Biomaterial
A biomaterial is any matter, surface, or construct that interacts with biological systems. The development of biomaterials, as a science, is about fifty years old. The study of biomaterials is called biomaterials science. It has experienced steady and strong growth over its history, with many...
primarily composed of protein, notably keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
.
The word "hair" often refers to two distinct structures:
- the part beneath the skin, called the hair follicle or when pulled from the skin, called the bulb. This organ is located in the dermisDermisThe dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...
and maintains stem cells which not only re-grow the hair after it falls out, but also are recruited to regrow skin after a wound; - the shaft, which is the hard filamentous part that extends above the skin surface. A cross section of the hair shaft may be divided roughly into three zones.
Hair fibers have a structure consisting of several layers. Starting from the outside:
- the cuticle which consists of several layers of flat, thin cells laid out overlapping one another as roof shingles,
- the cortex, which contains the keratinKeratinKeratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
bundles in cell structures that remain roughly rod-like; and in some cases, - the medulla, a disorganized and open area at the fiber's center.
Description
Medulla (hair)
-Importance in forensics:Hair can easily be discredited as belonging to a human with the presence of medulla. Most other mammals possess one which is easily visible under a microscope. Humans of Middle-Eastern origin, however, do, in fact, possess a thin, less visible medulla...
, cortex
Cortex (hair)
The cortex of the hair shaft is located between the hair cuticle and medulla....
, and cuticle
Cuticle (hair)
The hair cuticle is the outermost part of the hair shaft. It is a hard shingle-like layer of overlapping cells, some five to twelve deep. It is formed from dead cells which form scales that gives the hair shaft strength and do the best job of providing protection for it...
. The innermost region, the medulla, is not always present and is an open, unstructured region. The highly structured and organized cortex, or middle layer of the hair, is the primary source of mechanical strength and water uptake. The cortex contains melanin
Melanin
Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...
, which colors the fiber based on the number, distribution and types of melanin granules. The shape of the follicle determines the shape of the cortex, and the shape of the fiber is related to how straight or curly the hair is. Asian hair typically has a round fiber and is quite straight. Oval and irregularly-shaped fibers are generally more wavy or even curly. The cuticle is the outer covering. Its complex structure slides as the hair swells and is covered with a single molecular layer of lipid that makes the hair repel water. The diameter of human hair varies from 17 um.
Hair growth begins inside the hair follicle
Hair follicle
A hair follicle is a skin organ that produces hair. Hair production occurs in phases, including a growth phase , and cessation phase , and a rest phase . Stem cells are principally responsible for the production of hair....
. The only "living" portion of the hair is found in the follicle. The hair that is visible is the hair shaft, which exhibits no biochemical activity and is considered "dead". The base of the root is called the bulb, which contains the cells that produce the hair shaft. Other structures of the hair follicle include the oil producing sebaceous gland
Sebaceous gland
The sebaceous glands are microscopic glands in the skin that secrete an oily/waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals...
which lubricates the hair and the erector pili muscles, which are responsible for causing hairs to stand up. In humans, with little body hair, the effect results in goose bumps
Goose bumps
Goose bumps, also called goose flesh, goose pimples, chill bumps, chicken skin, funky spots, Dasler Bumps, chicken bumps or the medical term cutis anserina, are the bumps on a person's skin at the base of body hairs which may involuntarily develop when a person is cold or experiences strong...
.
Natural Color
All natural hair colors are the result of two types of hair pigment. Both of these pigments are melanin types, produced inside the hair follicle and packed into granules found in the fibers. Eumelanin is the dominant pigment in dark-blond, brown, and black hair, while pheomelanin is dominant in red hair. Blond hair is the result of having little pigmentation in the hair strand. Gray hair occurs when melanin production decreases or stops.Human hair growth
Hair grows everywhere on the external body except for mucous membranes and glabrous skin, such as that found on the soles of the hands, feet, and lips.Hair follows a specific growth cycle with three distinct and concurrent phases: anagen, catagen, and telogen phases. Each has specific characteristics that determine the length of the hair. All three occur simultaneously; one strand of hair may be in the anagen phase, while another is in the telogen phase.
The body has different types of hair, including vellus hair and androgenic hair
Androgenic hair
Androgenic hair, colloquially body hair, is the terminal hair that develops on the body during and after puberty. It is differentiated from the head hair and less visible vellus hair, which are much finer and lighter in color. The growth of androgenic hair is related to the level of androgens in...
, each with its own type of cellular construction. The different construction gives the hair unique characteristics, serving specific purposes, mainly warmth and protection.
Function
Many mammals have furFur
Fur is a synonym for hair, used more in reference to non-human animals, usually mammals; particularly those with extensives body hair coverage. The term is sometimes used to refer to the body hair of an animal as a complete coat, also known as the "pelage". Fur is also used to refer to animal...
and other hairs that serve different functions. Hair provides thermal regulation and camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
for many animals; for others it provides signals to other animals such as warnings, mating, or other communicative displays; and for some animals hair provides defensive functions and, rarely, even offensive protection. Hair also has a sensory function, extending the sense of touch beyond the surface of the skin. Guard hairs give warnings that may trigger a recoiling reaction.
Warmth
While humans have developed clothing and other means of keeping warm, the hair found on the head serves as primary sources of heat insulationThermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...
and cooling (when sweat evaporates from soaked hair) as well as protection from ultra-violet radiation exposure. The function of hair in other locations is debated. Hats and coats are still required while doing outdoor activities in cold weather to prevent frostbite
Frostbite
Frostbite is the medical condition where localized damage is caused to skin and other tissues due to extreme cold. Frostbite is most likely to happen in body parts farthest from the heart and those with large exposed areas...
and hypothermia
Hypothermia
Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...
, but the hair on the human body does help to keep the internal temperature regulated. When the body is too cold, the arrector pili muscles found attached to hair follicles stand up, causing the hair in these follicles to do the same. These hairs then form a heat-trapping layer above the epidermis
Epidermis (zoology)
The Epidermis is an epithelium that covers the body of an eumetazoan . Eumetazoa have a cavity lined with a similar epithelium, the gastrodermis, which forms a boundary with the epidermis at the mouth.Sponges have no epithelium, and therefore no epidermis or gastrodermis...
. This process is formally called piloerection, derived from the Latin words 'pilus' ('hair') and 'erectio' ('stiffening'), but is more commonly known as 'having goose bumps
Goose bumps
Goose bumps, also called goose flesh, goose pimples, chill bumps, chicken skin, funky spots, Dasler Bumps, chicken bumps or the medical term cutis anserina, are the bumps on a person's skin at the base of body hairs which may involuntarily develop when a person is cold or experiences strong...
