THE USE OF LIMBS
The fragments of myth, folklore and tradition that remain to us from a pre-scientific age are like the marks left in sand by retreating waves: void of power and meaning, yet still possessed of some order. Muddied by time and confused causality, they still bear the imprint of the regularities of the natural world. It is surely significant that in such lore – no matter what its origin – few parts of the human body are as vulnerable to deformity as the limbs. Greek mythology has only one deformed Olympian, crook-foot Hephaestus who, abandoned by Hera (his mother), betrayed by Aphrodite (his wife), and spurned by Athena (his obsession), nevertheless taught humanity the mysteries of working metal and so is the god of craftsmen and smiths. Depicted on black-and-red-ware he is usually given congenital bilateral talipes equinovarus, or two club-feet. Oedipus, perhaps the most famous deformed mortal, wore his swollen foot in his name.
New myths arise even now. In the mid-1960s a Rhodesian Native Affairs administrator claimed that he knew of a tribe of two-toed people in the darker reaches of the Zambezi river valley. In tones reminiscent of Pliny the Elder’s accounts of fabulous races in Aethiopia or the Indies they were, he said, variously called the Wadoma, Vadoma, Doma, Vanyai, Talunda or, most excitingly, the ‘Ostrich-Footed People’ – a primitive and reclusive group of hunter-gatherers who, by virtue of their odd feet, could run as swiftly as gazelles. Veracity was assured by a photograph of a Wadoma displaying his remarkable feet. In 1969 this same photograph appeared in the Thunderbolt, a newsletter published by the American National States Rights Party, illustrating an article which argued that since some Africans had ‘animal feet’ they were obviously a separate species (‘Negro is related to Apes – Not White People’). American academics, rightly outraged, denounced the photograph as a forgery. Wrongly so, for when geneticists investigated the matter, they found that the Wadoma certainly existed, although far from being a whole tribe of ‘ostrich-footed’ people, there was only a single family afflicted with an apparently novel variety of ectrodactyly. But it is impossible to keep a good myth down. In the mid-1980s two South African journalists claimed they had stumbled across a whole tribe of two-toed people in the darker reaches of the Zambezi. Now, websites assert that the Wadoma worship a large metal sphere buried in the jungle and are, in fact, extraterrestrials.
Limbs have an extraordinary knack for going wrong. There are more named congenital disorders that affect our limbs than almost any other part of our bodies. Is it that limbs are particularly delicate, and so prone to register every insult that heredity or the environment imprints upon them? Or is it that they are especially complex? Delicate and complex they are, to be sure, but the more likely reason for the exuberant abundance of their imperfections is simply that they are not needed, at least not for life itself. Children may grow in the womb and be born with extra fingers, a missing tibia, or missing a limb entirely, and yet be otherwise quite healthy. They survive, and we see the damage.
One of the strange things about limbs is how easy it is to compensate for their absence, either partial or entire. As the patriarch of one ectrodactylous family replied to a geneticist: ‘Bless ‘e, sir, the kids don’t mind it. They never had the use o’ fingers and toes, and so they never misses ‘em.’ Indeed, why should they? They could hold their own at school in writing, drawing and even needlework. Among the adults, one was a bootmaker, one drove a cab, and another had a party trick in which he picked up pins from the floor using his two opposable toes.
The neural and physical versatility of limbs is even more striking in people who lack upper limbs altogether. Among the most engagingly feisty of all armless artists was Hermann Unthan, ‘The Armless Fiddler’. Born in 1848 in a small German town, he narrowly escaped smothering by an infanticidal midwife, and was raised by his strict but loving parents on a diet of self-reliance that now seems positively heartless. Within days of his birth, his father ordered that his son was never to be pitied, never to be helped, and was not to be given any shoes or socks. By 1868 the young Hermann was giving violin recitals to delighted Viennese audiences as the younger Johann Strauss conducted. In the course of his long and varied life he travelled widely, finally coming to rest in the United States, which he loved. At the age of eighty he wrote his autobiography, aptly titled The armless fiddler: a pediscript, with his toes and an electric typewriter. This sort of neural flexibility is common in mammals. Among the anatomical wonders of the 1940s was a little Dutch goat that, born without fore-limbs, managed to get about bipedally, rather in the manner of a kangaroo.
THE NEAR TO THE FAR
The ability of animals to survive without their limbs has long proved useful to biologists. Limbs can be counted, dissected and manipulated on a living creature without the need to open the body. They are naked to the biologist’s gaze. This visibility means that, of all the devices that make the body, those that make limbs are now exceptionally well understood. Much is known, for example, about their most salient characteristic: the fact that they stick out from our bodies.
At day 26 after conception, the first signs of a foetus’s arms appear: two small bumps, one on each flank, just behind the neck. By analogy to the precursors of leaves or flowers, these bumps are called limb-buds. A day or so later, another pair of limb-buds forms further down the torso; they will become legs. Like any of the bumps on the surface of an embryo, limb-buds are at first just a bag of ectoderm filled with mesodermal cells. There are as yet no bones, muscles, tendons or blood vessels. The limb-bud remains in this amorphous state for about five weeks, at which time faint outlines of bones – the first signs of structure – begin to form. Even before that, however, the limb-bud has not been quiescent, because from nothing more than a small bump it has grown into an appendage about 2 millimetres long. On day 50 after conception, the embryo crouches and holds its newly formed hands over its heart. On day 56, it touches its nose.
What induces a limb-bud to grow out into space? In 1948 a young American biologist, John Saunders, gave an answer to this question. He had noticed that limb-buds were crowned by a ridge of unusual cells. The cells were clearly ectoderm – the tissue that covers the entire embryo – but at the tips of limbs they resembled tightly packed columns, quite unlike their usual pancake shape. Saunders dubbed this structure the ‘apical ectodermal ridge’ and then, curious to know more, decided to remove it.
As embryonic newts have been used to study the organiser, so chickens have been used to study limbs. Saunders operated on twenty-two foetal chickens, some young, others a little older. In each case he removed the apical ectodermal ridge from one wing-bud, while leaving the one of the other side intact. Having operated, he sealed up the egg and waited until the chicks hatched out. The operated wings all had a characteristic deformity: they were, to varying degrees, amputated. Chickens operated on when the limb-bud had just begun to expand showed severe amputations: they had at best a humerus (the bone closest to the shoulderblade), but below that, the radius, ulna, wrist bones and digits were all gone. Those operated on a little later had a humerus, radius and ulna, but lacked wrists and digits; later yet, only the digits were missing.