Growing and removing

Hairstyle can be an indicator of group membership:. Metalheads can often feature long hair for headbanging, although long hair is commonplace for many men and women outside of heavy metal (ex: Indian sadhus, the hippie subculture, etc). Beatle "mop-top" haircuts. Mohawk haircuts, often associated with punk rock and the punk subculture. Skinhead haircuts, where the head is often shaved completely bald, or "buzzed". Mullet hairstyles, which have stereotypically been portrayed as pertaining to rednecks. Deathhawk A larger, fuller, back combed version of a mohawk - popular in the gothic sub-culture, and heavily featured in deathrock and gothic rock bands in the 1980s. Undercut where the sides and back of the head are shaved short or bald, and the top hair is allowed to grow long. Common among so-called "cybergoths" and followers of Industrial and heavy electronic music scenes. This is especially true of women in these subcultures, although the undercut is accepted as a unisex hair style. Fascinator (hair style) where the hair is short at the back and long at the front and the front forms itself into a point. It is similar to a mullet in reverse (also known as a frullet) or a devil lock. Hair that is usually short with a long side fringe [American: bangs] is a cut often associated with emo music and its fan basis. It is often dyed black or vibrant and contrasting colours such as pink or blue. It is considered a unisex haircut and often appears similar to the mop-top.

In Western society, men's hair is generally kept short. This is due in part to 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. The Cromwell followers won. Hair length for men: Cavaliers and Roundheads, long hair in the 1960s, skinheads, mullets and other hairstyles, the uncut hair of Sikhs. Having bobbed hair was popular among the flappers 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. Hairy arms and legs, regional variations in hirsutism.

Social role of hair

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-hair (Mou, 2008; Fujimoto, 2008; Fujimoto, 2008b). 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. This indicates that the initial expression of this trait among modern humans occurred only after the migration of humans out of sub-Saharan Africa.

Hair has great social significance for human beings. It can grow on most areas of the human body, except on the palms of the hands and the soles of the feet (among other areas), but hair is most noticeable in 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, nose, ears, head, eyebrows, eyelashes, legs 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.Portrait of a Woman, Alessandro Allori (1535 - 1607; Uffizi Gallery): a plucked hairline gives a fashionably "noble brow"

Healthy hair indicates health and youth (important in evolutionary biology). Hair colour and texture can be a sign of ethnic ancestry. Facial hair is a sign of puberty in men. White hair is a sign of age, which can be concealed with hair dye. A well known old wives' tale often told to children claims that eating a large portion of bread crusts can make hair curly. Male pattern baldness is sign of age, which can be concealed with a toupee, hats or religious/cultural adornments. In modern times, it can be reversed in some men with minoxidil (marketed as Rogaine or Regaine) or finasteride (marketed as Propecia); see Baldness treatments. Rather than these options, many men simply shave their heads for a clean look. Males in some religious groups, for example Sikhs and Orthodox Jews, may follow certain rules regarding hair as part of their faith, e.g. never cut their hair, or shave some or all of it. Some groups, such as women in the Muslim and orthodox Jewish communities, cover their hair as part of religious observance. Hair whorls have been discovered to be associated with brain development.

Straight hair

According to the recent single origin hypothesis, anatomically modern humans (Homo sapiens) arose in East Africa approximately 200,000 years ago (Tishkoff, 1996). Anatomically modern behavior in terms of innovation in hunting instruments and artistic expression arose within the past 100,000-70,000 years in Africa. It was just after this period that modern humans began to expand their range to regions outside of (and within) this continent (Tishkoff, 1996). Among those in the group who left the African continent, some migrated to northern regions such as central and northeast Asia. It is hypothesized that, given their original sub-Saharan origin, these groups initially faced a special dilemma. Their dark African skin and 'kinky' African hair, both of which likely evolved to minimize entry of solar radiation into the body (Jablonski, 2006), were ill-suited to the weak sunlight of these regions. This is because, some time during the period in which humanity was in Africa, their skin had developed the ability to manufacture vitamin D (which was essential for bone development) upon exposure to UV light (Jablonski, 2006). However the UV light of northern regions was too weak to penetrate the highly pigmented skin of the initial migrants in order to provide enough vitamin D for healthy bone development (Jablonski, 2006). Malformed bones in the pelvic area were especially deadly for women in that they interfered with the successful delivery of babies; possibly leading to the death of both the mother and the infant during labor. Hence, those with lighter skin gradually survived and had children at higher rates because their skin allowed more UV light for the production of vitamin D (Jablonski, 2006).

Hence, it is probable that, during the transition period from dark to light skin, the need for vitamin D grew so intense that northerners with mutations for straight hair survived and had children at higher rates. This is likely because straight fibers better facilitate the passage of UV light into the body compared to 'kinky' hair. This, again, is in accord with 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.

