Scalp hair also has had some history as an organ of height display, most obviously among gorillas. But the evolution of scalp hair in human beings is more complex. There are three outstanding features of scalp hair that I will try to account for: its color, its texture, and its absence - balding.
Is it really true that gentlemen prefer blonds? Our ancestral scalp hair color was black, with brown variants in many sub-groups, judging from related primates and the general distribution of human hair color throughout the world. Among human sub-groups having shades of brown adult scalp hair, there is almost invariably an increase in pigmentation with age. Most people recognize that just because you have a towheaded child, it doesn't at all mean he'll be blond as an adult. In a community with a number of brown-haired adults, there will be a statistical association of hair color with age groups, similar to the correlation of size with age. Like a short adult, a blond adult will carry some subordinate signal element.
Apparently, blond adults are a comparatively recent human innovation, and they originally came from a relatively small part of the world. Human beings appear to be at the same stage of blond-brunette evolution as the gibbon Hylobates lar lar; having come from a dark haired ancestral stock, we have substantial hair color variation, within which there are opposing sexual preferences. (Just flip through the magazine ads and see how infrequently a blond man is shown with a dark-haired woman) Yet we haven't reached the sexual stage (represented by the species H. concolor) of all blond females and all dark-haired males. In one human subspecies (the Australian aboriginals) there is a striking age gradient in hair color throughout the entire population. The young are dark of skin and eyes but have exceptionally blond hair. This darkens with age until it is black or a very dark brown.
We can separate movie sex-goddesses into two types: the baby faced sort and the dominant kind. Generally, the baby face neotenics (childlikes) have blond hair which, of course, complements the signal. Women, in cultures where it is accepted, are fond of bleaching their hair. Like thin-arched eyebrows and "made-up" eyes, blond hair gives them a childlike air, that is, the social posture of an attractive subordinate.
It is no news to anybody that scalp hair affects social posture. Millions upon millions of dollars and man-hours are spent annually modifying scalp hair so that people can present a better social face. Culture-specific alterations and whims of style tend to obscure some rather fundamental themes permeating our values about scalp hair. In fact, when examined carefully, the cultural modifications support to a great degree the natural signals already present.
The actors of ancient Greece used a black wig for the villain, blond for the hero, and red for the clown or fool. According to Kathrin Perutz, "light hair is usually the wife, heroine, princess, maiden in distress or Doris Day, dark hair is for women, mistresses, or more aggressive heroines." For example, Salome is always pictured with tendrils black and tightly curled, not too dissimilar from pubic hair. Yeats saw the special attraction of a blond beauty:
Never shall a young man
Thrown into despair
By those great honey-colored
Ramparts at your ear
Love you for yourself alone
And not your yellow hair.
In order to investigate the biology of scalp hair patterns, other than color, we have first to take a brief look at other primates. From the extreme use of facial hair as an enlarged fan around the face, such as is found in the saki monkey, Goeldi's marmoset, and the crab-eating monkey, there is a complete spectrum of specializations into dorsal crests, brow bands, cheek whiskers, and chin whiskers. The moor macaque and the drill are two species that have all, or most, of these specializations. It is difficult not to argue that the scalp hair functions mainly as an organ of intimidation in primates. The head hair on the gorilla forms a prominent crest along the center line from front to back. The crest is erected, when the animal is threatening, by pulling the skin down in a forward direction over the scalp.
Scalp hair doesn't seem to be a protective "hat." The thickness or length of the hair on the head doesn't seem to be related to the amount of time spent out in the sun. Baboons living in semi-open situations have short hair on top of the head while some monkeys living in dense forests have a thin mat of scalp hair.
There are a number of scalp hair patterns in primates. Some have hair fans, like open taxicab doors, with a part in the middle, giving the head an appearance of greater breadth (e.g., the golden marmoset). More commonly, the head hair is arranged as a middle crest. Many have crests of different color from the rest of the head hair. The macaques, gelada baboon and the drills have dark crests on light backgrounds, while Geoffrey's marmoset has a white crest on a darker background.
There are some sexual differences in scalp hair among the primates (the males generally have more) but not as many as in the case of the beard. If the primate scalp hair has functioned only as a threat device, then one could expect more scalp hair among males. But humans and a few other primate species do not fit this pattern; some men have almost no scalp hair at all.
Among human beings, and a few other primate species, it is the female who has the full head of luxuriant hair. Men's hair tends only to be somewhat bushier, in some Caucasian groups. Human females often repudiate their attractive femininity by cutting back their hair near the stylish male length (for example, suffragettes, flappers, lesbians, high-powered businesswomen, nuns and Orthodox Jewish brides).
Do our scalp patterns reflect an overall primate trend? First, we are kind of similar to the other primates in having a poor correlation of hair thickness and length with different climates. For example, the African Hottentots and Bushmen occupy one of the sunniest places on earth, yet the hair is arranged in little peppercorn tufts scattered over the scalp, exposing the naked skin in between, much like the very young of more northern African tribes. So one might begin to suspect that human scalp hair may also function as a social organ - as per primate tradition.