' in humans. This is more effective in other mammals whose fur fluffs up to create air pockets between hairs that insulate the body from the cold. The opposite actions occur when the body is too warm; The arrector muscles make the hair lay flat on the skin which allows heat to leave.
Protection
Human hair may not compete with the painful spines of the porcupinePorcupine
Porcupines are rodents with a coat of sharp spines, or quills, that defend or camouflage them from predators. They are indigenous to the Americas, southern Asia, and Africa. Porcupines are the third largest of the rodents, behind the capybara and the beaver. Most porcupines are about long, with...
, but much of the hair on the human body is suited to protect it. This natural armor cannot directly protect humans from potential predators, but it does help to keep the sense organs, such as the eyes, working properly.
Touch sense
Movements of hair shafts are detected by nerve receptors within the skin and by hair follicle receptors through displacement and vibration of hair shafts. Hairs can sense movements of air as well as touch by physical objects and are especially sensitive to the presence of insects. Some hairs, such as eyelashes, are especially sensitive to the presence of potentially harmful matter.Eyebrows and eyelashes
The eyebrowEyebrow
The eyebrow is an area of thick, delicate hairs above the eye that follows the shape of the lower margin of the brow ridges of some mammals. Their main function is to prevent sweat, water, and other debris from falling down into the eye socket, but they are also important to human communication and...
s provide some protection to the eyes from dirt
Dirt
Dirt is unclean matter, especially when in contact with a person's clothes, skin or possessions when they are said to become dirty. Common types of dirt include:* dust — a general powder of organic or mineral matter...
, sweat
SWEAT
SWEAT is an OLN/TSN show hosted by Julie Zwillich that aired in 2003-2004.Each of the 13 half-hour episodes of SWEAT features a different outdoor sport: kayaking, mountain biking, ice hockey, beach volleyball, soccer, windsurfing, rowing, Ultimate, triathlon, wakeboarding, snowboarding, telemark...
, and rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
. More importantly, they play a key role in non-verbal communication
Communication
Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...
. In many other mammals they contain much longer, whisker-like hairs that act as tactile sensors.
The eyelash
Eyelash
An eyelash or simply lash is one of the hairs that grow at the edge of the eyelid. Eyelashes protect the eye from debris and perform some of the same function as whiskers do on a cat or a mouse in the sense that they are sensitive to being touched, thus providing a warning that an object is near...
grows at the edges of the eyelid and protects the eye from dirt. The eyelash
Eyelash
An eyelash or simply lash is one of the hairs that grow at the edge of the eyelid. Eyelashes protect the eye from debris and perform some of the same function as whiskers do on a cat or a mouse in the sense that they are sensitive to being touched, thus providing a warning that an object is near...
is to humans, camels, horses, ostriches etc., what whiskers are to cats; they are used to sense when dirt, dust
Dust
Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...
, or any other potentially harmful object is too close to the eye. The eye reflexively closes as a result of this sensation.
Evolution
A 2008 study by the Medical University of ViennaMedical University of Vienna
The Medical University of Vienna is a medical university in Vienna, Austria.Formerly the faculty of medicine of the University of Vienna, became an independent university on January 1, 2004...
traced the origins of hair to the common ancestor of mammals, birds, and lizards that lived 310 million years ago. The study found chickens, lizards, and humans all possessed a similar set of genes that was involved in the production of alpha keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
. In chickens and lizards, the α-keratin produced was found in their claws, but in mammals it was used to produce hair. The scientists involved continued searching for the mechanisms that allowed mammals to use the keratins of animal claws to produce hair.
Human "hairlessness"
Humans seem hairless not because of a lack of follicles but because of the predominance of vellus fibers which are thinner, shorter, and more transparent than terminal fibers. The density of human hair follicles on the skin is about the average for an animal of equivalent size. In order to comprehend why humans are essentially hairless, it is essential to understand that mammalian body hair is not merely an aesthetic characteristic; it protects the skin from wounds, bites, cold temperatures, and UV radiation . Additionally, it can be used as a communication tool and as a camouflage . To this end, it can be concluded that benefits stemming from the loss of human body hair must be great enough to outweigh the loss of these protective functions by nakedness.Humans are the only primate species that have undergone significant hair loss and of the approximately 5000 extant species of mammal, only a handful are effectively hairless. This list includes elephants, rhinoceroses, hippopotamuses, walruses, pigs, whales and naked mole rats . Most mammals have light skin that is covered by fur, and biologists believe that early human ancestors started out this way also. Dark skin probably evolved after humans lost their body fur, because the naked skin was vulnerable to the strong UV radiation as would be experienced in Africa. Therefore, evidence of when human skin darkened has been used to date the loss of human body hair, assuming that the dark skin was needed after the fur was gone.
Dr. Alan R. Rogers, an evolutionary geneticist at the University of Utah, used mutations in the MC1R gene to estimate when human skin darkened. He said early humans may have gone through several genetic "clean sweeps" with light-skinned individuals dying off and dark-skinned individuals surviving. He estimates the last of these clean sweeps took place 1.2 million years ago. Therefore, apparent bareness in humans, likely has existed at least since that time. Later when humans began to live in more northerly latitudes, however, light skin became an advantage for the production of vitamin D
Vitamin D
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....
and the recessive gene began to become more prevalent in those populations.
Balding
Balding
Balding is a surname and may refer to :* Adam Balding , English rugby union player* Al Balding , Canadian golfer* Clare Balding , BBC sports presenter and journalist* David Balding, Australian statistician...
, where terminal hair
Terminal hair
Terminal hairs are thick, long, and dark, as compared with vellus hair. During puberty, the increase in androgenic hormone levels causes vellus hair to be replaced with terminal hair in certain parts of the human body...
switches to vellus hair, usually occurs at around thirty to forty years of age. In prehistoric times, most individuals were not as likely to live past 30, with few reaching their fourth decade, and thus it wasn't likely that this trait was subject to selection.
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
to the intense UV and sunlight at the equator, mostly by panting. Early hominids likely possessed fur similar to other large apes, but about 2.5 million years ago they developed a greater distribution of sweat glands that enabled them to perspire over most of the body. It is not clear whether the change in body hair appearance occurred before or after the development of sweat glands. Humans have eccrine sweat glands
Eccrine sweat glands
Eccrine glands are the major sweat glands of the human body, found in virtually all skin.. They produce a clear, odorless substance, consisting primarily of water and NaCl . NaCl is reabsorbed in the duct to reduce salt loss...
all over their bodies. Aside from the mammary glands that produce a specialized sweat called milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...
