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Z-patterned tightly coiled, sharply angled 4c Mostly Z-patterned tightly kinked, less definition Strands F Fine Thin strands that sometimes are almost translucent when held up to the light. Shed strands can be hard to see even against a contrasting background; similar to hair found on many people of Scandinavian descent. You can also try rolling a strand between your thumb and index finger. Fine hair is difficult to feel or it feels like an ultra-fine strand of silk. M Medium Strands are neither fine nor coarse; similar to hair found on many Caucasians. Medium hair feels like a cotton thread. You can feel it, but it isn't stiff or rough. It is neither fine nor coarse. C Coarse Thick strands whose shed strands usually are easily identified against most backgrounds; similar to hair found on many people of Asian or Native American descent. Coarse hair feels hard and wiry. As you roll it back and forth, you may hear it. Volume by circumference of full-hair ponytail i circumference less than 2 inches 5 centimetres ii 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. Warmth Polar bears use their fur for warmth and while their skin is black, their transparent fur appears white and provides camouflage while hunting and serves as protection by hiding cubs in the snow. While humans have developed clothing and other means of keeping warm, the hair found on the head serves primarily as a source of heat insulation 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' 'rising up' , but is more commonly known as 'having goose bumps ' in English. The opposite actions occur when the body is too warm; the arrector muscles make the hair lie flat on the skin which allows heat to leave. Protection In some mammals, such as hedgehogs and porcupines , the hairs have been modified into hard spines or quills. These are covered with thick plates of keratin and serve as protection against predators. Thick hair such as that of the lion's mane and grizzly bear's fur do offer some protection from physical damages such as bites and scratches. Touch sense Displacement and vibration of hair shafts are detected by hair follicle nerve receptors and nerve receptors within the skin. Hairs can sense movements of air as well as touch by physical objects and they provide sensory awareness of the presence of ectoparasites. The eyebrows provide moderate protection to the eyes from dirt , sweat and rain. They also play a key role in non-verbal communication by displaying emotions such as sadness, anger, surprise and excitement. 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. Evolution Hair has its origins in the common ancestor of mammals, the synapsids , about million years ago. It is currently unknown at what stage the synapsids acquired mammalian characteristics such as body hair and mammary glands , as the fossils only rarely provide direct evidence for soft tissues. Skin impression of the belly and lower tail of a pelycosaur , possibly Haptodus shows the basal synapsid stock bore transverse rows of rectangular scutes , similar to those of a modern crocodile. The oldest undisputed known fossils showing unambiguous imprints of hair are the Callovian late middle Jurassic Castorocauda and several contemporary haramiyidans , both near-mammal cynodonts. Some modern mammals have a special gland in front of each orbit used to preen the fur, called the harderian gland. Imprints of this structure are found in the skull of the small early mammals like Morganucodon , but not in their cynodont ancestors like Thrinaxodon. Fur could have evolved from sensory hair whiskers. The signals from this sensory apparatus is interpreted in the neocortex , a chapter of the brain that expanded markedly in animals like Morganucodon and Hadrocodium. A full pelage likely did not evolve until the therapsid-mammal transition. In varying degrees most mammals have some skin areas without natural hair. On the human body, glabrous skin is found on the ventral portion of the fingers , palms , soles of feet and lips , which are all parts of the body most closely associated with interacting with the world around us,  as are the labia minora and glans penis. Pacinian corpuscles , Meissner's corpuscles , Merkel's discs , and Ruffini corpuscles. The Naked mole-rat Heterocephalus glaber has evolved skin lacking in general, pelagic hair covering, yet has retained long, very sparsely scattered tactile hairs over its body. Relevant discussion may be found on the talk page. November Learn how and when to remove this template message The general hairlessness of humans in comparison to related species may be due to loss of functionality in the pseudogene KRTHAP1 which helps produce keratin in the human lineage about , years ago. Humans are the only primate species that have undergone significant hair loss and of the approximately extant species of mammal, only a handful are effectively hairless. This list includes elephants, rhinoceroses, hippopotamuses, walruses, some species of pigs , whales and other cetaceans , and naked mole rats. Dark skin probably evolved after humans lost their body fur, because the naked skin was vulnerable to the strong UV radiation as explained in the Out of Africa hypothesis. Therefore, evidence of the time 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. It was expected that dating the split of the ancestral human louse into two species, the head louse and the pubic louse , would date the loss of body hair in human ancestors. However, it turned out that the human pubic louse does not descend from the ancestral human louse, but from the gorilla louse , diverging 3. This suggests that humans had lost body hair but retained head hair and developed thick pubic hair prior to this date, were living in or close to the forest where gorillas lived, and acquired pubic lice from butchering gorillas or sleeping in their nests. 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 arrector pili muscles relax, preventing heat from being trapped by a layer of still air between the hairs, and increasing heat loss by convection. 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. 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, and not all human populations today have sexual dimorphism in body hair. A further hypothesis is that human hair was reduced in response to ectoparasites. When our ancestors adopted group-dwelling social arrangements roughly 1. Early humans became the only one of the primate species to have fleas , 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. Giles also connects romantic love to hairlessness. As a result, humans evolved the ability to sweat: The female-male size differential among other closely associated primates is much greater than among humans, and therefore it was reduced during human 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. However, while men develop longer, coarser, thicker, and darker terminal hair through sexual differentiation , women do not, leaving their vellus hair visible. Texture Curly hair Yellow curly hair and scalp from body which had long black wig over hair. Parts of wig plait remains. From Egypt, Gurob, probably tomb Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. August Learn how and when to remove this template message Jablonski  asserts head hair was evolutionarily advantageous for pre-humans to retain because it protected 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 because 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. Sometime during the gradual process by which Homo erectus began a transition from furry skin to the naked skin expressed by Homo sapiens, hair texture putatively gradually changed from straight hair[ citation needed ] the condition of most mammals, including humanity's closest cousins—chimpanzees to Afro-textured hair or 'kinky' i. This argument assumes that curly hair better impedes the passage of UV light into the body relative to straight hair thus curly or coiled hair would be particularly advantageous for light-skinned hominids living at the equator. It is substantiated by Iyengar's findings that UV light can enter into straight human hair roots and thus into the body through the skin via the hair shaft. Specifically, the results of that study suggest that this phenomenon resembles the passage of light through fiber optic tubes which do not function as effectively when kinked or sharply curved or coiled. In this sense, when hominids i. 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. However, such anthropologists as Nina Jablonski oppositely argue about this hair texture. Specifically, Jablonski's assertions  suggest that the adjective "woolly" in reference to Afro-hair is a misnomer in connoting 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 structure that in turn, Jablonski argues,  more likely facilitates an increase in the circulation of cool air onto the scalp. Further, wet Afro-hair does not stick to the neck and scalp unless totally drenched and instead tends to retain its basic springy puffiness because it less easily responds to moisture and sweat than straight hair does. In this sense, the trait may enhance comfort levels in intense equatorial climates more than 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. 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.
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