9
Future Skeletons
The asteroid that slammed into what is now the Yucatan Peninsula of Mexico, 66 million years ago, was about 10 kilometres across, or the diameter of a moderate-sized city. The energy instantly released was about a billion times that of the Hiroshima and Nagasaki atom bombs combined, creating a crater some 180 kilometres in diameter. The powerful shock waves, rippling around the globe, may even have helped provoke bursts of volcanism in India, then exactly on the opposite side of the globe. Enormous tsunami raced across the oceans, firestorms were triggered, enormous amounts of soot and dust in the atmosphere probably triggered some kind of ‘nuclear winter’ cooling for years, and the oceans were acidified from the sulphates released by the impact.
The exact kill mechanisms are still hotly debated by scientists, but kill they did, and kill most effectively. When the dust settled, there were scarcely any animals alive on land larger than 25 kilograms. The non-avian dinosaurs84 had been wiped out, and the ammonites and belemnites had disappeared from the seas. It was the fifth major catastrophe to strike life on Earth in the past half-billion years. It was not the most severe of these crises—the volcanism-triggered Permian–Triassic extinction event, 252 million years ago, takes the palm for that—but it was almost certainly the most abrupt. Life had to reorganize itself, once more—and design new skeletons to replace the spectacular ones that had been so suddenly discontinued. There are many stories surrounding this particular reorganization, but the story that is in our bones, so to speak, is how mammals emerged from the shadows of the dinosaurs, after that catastrophe, to dominate both land and sea.
The mammals’ sojourn in the shadows had certainly been an extraordinarily long one. Throughout the whole of the Jurassic and Cretaceous periods (and in part of the Triassic Period before that), they were present on Earth. This is clear, even though most of the features that we associate with mammals—the fur, sweat glands, mammary glands, the way they care for their young, and so on—do not fossilize easily. However, the early mammals can be recognized from their specialized teeth, which form a familiar package of incisors, canines, premolars, and molars. Such teeth—the hardest part of their skeletons—consistently turn up in strata in which there are dinosaur bones. Their equally consistently diminutive size, though, indicates that mammals then were small, mostly varying from the size of a mouse to that of a domestic cat. The largest known seem to have been about as big as a badger, like Vintana, which lived in what is now Madagascar in Cretaceous times, and the similarly sized Repenomamus, also Cretaceous, from China. And of those that survived the end-Cretaceous meteorite impact, none seems to have been larger than a rat.
That newly emptied ecospace, though, offered possibilities to those diminutive survivors, now that the dinosaurs were gone from the top spots of the food chain. From those small beginnings came a cornucopia of new mammals that evolved into an extraordinary range of forms. Even the first 10 million years after the disaster, the time of the Paleocene Epoch, showed a transformation. From the rat-sized mammal survivors, larger and more diverse forms quickly began to evolve. Less than a million years after the impact, at least one mammal, Wortmania, had reached 20 kilograms in bulk. Then, there came heavy-boned large herbivores such as Barylambda, in shape something like an early version of a giant sloth that could weigh more than half a ton. There was the fearsome-looking Titanoides—the size of a pig, with huge sabre-like canine teeth and clawed feet, it was nevertheless likely to be a herbivore, digging for roots. Carnivorous mammals had appeared, strange animals like Psittacotherium, the ‘parrot beast’ with massive front teeth drawn out in beak-like fashion.