, most mammals just have apocrine sweat glands
Apocrine sweat glands
Apocrine sweat glands are sweat glands composed of a coiled secretory portion located at the junction of the dermis and subcutaneous fat, from which a straight portion inserts and secretes into the infundibular portion of the hair follicle...
on their armpits and loin. The rest of their body is covered in eccrine glands. There is a trend in primates to have increased eccrine sweat glands over the general surface of the body. It is unclear to what degree other primates sweat in response to heat, however.
The sweat glands in humans could have evolved to spread from the hands and feet as the body hair changed, or the hair change could have occurred to facilitate sweating. Horses and humans are two of the few animals capable of sweating on most of their body, yet horses are larger and still have fully developed fur. In humans, the skin hairs lie flat in hot conditions, as the erector pili muscles relax, preventing heat from being trapped by a layer of still air between the hairs, and increasing heat loss by convection.
Historically, some ideas have been advanced to explain the apparent hairlessness of humans, as compared to other species.
The thermoregulatory hypothesis (first proposed by Darwin in 1871 and later developed by Dr. Peter Wheeler, 1984, 1985) suggests that a need for decreased body hair originated as a response to climate change that began approximately 3 million years ago . At this time, the earth entered a period of global cooling that had a dehumidifying effect on the main early human habitats in East and Central Africa. Lush, wooded forests gave way to dry, grassland savannah; because of this, early humans were required to travel farther in search of food and water. As early humans diverged from their chimpanzee-lineage, they also became omnivorous in order to maximize calorie intake, an important distinction in a nutrient-scarce environment. Prey, however, are moving targets, and though early humans changed the traditionally ape-like appearance of the australopithecines and adapted long, strong legs to facilitate sustained running, dense, hairy coats still posed a potentially fatal risk of causing overheating during the chase . It is posited that thick hair got in the way of the sweat evaporating, so humans evolved a sparser coat of fur. Although hair provides protection against harmful UV radiation, since our hominin ancestors were bipedal, only our heads were exposed to the noonday sun. Humans kept the hair on our head which reflects harmful UV rays, but our body hair was reduced. The rise in eccrine glands occurred on the genes that determine the fate of epidermal stem cells in human embryonic development. Opponents of the thermoregulatory hypothesis would say that losing hair added an extreme weakness to cold, but, seeing as how humans figured out cutlery around 2.6 million years ago, our ancestors easily could have found clothing within the 1.4 million years between cutting up their kills and losing their hair.
The aquatic ape hypothesis
Aquatic ape hypothesis
The aquatic ape hypothesis is an alternative explanation of some characteristics of human evolution which hypothesizes that the common ancestors of modern humans spent a period of time adapting to life in a partially aquatic environment. The hypothesis is based on differences between humans and...
posits that sparsity of hair is an adaptation to a semi-aquatic environment, but the theory has yet to gain support among scientists.
Another hypothesis for the thick body hair on humans proposes that Fisherian runaway
Fisherian runaway
Fisherian runaway is a model of sexual selection, first proposed by R.A. Fisher in 1915, and expanded upon in his 1930 book The Genetical Theory of Natural Selection, that suggests an explanation for sexual selection of traits that do not obviously increase fitness of survival, based upon a...
sexual selection
Sexual selection
Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...
played a role (as well as in the selection of long head hair), (see types of hair and vellus hair), as well as a much larger role of testosterone in men. Sexual selection is the only theory thus far that explains the sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
seen in the hair patterns of men and women. On average, men have more body hair
Androgenic hair
Androgenic hair, colloquially body hair, is the terminal hair that develops on the body during and after puberty. It is differentiated from the head hair and less visible vellus hair, which are much finer and lighter in color. The growth of androgenic hair is related to the level of androgens in...
than women. Males have more terminal hair
Terminal hair
Terminal hairs are thick, long, and dark, as compared with vellus hair. During puberty, the increase in androgenic hormone levels causes vellus hair to be replaced with terminal hair in certain parts of the human body...
, especially on the face
Facial hair
Facial hair is a secondary sex characteristic of human males. Men often start developing facial hair in the later years of puberty or adolescence, approximately between 17–20 years of age, and most do not finish developing a fully adult beard until their early 20s or even later...
, chest
Chest hair
The term chest hair is generally used to describe hair that grows on the chest of human males, in the region between the neck and the abdomen. Chest hair, which is a secondary sex characteristic, develops during and after puberty...
, abdomen
Abdominal hair
The term abdominal hair refers to the hair that grows on the abdomen of humans and non-human mammals, in the region between the pubic area and the thorax . The growth of abdominal hair follows the same pattern on nearly all mammals, vertically from the pubic area upwards and from the thorax...
, and back, and females have more vellus hair, which is less visible. The halting of hair development at a juvenile stage, vellus hair, would also be consistent with the neoteny
Neoteny
Neoteny , also called juvenilization , is one of the two ways by which paedomorphism can arise. Paedomorphism is the retention by adults of traits previously seen only in juveniles, and is a subject studied in the field of developmental biology. In neoteny, the physiological development of an...
evident in humans, especially in females, and thus they could have occurred at the same time.. This theory, however, has significant holdings in today's cultural norms. There is no evidence that sexual selection would proceed to such a drastic extent over a million years ago when a full, lush coat of hair would most likely indicate health and would therefore be more likely to be selected for, not against.
A final hypothesis is that human hair was reduced in response to ectoparasites. The “ectoparasite” explanation of modern human nakedness is based on the principle that a hairless primate would harbor fewer parasites. When our ancestors adopted group-dwelling social arrangements roughly 1.8 mya, ectoparasite loads increased dramatically. Early humans became the only one of the 193 primate species to have flees, which can be attributed to the close living arrangements of large groups of individuals. While primate species have communal sleeping arrangements, these groups are always on the move and thus are less likely to harbor ectoparasites. Because of this, selection pressure for early humans would favor decreasing body hair because those with thick coats would have more lethal-disease-carrying ectoparasites and would thereby have lower fitness. Additional evidence for this hypothesis comes from studies that show that most ectoparasites on modern humans are confined to the head and pubic regions. Early humans were able to compensate for the loss of warmth and protection provided by body hair with subcutaneous fat and clothing. Hairlessness could maintained in modern society by sexual selection for hairless partners in addition to natural selection to reduce parasite loads.