Our balding isn't peculiar to ourselves. It is found in several primate groups - apparently having evolved independently in all of them. South American uakari monkey balds with age even more completely than human beings. Male uakaris generally become more bald than females. Among the African monkeys the stump-tailed macaque males bald with age. Among the apes both the chimps and orangs experience balding, but the trait is highly variable among chimps - occurring more notably with age and more so among males than females.
Balding is not a uniquely human phenomenon. Several other species of primates also bald and, as in humans, it is more common in adult males than among females or the young. Shown above are the Chimp, Man, Uakari monkey, Stump-tailed macaque, and the Orang.
Because of our particular attitudes toward aging we are accustomed to think of balding as a deterioration process - a symbol of senility, a byproduct of a general decline. Interestingly enough, this attitude prevails even among physicians, gerontologists, and physical anthropologists. In a culture that worships youth as ours does, it probably couldn't be otherwise, but there is more to balding than being a symptom of senescence. Among those other balding primates it seems to be a social badge of privilege, that is, an organic symbol of status. Its evolutionary history among human beings once followed this same pattern and became even more exaggerated.
But how can we reconcile these two divergent primate patterns: some species using a thick mat of erectile scalp hair, and others a bared skin, all for a similar signal? I think there are several lines of evidence pointing to a plausible answer.
Prosimians - the early primates - and virtually all living primates are without foreheads. The brow is the highest point that you see when the animal is facing you. The main avenue available to expand the apparent size of the face is to top the brow or scalp with a crest of erectile hairs. Among apes this is especially apparent in the gorilla. Old males have a long erectile scalp crest, which adds several inches to their stature.
One of the general trends among primates, however, has been to remove the hair from the face. A naked face amid head hair attracts attention and greatly facilitates communication by allowing for skin color changes and obvious skin wrinkling, which are at least hampered by the hairy covering. Changes in the skull which expand the braincase or lower the brow ridge to form a forehead offer a new surface for skin exposure.
Among the species with well developed foreheads, there has been a switch from the use of hair to the use of skin. As has so often been the case when one threat device is substituted through evolution for another, the old device becomes a symbol of femininity or pre-adolescence, a symbol of those of low social stature. I think this has happened to human scalp hair (as well as uakari monkey scalp hair).
Why exactly should the forehead and scalp be bared in threat? Again, the other bald primates provide some interesting insight into our own balding process. Skin color is of utmost importance in uakari monkey communication. The entire face turns brilliant crimson as the skin is distended with blood when a monkey is threatening. Somewhat the same thing is true with the stump-tailed macaque. Like the uakari monkey, mature macaque males have a network of large, sponge like, cavernous vessels just under the surface of the skin on the forehead and scalp, that can be flooded with blood under the stimulus of certain emotions.
The forehead also displays skin texture. As males of all primate species tend to have coarser hair than the females, among many of them the exposed skin areas become more granular, pitted, and irregular with age. In the forehead area, texture seems to be an important part of the display. An old male macaque monkey has a particularly greasy dome. The stump tailed macaque monkey has a well-developed sebaceous (oil) gland system on the same areas of the face and the forepart of the scalp as man does. In this species there are sexual differences in this character, suggesting that the organ has other functions than keeping the skin from drying out. Secretions from this gland are more abundant at puberty in human males than females, and remain so throughout life. The human forehead, scalp, and face become quite greasy if these oily products are left to accumulate.
Like the uakari monkey, humans redden with age or anger, and the function appears to be primarily a social signal. Facial reddening does in fact carry important information and serves no other physiological function. As the blood vessels of the face flush, the skin reddens, the angular vein which runs upward from the bridge of the nose is especially distended and has been referred to as the temper or anger vein.
Exposed foreheads accomplish several things. (1) They increase the area for color and skin position displays; (2) they increase the apparent area of the face; and (3) they magnify the changes in skin texture with age.
But there is a fourth function that is perhaps the major explanation for human balding. There are two fundamental, instinctive things every baby primate must know. It must be able, from almost the very beginning, to hold tightly to the hair of its usually arboreal mother, and it must be able to nurse. Some where in that complicated inborn neural switchboard, these two circuit have not been kept completely separate.
Terence Anthoney's work on the development of adult sexual behavior and grooming, starting from the babies' nursing and hair fondling in baboons, has told us a lot about ourselves and our attitudes toward hair. When the young are weaned they still retreat to the security of hair fondling. Growing out of these associations, hair grooming later in life takes on an important role as a socio-sexual gesture. Thus baboon hair is not only an organ to regulate body temperature and to threaten with, it is something to be loved.
Human babies are like baboons in this respect: they like to run their fingers through their mother's hair when they nurse. But our human nakedness leaves little hair to fondle. Babies cannot easily fondle crotch or axillary hair, and women have very little facial hair. All that remains is scalp hair. Developmentally, this is where humans get their love for hair - not all hair, just scalp hair. We associate it with sex and tenderness. It is denser, finer, and longer in females.
