The Scars of Evolution

by Elaine Morgan

  Humans still retain the capillary muscles in good working order, but their functioning is comically ineffective. Since the vestigial hairs they are attached to often fail to reach the surface of the skin, the only result achieved is goose-bumps. We produce them in cold weather with the subconscious aim of bushing out a non-existent coat of fur. When we are frightened, some primitive level of our brain may try to raise our hackles in the hope of scaring off the enemy.

  Hair or fur is a mammal’s first line of defence against abrasions – cuts and grazes, the sting of an insect, the scratch of a thorn. Perhaps partly in an attempt to replace this defence, our skin has become thicker than that of our nearest relatives, the apes. Yet at the same time human skin contains more blood vessels and is more richly endowed with nerve endings. This means that even a small lesion is liable to bleed more, and hurt more, than if we had skin like an ape’s.

  Much in the news recently is another disadvantage of nakedness – the danger to light-skinned races of over-exposure to ultra-violet light and the consequent risk of skin cancer. Most mammals do not incur this risk, except where the hair is missing. In horses, for example, a malignant melanoma may sometimes develop in the bare patch under the tail.

  Cancer is the most serious of the possible ill-effects of exposure to ultra-violet rays, but it is not the only one. Exposure to strong sunlight can damage light-coloured skin to the extent of putting the skin glands temporarily out of action. In the heyday of the British Empire, young men and women fresh out of England to serve in India found that part of the white man’s burden was susceptibility to an uncomfortable skin condition known as ‘prickly heat’.

  Since the loss of body hair, human skin has elaborated an auxiliary line of defence against the danger of ultraviolet rays. Scattered throughout the top layer of our skin are small spider-shaped cells (melanocytes) which produce a substance called melanin, after the Greek word for ‘black’. The cells respond to ultra-violet exposure by increasing the output of melanin, which is injected into the surrounding skin cells where it forms a protective shield like a minuscule sunshade over each cell membrane on the side nearest to the surface. This darkens the colour of the skin and protects it by absorbing the harmful ultraviolet rays. In the dark-skinned races the protective shield is permanent.

  There is some melanin in the skin of apes and monkeys, but its purpose there is more obscure. It is hardly needed as a protection against the sun, for most of these animals live in shady places, and all of them have bodies which are covered with hair. Since their skin colour thus cannot affect their chances of survival, it is not governed by the influence of natural selection, and varies widely between species, and sometimes between individuals. The Celebes ape is born with a black skin which later turns white. The rhesus monkey’s skin is pinkish with random splotches of blue. There may be dark-skinned and light-skinned individuals within a single troop of chimpanzees.

  In the days when Theology was queen of the sciences, learned men were as curious about their progenitors as we are today. One of the questions they asked themselves was: ‘What colour was Adam?’ Considering in whose image Adam was created, it was a matter of some delicacy, never satisfactorily resolved. The old monks who had the job of illuminating Holy Writ ignored the issue, and went on drawing little pictures of a white Eve with a white Adam.

  Some of the early evolutionists thought they had cracked the problem. Since they could now dispense with Adam, they felt able to jettison the egalitarian Biblical doctrine that all men were brothers: they suggested that the races had always been separate, having evolved independently from the beginning. Behind that hypothesis we seem to detect an unspoken conviction that some of us are obviously descended from a rather better class of ape than others.

  We now know that all races share a common ancestry, and there is every reason to believe that our earliest common ancestors lived in Africa, where protection against ultra-violet rays would be at a premium.

  This conclusion has been challenged. It is argued that protective pigment could not have evolved by natural selection because the danger it protects against does not usually manifest itself until middle age, when child-bearing is over; therefore, a female who was not protected against skin cancer would produce just as many offspring as a protected one, and her genes would not be selected out. This argument is unsound. Half our genes come from our fathers, and a man’s reproductive capacity does not close down as early as a woman’s. He can certainly increase the number of his descendants by avoiding late-onset disease and living longer, so that over time natural selection in an African climate would favour dark skin.

  Besides, the white races bear the evidence of ancestral pigmentation in their own skins. All human beings, of whatever race, have the same number of melanocytes. In northern races they are largely surplus to requirements and remain relatively inactive because in temperate climes the ultra-violet rays are seldom strong enough to be dangerous. But they are still there, presumably a relic of our heritage.

  So the question of racial differences in skin colour does not revolve around the question of why some human populations became black, but why some later faded to lighter shades. The best available theory is that it happened when they migrated from Africa to northern latitudes where the climate was cooler and cloudier and where the food was scarce in winter.

  They were then in less danger from strong sunlight and in more danger from lack of vitamin D. A shortage of this vitamin in the diet does not matter too much in hot countries. Cells in the skin can manufacture their own supply, but they cannot do it – any more than a leaf can manufacture chlorophyll – in the absence of sunlight. The best survivors in northern countries would be the ones with the least active melanocytes (that is, the palest skin) because the limited available sunlight could soak into their skin more easily and help to make vitamin D.