Evolutionary variation
Evolutionary biologists suggest that the genus Homo arose in East AfricaEast Africa
East Africa or Eastern Africa is the easterly region of the African continent, variably defined by geography or geopolitics. In the UN scheme of geographic regions, 19 territories constitute Eastern Africa:...
approximately 2.5 million years ago. They devised new hunting techniques. The higher protein diet led to the evolution of larger body and brain sizes. Jablonski postulates that increasing body size, in conjunction with intensified hunting during the day at the equator, gave rise to a greater need to rapidly expel heat. As a result, humans evolved the ability to sweat: a process which was facilitated by the loss of body hair. A major problem with this theory, however, is that it does not explain why males are larger, hairier, and were more active in hunting than females. The female-male size differential among other closely associated primates is much greater than among humans, however, so it might have been reduced during evolution.
Other primates have sweat gland in their armpits that function as those of humans, and thus it is probable that human sweat glands evolved from a similar distribution, spreading to more areas of the body, rather than occurring through evolution of a new trait. It is not known whether the increased distribution of sweat glands occurred before, during, or after, the change in body hair, or even whether the two are related developments. Horses also sweat, and they are larger, hairier, and expend more energy running than human males, so there may not be any connection between the ability to sweat and the apparent hairlessness of humans.
Another factor in human evolution that also occurred in the prehistoric past was a preferential selection for neoteny
Neoteny
Neoteny , also called juvenilization , is one of the two ways by which paedomorphism can arise. Paedomorphism is the retention by adults of traits previously seen only in juveniles, and is a subject studied in the field of developmental biology. In neoteny, the physiological development of an...
, particularly in females. The idea that adult humans exhibit certain neotenous (juvenile) features, not evinced in the great apes, is about a century old. Louis Bolk
Louis Bolk
Lodewijk 'Louis' Bolk was a Dutch anatomist who created the fetalization theory about the human body. It states that when a human being is born, it is still a fetus, as can be seen if one pays attention to its big head, to its uncoordinated motility or to its absolute helplessness, for instance...
made a long list of such traits, and Stephen Jay Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....
published a short list in Ontogeny and Phylogeny
Ontogeny and Phylogeny (book)
Ontogeny and Phylogeny is Stephen Jay Gould's first technical book, published in 1977 by Belknap, a division of Harvard University Press. Gould wrote that Ernst Mayr suggested in passing that he write the book, but that "I only began it as a practice run to learn the style of lengthy exposition...
. In addition, paedomorphic characteristics in women are widely acknowledged as desirable by men. For instance, vellus hair is a juvenile characteristic. However, while men develop longer, coarser, thicker, and darker terminal hair
Terminal hair
Terminal hairs are thick, long, and dark, as compared with vellus hair. During puberty, the increase in androgenic hormone levels causes vellus hair to be replaced with terminal hair in certain parts of the human body...
through sexual differentiation
Sexual differentiation
Sexual differentiation is the process of development of the differences between males and females from an undifferentiated zygote...
, women do not, leaving their vellus hair visible.
Curly hair
Jablonski asserts that it was evolutionarily advantageous for pre-humans to retain the hair on their heads in order to protect the scalp as they walked upright in the intense African (equatorial) UV light. While some might argue that, by this logic, humans should also express hairy shoulders given that these body parts would putatively be exposed to similar conditions, the protection of the head, the seat of the brain that enabled humanity to become one of the most successful species on the planet (and which also is very vulnerable at birth), was arguably a more urgent issue (axillary hair in the underarms and groin were also retained as signs of sexual maturity). During the gradual process by which Homo erectus made a transition from furry to naked skin, their hair texture putatively changed gradually from straight (the condition of most mammals, including humanity's closest cousins—chimpanzees), to Afro-textured hair or 'kinky' (i.e. tightly coiled). This argument is based on the principle that curly hair impedes the passage of UV light into the body relative to straight hair (thus curly and/or coiled hair would be particularly advantageous for pale-skinned hominids living at the equator). It is substantiated by Iyengar's (1998) findings that UV light can enter into straight human hair roots (and thus into the body/skin) via the hair shaft. Specifically, the results of this study suggest that this phenomenon occurs in a manner similar to the way that light passes through fiber optic tubes (which do not function as effectively when kinked/sharply-curved/coiled). In this sense, during the period in which hominids (i.e. Homo Erectus) were gradually losing their straight body hair and thereby exposing the initially pale skin underneath their fur to the sun, straight hair would have been an adaptive liability. Hence, tightly coiled or 'kinky' Afro-hair may have (initially) evolved to prevent the entry of UV light into the body during the transition toward dark, UV-protected skin.By contrast, some intuit that tightly coiled hair that grows into a typical Afro-like formation would have greatly reduced the ability of the head and brain to cool. They reason that although hair density in African peoples is much less than their European counterparts, in the intense sun the effective 'woolly hat' produced would have been a disadvantage. However, anthropologists such as Nina Jablonski make the opposite argument with regards to this hair texture. Specifically, Jablonski's assertions suggest that the adjective "woolly" in reference to Afro-hair is a misnomer
Misnomer
A misnomer is a term which suggests an interpretation that is known to be untrue. Such incorrect terms sometimes derive their names because of the form, action, or origin of the subject becoming named popularly or widely referenced—long before their true natures were known.- Sources of misnomers...
to the extent that it connotes the high heat insulation derivable from the true wool of sheep. Instead, the relatively sparse density of Afro-hair, combined with its springy coils actually results in an airy, almost sponge-like effect. This, in turn, Jablonski argues, more likely facilitates an increase in the circulation of cool air onto the scalp. Further, Afro-hair does not respond as easily to moisture/sweat as straight hair. Thus it does not stick to the neck and scalp when wet. Rather, unless totally drenched, it tends to retain its basic springy puffiness. In this sense, the trait may enhance comfort levels in intense equatorial climates compared to straight hair (which, on the other hand, tends to naturally fall over the ears and neck to a degree that provides slightly enhanced comfort levels in cold climates relative to tightly coiled hair).
Further, some interpret the ideas of Charles Darwin as suggesting that some traits, such as hair texture, were so arbitrary to human survival that the role natural selection played was trivial. Hence, they argue in favor of his suggestion that sexual selection may be responsible for such traits. However, inclinations towards deeming hair texture "adaptively-trivial" may root in certain cultural value judgments more than objective logic. In this sense the possibility that hair texture may have played an adaptively-significant role cannot be completely eliminated from consideration. In fact, while the sexual selection hypothesis cannot be ruled out, the asymmetrical distribution of this trait vouches for environmental influence. Specifically, if hair texture were simply the result of adaptively arbitrary human aesthetic preferences, one would expect that the global distribution of the various hair textures would be fairly random. Instead, the distribution of Afro-hair is strongly skewed toward the equator. Further, it is notable that the most pervasive expression of this hair texture can be found in sub-Saharan Africa; a region of the world that abundant genetic and paleo-anthropological evidence suggests, was the relatively recent (~200,000 year old) point of origin for modern humanity. In fact, although genetic findings (Tishkoff, 2009) suggest that sub-Saharan Africans are the most genetically diverse continental group on Earth, Afro-textured hair approaches ubiquity in this region. This points to a strong, long-term selective pressure that, in stark contrast to most other regions of the genomes of sub-Saharan groups, left little room for genetic variation at the determining loci. Such a pattern, again, does not seem to support human sexual aesthetics as being the sole/primary cause of this distribution.