If mothers have very short hair or if babies are nursing from bottles their little hands reach up to their own heads, coiling and twining their own hair. More commonly, they substitute a soft "velum" blanket for the missing maternal hair. Even well after weaning, some use a nipple substitute - the thumb - and fondle their mother's or father's hair when the are tired or insecure. A puzzled or frustrated man uses the same gesture in a scalp hair stroke or moustache pat, not to displace his anxiety, but to re treat in a subtle way to the security of an earlier age. Baboons and humans alike are conditioned early in life (and perhaps with some genetic guidance to love scalp hair.
Indirectly because of our nakedness, scalp hair has changed its sign role. No longer is it a coarse erectile crest used to signal threat. Its role has shifted from an emphasis on male dominance to an organ of child-female interaction. And as an extension of the latter, it has become part of the allure of female attraction.
What has this done for the male scalp? It has reversed the selection pressures for status opposite to long tresses - a bald head. One identifies a full head of hair with femininity and youth. The actors who are chosen to play the roles of very young men in movies or on television frequently have an unusually low hairline, so that the forehead is reduced to a narrow band of skin. This is also true of the "baby-doll" actresses. People with this kind of hairline look younger than their age.
The status signal of the high forehead is obscured by our current accent on youth. Head shaving is a common phenomenon among many tribes and often is done only by males. Interestingly enough, it is sometimes performed in a manner which exaggerates the natural balding patterns. For example, the South American Yanomano shave the crown of the head, leaving a wreath of hair. Scars from battle are exhibited in this manner. Another South American tribe, the Tchikrin, pluck all facial hair, even in small children. The men, especially, have their hair plucked back from the forehead to the crown or hair whorl area. It was a common practice during the 1800's for Chinese males to shave the forehead well back to the top of the head and then braid the remaining hair in a queue.
At the present time Western cultures are caught in a pinch between the adulation of youth - which is responsible for our holding low hairlines in esteem - and our continuing respect for status and the high forehead which retains an element of nobility or at least an aristocratic man. The superhero males of the comics almost invariably have a high hairline.
The most common type of pattern balding is for two naked arches to expand upward from the brow, leaving a strip of hair along the midline. Even on non-balding foreheads, these lines sometimes come together to form a sharp "widow's peak." This pattern presumably arose from an upward movement of the double-crescent hairline which rims the brows of the other primates. These double arches baring the upper temples seem to carry a signal of stature even when diluted into a double scallop hairline, non-balding pattern, such as is found in women. The straight line pattern has a more juvenile character to it.
Virtually every human sub-group has some form of pattern balding, but there are extreme variations in onset, rate, and patterning. Some combine the bald spot with the double arch, and others, especially in the Eastern Mediterranean area, have a line-of-march which moves backward across the head with age. Similar patterns are seen in other primate species. Some macaques, chimps, and some baboons seem to expand the balding zone backward along the medial line, a pattern sometimes seen in humans.
Human balding occurs in several patterns. These sometimes occur together or separately and occur at different frequencies. Some noteworthy patterns are: (A) Double point, forehead recession, widow’s peak; (B) Monk’s spot (usually A and B occur together; they are common in many European countries); (C) Line-of-march, common in the Mediterranean countries (e.g., Albert Einstein); (D) Single point forehead recession, common among Orientals (e.g., Mao Tse-tung).
In the distant past, the gloss of a bare scalp became the badge of leadership and dominance, whether it was the greased plucked head of the Yanamano or the oily, scraped scalp of an Ainu, Jew, Chinese, or Saxon. It is mimicked unconsciously by shiny metal helmets in many cultures.
Why then do we have so many hangups about baldness? Probably more people have been duped by "hair-growing" elixirs than by any other ineffectual cosmetic. Any man's magazine on the newsstand contains advertisements for secret formulas and special treatments to bring back lost scalp hair. Hairpieces and wigs are commonly used by men to cover the bald patches and receding hairlines. One of the newer alternatives, made possible by plastic surgery, is the grafting of small pieces of hair from other parts o the scalp onto thinning areas, to recreate permanently one's earlier hairline. Recreating the hairline of a 20-year-old is a retreat to the courtship age. We live in a society which bases most status evaluation on one's potential courting currency; that is the secret behind our reverence for youth.
The evolution of human scalp hair has followed this pattern: first it was an erectile threat crest, then strangely, it began to shift. Balding became the threat ideal, and a full head of soft hair was what we clung to as babies - a symbol of maternal-sexual security and attraction, like a round, warm breast. But recently the evolutionary bent has looped into an even odder twist. The symbols of age and status are in disfavor, even repugnant. Now it is the mature male who mimics the post-puberty vigor of youth that has become our and man's ideal. More than any of the other organic epaulets of the past, the threat value of the very high forehead and its exaggeration the bald scalp, has been debased. And like the Confederate dollar, there is something uncomfortably humorous about its continued existence.