Tightly coiled hair

Jablonski (2006) agrees that it was evolutionarily advantageous for pre-humans (Homo erectus) to retain the hair on their heads in order to protect the skin there as they walked upright in the intense African (equatorial) UV light (Jablonski, 2006). In addition, axilliary hair (in the underarms) was likely retained as a sign of sexual maturity. During the process of going from fur to naked skin, hair texture putatively changed gradually from straight (the condition of most mammals, including humanity's closest cousins--chimpanzees), to Afro-like or 'kinky' (i.e. tightly coiled). This is supported by Iyengar's (1998) findings that the roots of straight human hair may act as fiber optic tubes that allow UV light to pass into the skin, while it is notable that 'kinks' in fiber optic tubes are known to prevent UV light from passing through. In this sense, during the period in which humans were gradually losing their straight body hair and thereby exposing the pale skin underneath their fur to the sun, straight hair would have been an evolutionary liability. Hence, tightly coiled or 'kinky' natural afro-hair may have evolved to prevent the entry of UV light into the body during the gradual transition period towards the evolution of dark skin.

Evolutionary variation

Another theory for the thin body hair on humans proposes that Fisherian runaway sexual selection played a role. (as well as in the selection of long head hair). Possibly this occurred in conjunction during fetal/early child development neoteny such that more juvenile appearing females being selected by males as more desirable (see types of hair and vellus hair) (however, this conclusion may be more of a reflection of current standards of beauty rather than prehistoric ones).

The aquatic ape hypothesis posits that sparsity of hair is an adaptation to an aquatic environment, but it has little support amongst scientists. Humans, like all primates, are part of a trend toward sparser hair in larger animals; the density of human hair follicles on the skin is actually about what one would expect for an animal of equivalent size. The outstanding question is why so much of human hair is short, underpigmented vellus hair, rather than terminal hair.

Evolutionary biologists suggest that the genus Homo arose in East Africa approximately 2.5 million years ago (Jablonski, 2006). During this time new hunting techniques were innovated (Jablonski, 2006). The higher protein diet led to the evolution of larger body and brain sizes (Jablonski, 2006). Jablonski (2006) 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 developed the ability to sweat and thus lost body hair to facilitate this process (Jablonski, 2006). Notably, Pagel et al. (2003) argue against this hypothesis, stating that hominids without fur would not have been able to warm themselves as efficiently at night, nor protect themselves well enough from the sun during the day. However, it is likely that increased intelligence, combined with sophisticated hunting techniques, enabled humans to warm themselves at night using animal skins. Furthermore, assuming that hair loss evolved gradually, dark skin color likely developed to protect the skin during the day (Rogers et al. 2004). Hence the former hypothesis concerning loss of hair via the evolution of sweat glands is still quite viable.

Evolution of hair

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 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, humans have been hairless at least since that time.

The Savanna Theory suggests that nature selected humans for shorter and thinner body hair as part of a set of adaptations to the warm plains of the African savanna (in addition to bipedal locomotion and an upright posture). Some hold that there are several problems with this theory (including balding), not least of which is that cursorial hunting is used by other animals that do not show any thinning of hair. Nevertheless, other species likely migrated to Africa by way of a gradual process. This provided them with time to adjust to the intense UV and sunlight by way of other means (such as panting). Hominids, on the other hand, originally possessed fur, but, due to a relatively sudden change in behavior 2.5 million years ago (due to hominid inventiveness/technological innovation) that involved intense hunting during the day, they developed sweat glands that enabled them to perspire. This change necessitated the loss of most body hair in order to facilitate sweat evaporation (i.e. cool the body). Furthermore, balding usually occurs at around 30 - 40 years of age. In prehistoric times, most individuals did not live past 30.[dubious – discuss] Hence it wasn't a common trait. Also, dark pigmentation of the skin could have compensated for premature baldness (although such a condition would have still been somewhat uncomfortable relative to having hair[dubious – discuss]). Finally, there are indeed other African mammals that have lost fur due to equatorial heat. These include the African (and Indian) elephant, as well as the hippopotamus. Thus this theory remains the best explanation of human hair loss despite the persistence of those advocating the lice hypothesis et al.

Hair Analysis

In recent years, a University of Toronto laboratory pioneered the use of neonatal hair to show exposure to drugs of abuse in pregnancy. Drugs such as cocaine, methamphetamine, heroin, etc., accumulate in the neonatal hair during its growth and thus serve as a long term “memory” of what happened during fetal life. The hair analysis method used by Dr. G. Koren's research group revolutionized the diagnosis of in utero exposure to drugs. A recent study by scientists from Medical University of Vienna 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 keratin . In chickens and lizards, the keratin produced was found in their claws, but in mammals it was used to produce hair. The scientists involved were still searching for the mechanisms that allowed mammals to use the keratins of animal claws to produce hair

The soft, fine hair found on many nonhuman mammals is typically called fur.

Historically, some ideas have been advanced to explain the small amount of body hair in humans, as compared to other species. However, recent research on the evolution of lice suggests that human ancestors lost their body hair approximately 3.3 million years ago. Most mammals have light skin that is covered by fur, and biologists believe that human ancestors started out this way also. Dark skin probably evolved after humans lost their body fur, because the naked skin was vulnerable to harsh African UV radiation. Therefore, evidence of when human skin darkened has been used to date the loss of human body hair, assuming that the dark skin would not have been needed until after the fur was gone.