That was just the first 10 million years. In the succeeding Eocene and later epochs, the array of descendants from those original rat-like ancestors continued to diversify. There was the 2-ton Eocene Uintatherium, about the size of a rhino or hippo, with a little of the appearance of both. It was the kind of beast that may have been preyed upon by the mysterious Andrewsarchus, known only from a single metre-long enormous lower jaw, embellished with fearsome teeth, discovered in the wilds of Mongolia nearly a century ago—perhaps the largest carnivorous land mammal ever. These were impressive beasts, but were later eclipsed on land by Indricotherium, whose 20-ton bulk brought it near to the size of the giant sauropod dinosaurs, and in the oceans by the whales, including the blue whale, the largest animal ever to have lived on Earth. These, and the horses, camels, elephants, tigers, gorillas, tapirs, and many more—all (including the blue whale) were derived from those tiny furry rat-like ancestors in just 66 million years. Their bones, when unearthed now and again by the ancient Greeks and Romans, were often interpreted as those of giant humans—either ogres or heroes. A source of awe and fascination, and revered as sacred relics or as talismans to bring good fortune in battle, they were among the celebrity items of those times, and a good discovery could spark off a bone rush.85
The evolved animals hang, of course, from an evolved bony framework. Consider the jaw of the rat-like ancestor, a couple of centimetres long, weighing a few grams, and ending in sharp teeth. Then fast forward a few tens of millions of years, and then take the 107 bus route in Barnet, London, stopping off at Wood Street by a house called The Whalebones. There is an entrance arch to the driveway—which is made of a pair of real blue whale jaws anchored into the ground—their original owner having been hunted to death in the South Seas. Approaching 7 metres long and weighing about a ton and a half, in life they would not have had teeth, but sheets of baleen for the filtering of plankton from seawater.
The strange and rather grisly memorial in Barnet gives pause for a good deal of thought, but one conclusion might be that it shows what evolution can do to a skeleton, over a time span of about 1% of the age of the Earth. Just to hammer home the point of the sheer variety, and quirkiness, of the process, one might look at a smaller, though no less remarkable, cousin of the blue whale, the narwhal. This is one of the toothed, rather than baleen whales, though it is in the most literal sense a singular phenomenon. Virtually all the teeth have been lost in its evolution, save one of the canine teeth. In the male (and in some females) this tooth grows straight out in front of the animal, reaching a length that can exceed 3 metres, to become the defining characteristic of this ‘unicorn of the sea’. The giant single tooth is a multipurpose tusk, crammed with nerve endings that transmit information about water conditions to the whale’s brain, and, it has been suggested, to other whale brains, too, when whales rub tusks together. The tusk, too, can be used to strike and stun small fish that are the whales’ prey. This is a science-fiction skeleton—but one that exists in reality, produced by nothing more than Darwin’s marvellous mechanism and modest amounts of geological time.
Preparation for a Sequel
It is hard to imagine, now, what the Earth’s biological richness used to be like, until geologically recently. We have an abundance of vertebrates on land right now—perhaps an abundance that has never been matched at any time in our planet’s history. But this abundance is now concentrated, just as uniquely, within a tiny, all too familiar, set of creatures—us and our farmyard animals. The wild vertebrate land animals of the world are now pushed to the margins, their combined mass amounting—as the scientist Vaclav Smil has estimated86—to less than 5%—perhaps even under 3%—of the mass of us and our selected prey animals.
Most of the species that were present a century or two ago are still here. But that number, as regards large mammals, was already reduced. Between 50 000 and 10 000 years ago, the number of large animals was hugely depleted, with the loss of some 90 genera of animals weighing more than 44 kilograms,87 approaching half of the total. Among the disappearances were sabre-tooth tiger, giant sloth, and mastodon in the Americas; mammoth, woolly rhinoceros, auroch, and giant deer vanished from Eurasia; and the rhino-like Diprotodon and giant wombats disappeared from Australia. Climate change may have been implicated, but climate had changed many times over the previous few million years, without sparking extinctions. Almost certainly, this wave of extinctions was humanity’s first significant mark on the Earth, via a formidable, honed skill at hunting.
In the 11 700 years of the Holocene, the scale of these extinctions was only matched when humans discovered new terrain: New Zealand, for instance, had been inhabited by several species of that large flightless bird, the moa, the largest well over 3 metres in height, preyed upon only by the huge Haast’s eagle. At about ad 1300, the Maori people arrived, and little more than a century later all moas—and the eagle—had disappeared.
The remaining large wild animals have been confined to what is left of the Earth’s wilderness. Now, that wilderness is receding quickly, with humanity’s extraordinary growth, from about 1 billion in ad 1800 to about 3 billion in 1950, to 7.35 billion now, and heading towards 11 billion by mid-century. Extinction rates globally have gone up by an order of magnitude over the last century, and may now be something like a thousand times over background levels. If these trends continue, how long to the next full-scale mass extinction? Anthony Barnosky and his colleagues’ work suggests that, with business as usual (and not including the effects of climate change), it will take just a few centuries for a mass extinction, rivalling that at the end of the Cretaceous, to take place.88
Let us hope that this tragedy (for there is no other way of putting it) will not come to pass. But, currently, the growing pressures show no signs of abating. It seems more likely than not that, geologically very soon, there will be another emptying of ecospace. And humans themselves—living more quickly and more dangerously than any other species, might be among the casualties. Taking the long view ahead—what then?