  So it could be claimed that in the end natural selection did a good job, under difficult circumstances, both for the dark races and the pale ones. As a method of counteracting part of the ill-effects of hair loss, it was indeed a neat piece of damage limitation. The drawback is that it takes a very long time for a human population to evolve the kind of skin colour fitted to a particular latitude. The system is foolproof only as long as people stay put. Nowadays they do not stay put, and sometimes they suffer from it.

  For example, when Asian women settle in Britain and continue to live on the same diet that kept them healthy in India, they are sometimes found to be suffering from rickets. A tropical sun is strong enough to penetrate through a thin sari and enable their skin to make vitamin D, but the British climate leaves them deficient in it.

  The reverse move – from the temperate zones to tropical ones – can be even more damaging. People of European origin have made their homes in all parts of the world and the possible ill-effects have only recently been fully appreciated.

  There has been a startling increase in the frequency with which malignant melanoma occurs throughout the Western world, with a doubling of the frequency of the disease each decade since records started. The rise has been highest among white populations living in hot countries. People with fair skin and red hair seem to be especially vulnerable.

  It is very rare in dark-skinned people, and the incidence among the whites seems to vary with the distance from the equator. It is high in places like Arizona, Israel, Hawaii and Australia. In New South Wales it accounts for seven per cent of all cancers, as compared with one per cent in the United Kingdom. There are now fears that damage to the ozone layer could accelerate the increase.

  ‘Naked as Nature intended’ was a persuasive slogan of the early Naturist movement. But Nature’s original intention was that the skin of all primates should be unnaked. Faced with the phenomenon of the bald-bodied ape, she has tried various experiments without finding a universal solution.

  Doctors have tried hard to publicise the fact that exposure to the sun is possibly dangerous, and in the long run anti-cosmetic – it is the direct cause of
the wrinkles associated with ageing and the broken veins which sometimes appear under the skin. But their campaign has had only limited success. In an American survey, over 50 per cent of those questioned knew that there was a link between sun-bathing and cancer, but two-thirds of that number continued to sun-bathe, and in most cases without using a barrier cream. Westerners cling to their belief that a tanned skin is ‘healthier’ than a pale one, and to the even more insidious idea inculcated by Coco Chanel that a tanned skin should be regarded as fashionable, and sexy, and a status symbol.

  Some of the physical left-overs from a previous hairier existence remain with us (like the goose pimples), doing neither good nor harm, and in the long run will probably disappear. A more mysterious phenomenon is that of the sebaceous glands which cause anguish to so many adolescents by being the cause of greasy skin and acne.

  The oiliness comes from a fatty substance called sebum. The sebaceous glands which secrete it are an appendage of the hair follicles, and the sebum seeps out onto the hair shaft and helps to keep the fur of mammals sleek and waterproof. A. M. Kligman, who made a special study of the subject, wrote:

  The original purpose was not so much to protect the skin as the hair. In man, however, save for a few specialised regions, hair is a vestigial and rudimentary feature. With hair rendered obsolete, the sebaceous gland is literally out of work. It is a living fossil with a past but no future.

  So it would be reasonable to expect that in man the glands would have dwindled to mere vestiges, just as over most of our bodies the hairs themselves have dwindled.

  Instead of that, these oil glands have run riot. In our nearest relatives, the African apes, some sebaceous glands are found scattered over the body, but they are few and small. In man they are numerous and relatively enormous, especially on the face and scalp, sometimes extending to the neck and to regions of the upper part of the body.

  An American enquiry into ‘What good is human sebum?’ reported that the short answer was ‘No good’. It is not needed to keep the skin moist and supple: the softest human skin is that of a child, yet the sebaceous glands do not begin to operate until puberty. It used to be thought that the sebum probably helped to kill bacteria which landed on the skin, but that proved to be a fallacy. Yet from adolescence onwards our skin goes on producing sebum, not in response to any environmental stimulus (as is the case with sweat) but at a constant rate.

  Globules of fat emerge from the sebaceous glands onto the surface of the skin, mingled with dead and decaying fragments of cells. The mixture is toxic to living tissue. At puberty the glands are growing so rapidly in the so-called ‘acne areas’ (face, chest and back of the torso) that the well of the hair follicle may become filled with a plug of sebum and cell débris. Or a cyst may be formed in which trapped bacilli produce irritant fatty acids and cause inflammation. The clinical symptoms – pimples, blackheads and inflamed nodules – are found most often on the face, but may extend to all the acne areas. On the scalp, where the follicles are less likely to become blocked, the same generous effusion of sebum provides a breeding ground for either dandruff or seborrheic dermatitis, and sometimes both.

  This unmerited disaster may be visited on young people of either sex, but there are more victims among young males because males have larger sebaceous glands. The size of the sebaceous glands is influenced by the sex hormones (castrated males do not suffer from acne), and attempting to tinker with the balance of these hormones can have side-effects more dismaying than the pimples.