Straight hair
According to the recent single origin hypothesis, anatomically modern humans arose in East Africa approximately 200,000 years ago. Then, ~150,000 years later (i.e. around 50,000 years ago), sub-groups of this population began to expand our species' range to regions outside of, and (later) within, this continent (Tishkoff, 1996). For those members of this group who migrated far north (i.e. to northern Eurasia, etc.), the UV light of these regions was too weak to penetrate the highly pigmented skin of the initially (relatively) dark-skinned migrants so as to provide enough vitamin D for healthy bone development. Malformed bones in the pelvic area were especially deadly for women because they interfered with the successful delivery of babies, leading to the death of both the mother and the infant during labor. Hence, those with less pigmented skin survived and had children at higher rates because their skin allowed more UV light for the production of vitamin D. Thus, the skin of those in the group that left the African continent and went far north gradually developed adaptations for relatively greater translucence compared to equatorial hues. This enabled the passage of more UV light into the body at high latitudes, facilitating the natural human body-process of manufacturing vitamin DVitamin D
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....
(which is essential for bone development) in response to said light.
In this sense, the evidence with regard to the evolution of straight hair texture seems to support Jablonski's suggestions that the need for vitamin D triggered the transition from dark to pale, translucent skin among modern humans. Specifically, the distribution of this trait suggests that this need may have (initially) grown so intense at certain (early) points that those among said (initially more deeply-pigmented skinned) Northern-migrants with mutations for straighter hair survived and had children at (somewhat) higher rates. This early change in texture was likely subsequently followed by the accumulation of adaptively-advantageous genetic changes that led to the above-mentioned skin-translucence. This argument is made based on the principle that straight fibers better facilitate the passage of UV light into the body relative to curly hair. It is substantiated by Iyengar's (1998) findings that UV light can pass through straight human hair roots in a manner similar to the way that light passes through fiber optic tubes (Iyengar, 1998).
Nonetheless, some argue against this stance because straighter hair ends tend to point downward while fiber optics requires that light be transmitted at a high angle to the normal of the inner reflective surface. In light of this, they suggest that only light reflected from the ground could successfully enter the hair follicle and be transmitted down the shaft. Even this process, they argue, is hindered by the curvature at the base of the hair. Therefore, coupled with the amount of skin covered by long head hair, these factors seem to militate against the adaptive usefulness of straight hair at northern latitudes. They further argue that UV light also is poorly reflected from soil and dull surfaces. These ideas can be countered by the fact that during the winter, the time of year in which UV light is most scarce at northern latitudes, the ground is often covered with white snow. Given that white is the most effective color in terms of facilitating the reflection of ground light, the hypothesis that straight hair could have been adaptively favorable, cannot be fully discounted in this regard. In addition, as mentioned in the previous section, straight hair also may have contributed to enhanced comfort levels in the north. This is evident in the extent to which, relative to curly hair, it tends to provide a layer of protection for ears and necks against the cold.
The latter hypothesis seems the more plausible evolution determinant as the surface area of the head is minute compared to the remainder of the body, thus the energy required in producing long hair for the express purpose of "optical" amplification of UV light reflected from the snow seems counterproductive (however, it's very likely that the trait was sustained due to a nuanced combination of multiple influences, given that human hunting-skills and ingenuity were such by 50,000 years ago that said benefits in terms of 'comfort' could have alternatively been derived from constructing fur head/ear warmers from prey, etc.). Scientists point to the fact that straight hair found in many ethnic groups is denser as well and has a greater ability to "show" as it does not coil, hence providing more warmth as the likely deterministic factor for the evolution of straight long hair. Some scientists argue that since the head and appendages are the greatest areas for heat loss from the body, the ability to grow long hair on the crown of the head as well as the face provides a distinct advantage in a cold climate. Since the main sensory organs are anatomically located on the head, long hair provides the necessary warmth and protection in a cold climate that allows the use of these organs by exposing them to the elements to "sense", in for example a hunt, yet still providing necessary warmth and protection to sustain prolonged exposure. It may be argued, therefore, that the ability to grow long, straight, densely packed hair provides a distinct evolutionary advantage in cold climate; however, it would be a distinct disadvantage in a hot climate, when compared to loosely packed, spongy, closely cropped hair.
The EDAR Locus
A group of studies have recently shown that genetic patterns at the EDAR locus, a region of the modern human genome that contributes to hair texture variation among most individuals of East Asian descent, support the hypothesis that (East Asian) straight hair likely developed in this branch of the modern human lineage subsequent to the original expression of tightly coiled natural afro-hairNatural afro-hair
Afro-textured hair is a term used to refer to the natural texture of Black African hair that has not been altered by hot combs, flat irons, or chemicals ....
. Specifically, the relevant findings indicate that the EDAR mutation coding for the predominant East Asian 'coarse' or thick, straight hair texture arose within the past ~65,000 years, which is a time frame that covers from the earliest of the 'Out of Africa' migrations up to now.
Removal practices
Even though growing hair is an inevitable part of being human, it is becoming a concern to many individuals, especially young adults who believe that it is unsightly and should be removed. Hair removalHair removal
Hair removal is the removal of body hair, and describes the methods used to achieve that result.Hair typically grows all over the human body during and after puberty. Men tend to have more body hair than women. Both men and women tend to have hair on the head, eyebrows, eyelashes, armpits, pubic...
is almost always motivated by cosmetic reasons.
Depilation is the removal of hair from the surface of the skin. This can be achieved through methods such as shaving
Shaving
Shaving is the removal of hair, by using a razor or any other kind of bladed implement, to slice it down to the level of the skin. Shaving is most commonly practiced by men to remove their facial hair and by women to remove their leg and underarm hair...
. Epilation
EPilation
EPilation is the first full-length release from Brisbane musician Tara Simmons. Although a full-length, EPilation contains no new material and is a compilation of Tara's first two EPs Pendulum and All The Amendments...
is the removal of the entire hair strand, including the part of the hair that has not yet left the follicle. A popular way to epilate hair is through waxing
Waxing
Waxing is a method of semi-permanent hair removal which removes the hair from the root. New hair will not grow back in the previously waxed area for two to eight weeks, although some people will start to see regrowth in only a week. Almost any area of the body can be waxed, including eyebrows,...
it.
