Is there any hope for the bald? Contrary to the folklore of depilation, shaving does not make hair grow faster, thicker, or darker – so there’s no point removing what little you have left except on aesthetic grounds. More usefully, at least one of the baldness therapies currently marketed, said to be quite effective, is an inhibitor of dihydroxytestosterone (DHT), the more potent version of testosterone. If this doesn’t appeal (and only a few users suffer impotence as a side-effect), then other therapies may soon be available. The resting hair follicles of a young mouse can be made to produce hair if dosed with a virus expressing high levels of sonic hedgehog. The surplus sonic probably forces the proliferation of the stem cells in the bulge of the hair follicle; if it could do the same for the crippled follicles on bald scalps, then a cure for baldness would surely be at hand. But maybe the hair follicles of bald scalps cannot be rejuvenated; if so, it will be necessary to make new ones. This may well be possible. Mice that have been engineered to overproduce a special form of the protein ?-catenin make entirely new hair follicles at an age when normal mice don’t. Unfortunately, both sonic hedgehog and ?-catenin are extremely potent molecules. Excess amounts of either tend to produce hair-follicle tumors – the product of all those extra stem cells. It may be easy to spur skin to make new hair; rather harder to tame it.
BENEATH THE NAKED APE
Four centuries and two continents apart, Petrus Gonsalvus and Shwe-Maong are startlingly alike. Were Petrus to discard his richly sombre robes with their scarlet facings and knot a lungyi about his waist, the two men could be brothers. Nineteenth-century scientists such as Carl von Siebold and Alexander Brandt were, however, more impressed by the resemblance of the hairy men to orangutans. Influenced by the new Darwinismus they suggested that hairiness was atavistic. This may seem like a version, albeit dressed up in scientific terminology, of the ancient equation between hairiness and bestiality. But the scientists were careful to note that though their subjects may have looked like apes, they were in fact quite human.
One can still, occasionally, come across claims that surplus-hair mutations reveal the fur beneath the naked ape. But there is reason to think that the atavism hypothesis is wrong – at least as applied to these two families. Both the hairy Burmese and Canary Islanders are described as having exceptionally fine, silken hair. This does not really resemble the robust pelt that covers adult apes – nor even human scalp or pubic hair. And hairy as great apes are, they are less so than the hairiest humans. Petrus and Shwe-Maong had noses, cheeks and ears that were covered in hair – exactly where great apes have rather little.
Where, then, does the surplus hair come from? One possible source is the foetus. Around five months after conception every human foetus grows a dense coat of hair. This ‘lanugo’ hair is fine, silky, less than a centimetre long, and enigmatically fleeting. Just weeks after it has grown it is shed again. Were it not for the occasional child born with lingering remnants of lanugo (often on the ears), we would hardly know that it was ever there. It seems likely that the mutation that afflicted the hairy families caused this lanugo to be retained. Instead of switching over to the normal pattern of juvenile, and then adult, hair production, their hair follicles were arrested in foetal mode.
And not just their hair follicles. In his description of Shwe-Maong, John Crawfurd notes that the hairy Burmese man had only nine teeth: four incisors and one canine in the upper jaw, four incisors in the lower, and no molars in either. Shwe-Maong’s daughter, Maphoon, had even fewer. Careful inquiries showed that they had not lost their missing teeth: they had never grown them. It was as if their teeth and hair had simply come to a halt somewhere around the sixth month of foetal development even as the rest of their bodies marched on.
Darwin himself knew of the Burmese hairy family. In The descent of man and selection in relation to sex (1859) he cites the bribe needed to secure Maphoon a husband as proof that hairiness in women is universally unattractive. Nowhere, however, does he suggest that hairiness is an atavism. He is, instead, interested in the connection between hair and teeth. A Mr Wedderburn had told him of a ‘Hindoo’ family in the Scinde – modern-day Pakistan – in which ten men from four generations were almost entirely toothless, but, far from being hairy, were rather bald – and had been so from birth. The bald, toothless Hindoos also lacked sweat glands; unable to perspire, they wilted in Hyderabad’s heat.
Hair, teeth, sweat glands and (though Darwin does not mention them) breasts, organs seemingly so various in their purpose and plan, are intimately connected. They are all places where skin has swollen or cavitated to make something new. The simple tube that is a hair follicle, the robust anvil of dentine and enamel that is a tooth, and the bulging burden of ducts that is a breast, are all variations on a constructional theme. A genetic disorder – there are more than a hundred – that affects one of these organs will often affect another.
These organs do not merely share an origin in skin; they are also made in much the same way. Even as hair follicles are forming throughout the foetal epidermis, other epidermal cells are clumping and cavitating to form teeth or mammary glands. Like the hair follicle, each of these skin organs is a chimera: part ectoderm, part mesoderm.
The kinship between all these organs can be seen in the molecular signals that make them. The ‘Hindoos’ still live near Hyderabad, where, confusingly, they are known as ‘Bhudas’ but are in fact Muslim. By 1934, six generations of Bhudas had spread across eight families. Now there are many more. Their distinctive appearance means that they recognise each other as relations, but the name of their mutant forebear seems to be forgotten. Just as Darwin’s correspondent said, they have neither sweat glands nor teeth (except for the occasional molar), but they do have at least a little scalp hair. They carry a mutation in a gene that encodes a protein called ectodysplasin, named for the disorder its absence causes: Ectodermal dysplasia. A mutation in the same gene may also explain the Mexican hairless dog. Alias El perro pelon or the Xoloitzcuintle, the dog is said to have been bred by Aztecs in the fourteenth century, possibly for meat but more likely as a kind of bed-warmer. It, too, is bald, toothless and has dry and crinkly skin for want of sebaceous glands.
An even deeper organ-kinship is evident in an odd variety of aquarium fish. Since at least the start of the Tokugawa Shogunate in the early seventeenth century, Japanese fanciers have bred the Medaka, Oryzias latipes, a small fish that normally lives in rice-paddies. A sort of poor man’s Koi, they can be bought from the night-stalls in Japanese cities where, among the varieties for sale – albino, spotted, long-fin – there are mutants that have no scales. The Medaka’s nudity, like the Bhudas’, is caused by a mutation that disables ectodysplasin signalling.
The use of a single molecule in the making of human teeth, hair follicles and sweat glands is a legacy of the evolutionary history that these organs share. This history is evidently also shared – at various removes – with the feathers of birds and the scales of fish and reptiles. All these organs have evolved from some simple skin organ possessed by some ancient, long-extinct ancestor of the vertebrates. No one knows exactly what this organ was. The best guess is that it resembled the tooth-like scales that give shark skin its roughness.