  The effects may be partly mitigated by the use of antibiotics, but the only permanent cure is to grow older. With the passage of time the skin gradually adjusts to the situation, and the sebum is able to make its exit to the surface without battling its way out. After that the cosmetic results are less noticeable. Often they are confined to what the face powder advertisements used to denounce as ‘shiny nose’.

  It is cold comfort to a fifteen-year-old to know that the condition will not last, or to reflect that no other species in the animal kingdom has to put up with it. William Montagna, leading specialist on primate skin, commented: ‘The human body appears to contain senseless appendages and even to make mistakes, but the sebaceous glands are too numerous and too active to be described as trivial.’

  Other equally unexpected features of human skin remain to be discussed, but one thing should already be clear: a mammal cannot shed its coat of fur as a man can shed a suit of clothes and leave everything else unchanged. It is as revolutionary a change in life strategy as walking on two legs, and as far-reaching in its secondary effects. These complex changes would not have evolved, in our species alone, without some compelling reason.

  6

  Explaining Hairlessness

  ‘In the water, fur provides poor insulation and becomes atrophied.’

  V. E. Sokolov: Mammal Skin

  In 1989, before embarking on this chapter, I walked into an Oxford bookstore to find out what the students in that great seat of learning were being taught about this subject. I was offered, and purchased, the latest editions of two textbooks – both comprehensive, highly commended and frequently updated to keep pace with the latest scientific discoveries. One was called Introduction to Physical Anthropology and the other Physical Anthropology.

  One of them devoted three words to the topic. By comparison with the apes, it conceded, humans ‘have less hair’. The other volume was more reticent and avoided any mention of the subject whatsoever.

  The writers are not falling down on the job. Their sole object is to help students to pass examinations. They know that the question of why Homo is hairless will not crop up in the examinations, because neither the people who set the papers nor the people who mark them know what the answer is.

  While that seems a little bit like a conspiracy of silence, it is at least more dignified than the strategy in use some twenty years ago. At that time the question was regularly countered by a flat denial. Experts explained that people who imagined humans had lost their body hair were being misled by a kind of optical illusion, because in fact humans have as many hair follicles all over their bodies as chimpanzees do – at least as many, possibly more. The fact that the hairs happen to be shorter, in some cases so short that they do not emerge above the surface of the skin, was dismissed merely as a ‘quantitative difference’ not requiring explanation.

  This kind of evasion was an insult to the meanest intelligence, yet it was regularly uttered by professors and parroted by undergraduates. Desmond Morris copied down verbatim the pronouncement of one famous authority during a television programme: ‘The assertion that we are the least hairy of all the primates is, therefore, very far from being true; and the numerous quaint theories that have been put forward to account for the imagined loss of hair are, mercifully, not needed.’

  On television there has only once been anything approaching a debate on the aquatic theory. It took place in Chicago in 1972, and in the course of it a professor of anthropology was asked why man had less hair than the apes. Unprepared for the question, he earnestly assured viewers that there was no mystery about it: the answer had been found – the matter was well understood – the solution was there, on record, somewhere in the literature – but unfortunately it had slipped his mind.

  For the benefit of any who might find themselves in a similar predicament, this chapter lists the explanations that have appeared ‘in the literature’. Human nakedness has been attributed at various times to (1) ticks, (2) sex, (3) hunting, (4) neoteny, (5) noonday foraging, (6) allometry and (7) water. It will be for the reader to decide which of them is least implausible.

  1 The parasite argument was advanced by a man called Belt, who argued that a naked primate would be less liable to harbour ticks and other noxious parasites which in the tropics may constitute a serious danger to health. Darwin discussed this idea and dismissed it on the grounds that many quadrupeds are faced with the same problem but none have resorted to such a drastic measure of gaining relief. As an anti-parasi
te device nakedness would not only have been drastic, it would also have been ineffective. The flea that feeds on man is an exclusive species, recognisably different from all others, indicating that it has been our faithful companion over millions of years, and our lack of fur has failed to deter it.

  2 Sex was Darwin’s theory. His second book on the evolutionary theme was entitled The Descent of Man and Selection in Relation to Sex. He had not abandoned his belief that hairlessness constituted ‘an inconvenience and possibly an injury’, but he had collected evidence that many species had evolved features which were in themselves inconvenient or injurious yet were retained because they were attractive to the opposite sex.

  Among his numerous examples were a species of lyre bird with a long, dangling tail which must hamper it in moving through the trees, and various brightly coloured male fish and birds whose adornment would make them more conspicuous to predators. These characteristics were nevertheless passed on because in those species the sexual adornment enabled the most spectacular males to attract more females and therefore to leave more descendants than their drabber rivals.

  However, human hairlessness fails to fit into the normal pattern of sexual selection in several important respects. Firstly, sexual adornments are usually found in one sex alone and not in both. Secondly, they are usually found in the male and not in the female. Darwin believed that Homo was an exception, and that ‘Man, or rather primarily woman, became divested of hair for ornamental purposes’, and that the female subsequently transmitted the sexual adornment of nudity ‘… almost equally to their offspring of both sexes’.