Shaving
ShavingShaving
Shaving is the removal of hair, by using a razor or any other kind of bladed implement, to slice it down to the level of the skin. Shaving is most commonly practiced by men to remove their facial hair and by women to remove their leg and underarm hair...
is accomplished with bladed instruments, such as razors. The blade
Blade
A blade is that portion of a tool, weapon, or machine with a cutting edge and/or a pointed tip that is designed to cut and/or puncture, stab, slash, chop, slice, thrust, or scrape animate or inanimate surfaces or materials...
is brought close to the skin and stroked over the hair in the desired area to cut the terminal hairs and leave the skin feeling smooth. Depending upon the rate of growth, one can begin to feel the hair growing back within hours of shaving. This is especially evident in men who develop a five o'clock shadow
Five O'Clock Shadow
Five O'Clock Shadow is an a cappella group from Boston, Massachusetts, that has been in existence since 1991. The band has performed on FOX News, A&E Network, ABC, ESPN and VH-1's "breakthrough" series. They have released 4 cassettes and 5 CDs, winning many Contemporary A cappella Recording...
after having shaved their faces. This new growth is called stubble
Stubble
Stubble is the regrowth of shaven hair, when it is short and has a rough, abrasive texture.-Facial:During the 1980s, facial stubble on men became fashionable, partly due to being popularized by the singer George Michael, as well as Miami Vice. This was also known as designer stubble and was...
. Stubble typically appears to grow back thicker because the shaved hairs are blunted.
Waxing
WaxingWaxing
Waxing is a method of semi-permanent hair removal which removes the hair from the root. New hair will not grow back in the previously waxed area for two to eight weeks, although some people will start to see regrowth in only a week. Almost any area of the body can be waxed, including eyebrows,...
involves using a sticky wax and strip of paper or cloth to pull hair from the root. Waxing is the ideal hair removal technique to keep an area hair-free for long periods of time. It can take five to nine weeks for waxed hair to begin to resurface again. Hair in areas that have previously been waxed also is known to grow back finer and thinner, especially compared to hair that has been shaved with a razor.
Cutting and trimming
Because the hair on the head is normally longer than other types of body hair, it is cut with scissorsScissors
Scissors are hand-operated cutting instruments. They consist of a pair of metal blades pivoted so that the sharpened edges slide against each other when the handles opposite to the pivot are closed. Scissors are used for cutting various thin materials, such as paper, cardboard, metal foil, thin...
or clippers
Manual hair clippers
Hair clippers are specialized implements used to cut human head hair. They work on the same principle as scissors, but are distinct from scissors themselves and razors...
. People with longer hair will most often use scissors to cut their hair, whereas shorter hair is maintained using a trimmer. Depending on the desired length and overall health of the hair, periods without cutting or trimming the hair can vary.
Many people will confuse what a haircut is versus what a trim is. A haircut is usually performed in order to change one's hairstyle
Hairstyle
A hairstyle, hairdo, or haircut refers to the styling of hair, usually on the human head. The fashioning of hair can be considered an aspect of personal grooming, fashion, and cosmetics, although practical, cultural, and popular considerations also influence some hairstyles.-History of...
, while a trim helps to keep away split ends
Split Ends
-TV:*Split Ends , a sitcom produced on ITV*Split Ends , a reality show on Style Network-Other:* split ends, the splitting or fraying of hair — see Trichoptilosis...
and keep the hair well-groomed. Cutting hair tends to take off more hair than trimming hair does. When hair is trimmed, only the first few centimeters need to be removed, whereas haircuts can sometimes result in the loss of many inches of hair.
Social role
Hair has great social significance for human beings. It can grow on most external areas of the human bodyHuman body
The human body is the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs.By the time the human reaches adulthood, the body consists of close to 100 trillion cells, the basic unit of life...
, except on the palms of the hand
Hand
A hand is a prehensile, multi-fingered extremity located at the end of an arm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs...
s and the soles of the feet (among other areas). Hair is most noticeable on most people in a small number of areas, which are also the ones that are most commonly trimmed, plucked
Plucking (hair removal)
Plucking or tweezing can mean the process of removing human hair, animal hair or a bird's feathers by mechanically pulling the item from the owner's body.In humans, this is done for personal grooming purposes, usually with tweezers...
, or shaved
Shaving
Shaving is the removal of hair, by using a razor or any other kind of bladed implement, to slice it down to the level of the skin. Shaving is most commonly practiced by men to remove their facial hair and by women to remove their leg and underarm hair...
. These include the face
Face
The face is a central sense organ complex, for those animals that have one, normally on the ventral surface of the head, and can, depending on the definition in the human case, include the hair, forehead, eyebrow, eyelashes, eyes, nose, ears, cheeks, mouth, lips, philtrum, temple, teeth, skin, and...
, ear
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
s, head
Human head
In human anatomy, the head is the upper portion of the human body. It supports the face and is maintained by the skull, which itself encloses the brain.-Cultural importance:...
, eyebrows, leg
Human leg
The human leg is the entire lower extremity or limb of the human body, including the foot, thigh and even the hip or gluteal region; however, the precise definition in human anatomy refers only to the section of the lower limb extending from the knee to the ankle.Legs are used for standing,...
s, and armpits, as well as the pubic region. The highly visible differences between male and female body and facial hair are a notable secondary sex characteristic
Secondary sex characteristic
Secondary sex characteristics are features that distinguish the two sexes of a species, but that are not directly part of the reproductive system. They are believed to be the product of sexual selection for traits which give an individual an advantage over its rivals in courtship and aggressive...
.
Indication of status
Healthy hair indicates health and youth (important in evolutionary biology). Hair colour and texture can be a sign of ethnic ancestry. Facial hairFacial hair
Facial hair is a secondary sex characteristic of human males. Men often start developing facial hair in the later years of puberty or adolescence, approximately between 17–20 years of age, and most do not finish developing a fully adult beard until their early 20s or even later...
is a sign of puberty
Puberty
Puberty is the process of physical changes by which a child's body matures into an adult body capable of reproduction, as initiated by hormonal signals from the brain to the gonads; the ovaries in a girl, the testes in a boy...
in men. White hair is a sign of age or genetics, which may be concealed with hair dye. Male pattern baldness
Baldness
Baldness implies partial or complete lack of hair and can be understood as part of the wider topic of "hair thinning". The degree and pattern of baldness can vary greatly, but its most common cause is male and female pattern baldness, also known as androgenic alopecia, alopecia androgenetica or...
is a sign of age, which may be concealed with a toupee
Toupee
A toupée is a hairpiece or partial wig of natural or synthetic hair worn to cover partial baldness or for theatrical purposes. While toupées and hairpieces are typically associated with male wearers, some women also use hairpieces to lengthen existing hair, or cover partially exposed scalp...
