Hair
The fine, soft hair found on many nonhuman mammals is typically called fur; wool is the characteristically curly hair found on sheep and goats. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class. Although other non-mammals, especially insects, show filamentous outgrowths, these are not considered "hair" in the scientific sense.
The projections on arthropods such as insects and spiders are actually insect bristles, composed of a polysaccharide called chitin. There are varieties of cats, dogs, and mice bred to have little or no visible fur.
The hair can be divided into three parts length-wise, (1) the bulb, a swelling at the base which originates from the dermis, (2) the root, which is the hair lying beneath the skin surface, and (3) the shaft, which is the hair above the skin surface. In cross-section, there are also three parts, (1) the medulla, an area in the core which contains loose cells and airspaces (2) the cortex, which contains densely packed keratin and (3) the cuticle, which is a single layer of cells arranged like roof shingles.
Hair types
Human beings have three distinct types of hair:
Lanugo is fine hair that covers nearly the entire body of a fetus.
Unless born prematurely, the fetus loses this layer of hair before birth. Lanugo also sometimes returns in cases of malnutrition or extreme anorexia nervosa, as the starved body attempts to insulate itself.
Vellus hair is extremely short, fine, scarcely noticeable hair that covers most the human body in both sexes.
Terminal hair is fully developed hair, which is generally longer, coarser, thicker, and darker than vellus hair.
Characteristics
Balding and greying
The tendency of older people to develop grey hair is due to "a massive build up of hydrogen peroxide due to wear and tear of our hair follicles ... winds up blocking the normal synthesis of melanin, our hair's natural pigment." Grey hair is considered to be a characteristic of normal aging.
The age at which this occurs varies from person to person, but in general nearly everyone 75 years or older has grey hair, and in general men tend to become grey at younger ages than women.
It should be noted however, that grey hair in itself is not actually grey; the grey head of hair is a result of a combination of the dark and white/colourless hair forming an overall 'grey' appearance to the observer. Red hair usually doesn't turn grey with age; rather it becomes a sandy colour and afterward turns white.
Lafayette Baker, who died July 3, 1868, use of an atomic absorption spectrophotometer showed the man was killed by white arsenic. Baker's diary seems to confirm that it was indeed arsenic, as she writes of how she found some vials of it inside her brother's suitcoat one day.
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. 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
Human "nakedness"
Human hair under 200-times magnification
Transverse section of hair follicle
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.
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.
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.
These include the African (and Indian) elephant, as well as the hippopotamus. As a result, humans developed the ability to sweat and thus lost body hair to facilitate this process (Jablonski, 2006).
Hence the former hypothesis concerning loss of hair via the evolution of sweat glands is still quite viable.
Texture
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). 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.
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).
It is hypothesized that, given their original sub-Saharan origin, these groups initially faced a special dilemma. 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).
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.
The EDAR locus and the evolution of straight 'coarse' hair in East Asia
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). 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. It is similar to a mullet in reverse (also known as a frullet) or a devil lock.
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. http:query.nytimes.com/gst/fullpage.html?res=9C03E0DE1030F93AA2575BC0A9659C8B63&sec=health&spon=&pagewanted=2.
Milton's Teeth and Ovid's Umbrella: Curiouser & Curiouser Adventures in History, p.53.