, hats, or religious and cultural adornments. Although drugs and medical procedures exist for the treatment of baldness, many balding men simply shave their heads. Hair whorl
Hair whorl
A hair whorl is a patch of hair growing in the opposite direction of the rest of the hair. Hair whorls occur in most hairy animals, on the body as well as on the head. Hair whorls, also known as crowns, swirls, trichoglyphs, or cowlicks, can be either clockwise or counterclockwise in direction of...
s have been discovered to be associated with brain development
Neural development
Neural development comprises the processes that generate, shape, and reshape the nervous system, from the earliest stages of embryogenesis to the final years of life. The study of neural development aims to describe the cellular basis of brain development and to address the underlying mechanisms...
.
Hairstyle
Hairstyle
A hairstyle, hairdo, or haircut refers to the styling of hair, usually on the human head. The fashioning of hair can be considered an aspect of personal grooming, fashion, and cosmetics, although practical, cultural, and popular considerations also influence some hairstyles.-History of...
may be an indicator of group membership. During the English Civil War
English Civil War
The English Civil War was a series of armed conflicts and political machinations between Parliamentarians and Royalists...
, the followers of Oliver Cromwell
Oliver Cromwell
Oliver Cromwell was an English military and political leader who overthrew the English monarchy and temporarily turned England into a republican Commonwealth, and served as Lord Protector of England, Scotland, and Ireland....
decided to crop their hair close to their head, as an act of defiance to the curls and ringlets of the king's men. This led to the Parliamentary faction being nicknamed Roundhead
Roundhead
"Roundhead" was the nickname given to the supporters of the Parliament during the English Civil War. Also known as Parliamentarians, they fought against King Charles I and his supporters, the Cavaliers , who claimed absolute power and the divine right of kings...
s. Having bobbed hair
Bob cut
A "bob cut" is a short haircut for women in which the hair is typically cut straight around the head at about jaw-level, often with a fringe at the front.-The beginning:...
was popular among the flapper
Flapper
Flapper in the 1920s was a term applied to a "new breed" of young Western women who wore short skirts, bobbed their hair, listened to jazz, and flaunted their disdain for what was then considered acceptable behavior...
s in the 1920s as a sign of rebellion against traditional roles for women. Female art students known as the "cropheads" also adopted the style, notably at the Slade School in London, England. Regional variations in hirsutism
Hirsutism
Hirsutism or frazonism is the excessive hairiness on women in those parts of the body where terminal hair does not normally occur or is minimal - for example, a beard or chest hair. It refers to a male pattern of body hair and it is therefore primarily of cosmetic and psychological concern...
cause practices regarding hair on the arms and legs to differ. Some religious groups may follow certain rules regarding hair as part of religious observance. The rules often differ for men and women.
Many subcultures have hairstyles which may indicate an unofficial membership. Many hippie
Hippie
The hippie subculture was originally a youth movement that arose in the United States during the mid-1960s and spread to other countries around the world. The etymology of the term 'hippie' is from hipster, and was initially used to describe beatniks who had moved into San Francisco's...
s, metalheads, and Indian sadhus have long hair
Long hair
Long hair is a hairstyle. Exactly what constitutes long hair can change from culture to culture, or even within cultures. For example, a woman with chin-length hair in some cultures may be said to have short hair, while a man with the same length of hair in some of the same cultures would be said...
. Many punks
Punk fashion
Punk fashion is the clothing, hairstyles, cosmetics, jewelry, and body modifications of the punk subculture. Punk fashion varies widely, ranging from Vivienne Westwood designs to styles modeled on bands like The Exploited. The distinct social dress of other subcultures and art movements, including...
wear a hairstyle known as a Mohawk
Mohawk hairstyle
The mohawk is a hairstyle in which, in the most common variety, both sides of the head are shaven, leaving a strip of noticeably longer hair...
or other spiked and dyed hairstyles; skinhead
Skinhead
A skinhead is a member of a subculture that originated among working class youths in the United Kingdom in the 1960s, and then spread to other parts of the world. Named for their close-cropped or shaven heads, the first skinheads were greatly influenced by West Indian rude boys and British mods,...
s have short-cropped or completely shaved heads. Mullet
Mullet (haircut)
The mullet is a hairstyle that is short at the front and sides, and long in the back. . The mullet began to appear in popular media in the 1960s and 1970s but did not become generally well-known until the early 1980s...
hairstyles stereotypically have been associated with redneck
Redneck
Redneck is a historically derogatory slang term used in reference to poor, uneducated white farmers, especially from the southern United States...
s.
Heads were shaved in concentration camps, and head-shaving has been used as punishment
Punishment
Punishment is the authoritative imposition of something negative or unpleasant on a person or animal in response to behavior deemed wrong by an individual or group....
, especially for women with long hair. The shaven head is common in military
Military
A military is an organization authorized by its greater society to use lethal force, usually including use of weapons, in defending its country by combating actual or perceived threats. The military may have additional functions of use to its greater society, such as advancing a political agenda e.g...
haircuts, while Western monks are known for the tonsure
Tonsure
Tonsure is the traditional practice of Christian churches of cutting or shaving the hair from the scalp of clerics, monastics, and, in the Eastern Orthodox Church, all baptized members...
. By contrast, among some Indian holy men, the hair is worn extremely long.
In the the time of Confucius (5th century BCE), the Chinese grew out their hair and often tied it, as a symbol of filial piety.
Regular hairdressing in some cultures is considered a sign of wealth or status. The dreadlocks
Dreadlocks
Dreadlocks, also called locks, a ras, dreads, "rasta" or Jata , are matted coils of hair. Dreadlocks are usually intentionally formed; because of the variety of different hair textures, various methods are used to encourage the formation of locks such as backcombing...
of the Rastafari movement
Rastafari movement
The Rastafari movement or Rasta is a new religious movement that arose in the 1930s in Jamaica, which at the time was a country with a predominantly Christian culture where 98% of the people were the black descendants of slaves. Its adherents worship Haile Selassie I, Emperor of Ethiopia , as God...
were despised early in the movement's history. In some cultures, having one's hair cut can symbolize a liberation from one's past, usually after a trying time in one's life. Cutting the hair also may be a sign of mourning.
Tightly coiled hair in its natural state may be worn in an Afro
Afro
Afro, sometimes shortened to fro and also known as a "natural", is a hairstyle worn naturally by people with lengthy kinky hair texture or specifically styled in such a fashion by individuals with naturally curly or straight hair...
. This hairstyle was once worn among African Americans as a symbol of racial pride. Given that the coiled texture is the natural state of some African Americans' hair, or perceived as being more "African", this simple style is now often seen as a sign of self-acceptance and an affirmation that the beauty norms of dominant (northern/European) culture are not absolute. It is important to note that African Americans as a whole have a variety of hair textures, as they are not an ethnically homogeneous group, but an ad-hoc of different ethnicities, one component being African. It is also important to note that Afro-textured hair is not universal in Africa as well, and hair texture varies among different African ethnicities.
The film Easy Rider
Easy Rider
Easy Rider is a 1969 American road movie written by Peter Fonda, Dennis Hopper, and Terry Southern, produced by Fonda and directed by Hopper. It tells the story of two bikers who travel through the American Southwest and South with the aim of achieving freedom...
(1969) includes the assumption that the two main characters could have their long hairs forcibly shaved with a rusty razor when jailed, symbolizing the intolerance of some conservative groups toward members of the counterculture
Counterculture
Counterculture is a sociological term used to describe the values and norms of behavior of a cultural group, or subculture, that run counter to those of the social mainstream of the day, the cultural equivalent of political opposition. Counterculture can also be described as a group whose behavior...
.
At the conclusion of the Oz obscenity trials in the UK, the defendants had their heads shaved by the police, causing public outcry. During the appeal trial, they appeared in the dock wearing wigs.
Religious practices
Women's hair may be hidden using headscarvesHeadscarf
Headscarves or head scarves are scarves covering most or all of the top of a woman's hair and her head. Headscarves may be worn for a variety of purposes, such as for warmth, for sanitation, for fashion or social distinction; with religious significance, to hide baldness, out of modesty, or other...
, a common part of the hijab
Hijab
The word "hijab" or "'" refers to both the head covering traditionally worn by Muslim women and modest Muslim styles of dress in general....
in Islam
Islam
Islam . The most common are and . : Arabic pronunciation varies regionally. The first vowel ranges from ~~. The second vowel ranges from ~~~...
and a symbol of modesty required for certain religious rituals in Orthodox Christianity
Orthodox Christianity
The term Orthodox Christianity may refer to:* the Eastern Orthodox Church and its various geographical subdivisions...
. Russian Orthodox Church
Russian Orthodox Church
The Russian Orthodox Church or, alternatively, the Moscow Patriarchate The ROC is often said to be the largest of the Eastern Orthodox churches in the world; including all the autocephalous churches under its umbrella, its adherents number over 150 million worldwide—about half of the 300 million...
requires all married women to wear headscarves inside the church; this tradition is often extended to all women, regardless of marital status. Orthodox Judaism
Orthodox Judaism
Orthodox Judaism , is the approach to Judaism which adheres to the traditional interpretation and application of the laws and ethics of the Torah as legislated in the Talmudic texts by the Sanhedrin and subsequently developed and applied by the later authorities known as the Gaonim, Rishonim, and...
also commands the use of scarves and other head coverings for women for modesty reasons. Certain Hindu
Hindu
Hindu refers to an identity associated with the philosophical, religious and cultural systems that are indigenous to the Indian subcontinent. As used in the Constitution of India, the word "Hindu" is also attributed to all persons professing any Indian religion...
sects also wear head scarves for religious reasons. Sikhs
Sikhism
Sikhism is a monotheistic religion founded during the 15th century in the Punjab region, by Guru Nanak Dev and continued to progress with ten successive Sikh Gurus . It is the fifth-largest organized religion in the world and one of the fastest-growing...
generally keep their hair uncut and men keep it tied in a bun on the head, which is then covered appropriately using a turban
Turban
In English, Turban refers to several types of headwear popularly worn in the Middle East, North Africa, Punjab, Jamaica and Southwest Asia. A commonly used synonym is Pagri, the Indian word for turban.-Styles:...
. Multiple religions, both ancient and contemporary, require or advise one to allow their hair to become dreadlocks
Dreadlocks
Dreadlocks, also called locks, a ras, dreads, "rasta" or Jata , are matted coils of hair. Dreadlocks are usually intentionally formed; because of the variety of different hair textures, various methods are used to encourage the formation of locks such as backcombing...
, though people also wear them for fashion. For men, Islam, Orthodox Judaism, Orthodox Christianity, Roman Catholicism and other religious groups have at various times recommended or required the covering of the head and sections of the hair of men, and some have dictates relating to the cutting of men's facial and head hair. Some Christian sects throughout history and up to modern times have also religiously proscribed the cutting of women's hair.
See also
- HypotrichosisHypotrichosisHypotrichosis is a condition of abnormal hair patterns - predominantly loss or reduction. It occurs, most frequently, by the growth of vellus hair in areas of the body that normally produce terminal hair. Typically, the individual's hair growth is normal after birth, but shortly thereafter the hair...
, the state of having a less than normal amount of hair on the head or body - HypertrichosisHypertrichosisHypertrichosis is an abnormal amount of hair growth on the body; extensive cases of hypertrichosis have informally been called werewolf syndrome. There are two distinct types of hypertrichosis: generalized hypertrichosis, which occurs over the entire body, and localized hypertrichosis, which is...
, the state of having an excess of hair on the head or body - Natural afro-hairNatural afro-hairAfro-textured hair is a term used to refer to the natural texture of Black African hair that has not been altered by hot combs, flat irons, or chemicals ....
- Hair follicleHair follicleA hair follicle is a skin organ that produces hair. Hair production occurs in phases, including a growth phase , and cessation phase , and a rest phase . Stem cells are principally responsible for the production of hair....
- CowlickCowlickA cowlick is a section of hair that stands straight up or lies at an angle at odds with the style in which the rest of an individual's hair is worn. Cowlicks appear when the growth direction of the hair forms a spiral pattern. The term "cowlick" originates from the domestic bovine's habit of...
External links
- Discussion about shaving and cultures
- Answers to several questions related to hair from curious kids
- How to measure the diameter of your own hair using a laser pointer
- Instant insight outlining the chemistry of hair from the Royal Society of ChemistryRoyal Society of ChemistryThe Royal Society of Chemistry is a learned society in the United Kingdom with the goal of "advancing the chemical sciences." It was formed in 1980 from the merger of the Chemical Society, the Royal Institute of Chemistry, the Faraday Society and the Society for Analytical Chemistry with a new...