Bones of the Sequel
The palaeontologist Dougal Dixon has been called the founder of speculative evolution. He imagined a world shorn of many species because of man, and then shorn of man—and left for 50 million years. He populated this world with a plausible but entirely imaginary new suite of animals, evolved from the survivors that were left After Man,89 as the first of his books on this theme was titled. If the elephants became extinct during the brief human empire, he said, perhaps their ecological position could be filled via the evolution of some of the few surviving antelope. The result he called the gigantelope, an elephant-sized animal where the antelope horns have stretched out and coiled forward to take the place and the function of the tusks. With true anteaters extinct, their niche he imagined to be taken over by the turmi, survivors of pigs, their snout bones extended and with horns outwardly turned to dig into termite nests, and a lower jaw that has lost teeth, becoming a narrow channel for the long, termite-gathering tongue. Among Dixon’s predators is the sinister-looking strider, a descendent of a cat adapted with limbs greatly extended and armed with grasping claws to swing through the forest branches in search of prey.
He provides many more examples. It’s a beautifully imagined (and drawn) picture of what the biology of the far future might be, over a time roughly similar to that of the Cenozoic Era. Indeed, given what we know of the extraordinary animals of that era (still, remember, the one in which we live) it is a little conservative—Dixon does not posit anything quite as extreme as the something like 100 000-fold increase in mass of the jaw (and total restructuring in shape) from that of the end-Cretaceous mammal survivors to that of the blue whale. Truth can be stranger than fiction, even properly scientifically imagined fiction.
Dougal Dixon focused on the mammals, to provide a ‘futurized’ mirror image of their spectacular Cenozoic evolution. To obtain a more rounded view of future skeletal evolution in a human-free world, we need to spread our net more widely among the other groups of organisms. Among the reptiles, the snakes are managing to stay among the survivors of the human onslaught, and some even appear to be the winners, like the pythons introduced into the Florida Everglades, now exploding in population and seemingly unstoppable as a voracious predator. Will such redistributed survivors ever evolve into a snake the size of the Paleocene Titanoboa? Reconstructed from a few enormous fossil vertebral bones, this snake is thought to have been in excess of 12 metres long and to have weighed significantly over a ton.
Of course, there are the invertebrates to think of, too.
The Next Reef Gap?
As the year 2015 turned to 2016, the Pacific Ocean began one of its periodic changes. Warm water began to spread from its western part to its eastern part. This is El Niño, part of a climate oscillation that has taken place every few years for thousands, and probably millions, of years. It brings with it flooding to the western Americas, and drought in the west Pacific, India, and Australia. It has brought collapse of anchovy fishing off Peru, and famine to Africa and to Europe too, may have brought about the demise of pre-Columbian cultures in South America, and perhaps helped spark off the French Revolution of 1789. But in early 2016, there was another victim. It was the Great Barrier Reef.
As the waters off eastern Australia warmed to levels probably not experienced there for many tens of thousands of years, the corals of the Great Barrier Reef began to suffer heat stress. This triggered their classic reaction: expulsion of their zooxanthellae, which removes both their colour—bleaching the formerly vividly coloured coral animals to a ghostly white—and a major source of nutrients. The more severely bleached corals died soon after.
Much of the damage was in the north, where over 60% of the coral cover was bleached. The south—normally more vulnerable, and more damaged by human activities in general—was largely protected by a vagary of the weather: the passage of a hurricane there, early in the year, cooled the waters sufficiently to prevent most of the bleaching. Without that freak event, the damage would have been much worse.
As we write, in 2017, the damage did just become worse. Although El Niño is receding, the waters in this Australian summer were still hot enough to severely bleach corals in the mid-section of the Great Barrier Reef. In these 2 years, some two-thirds of the Great Barrier Reef has suffered severe bleaching. It is not just this iconic Australian reef that has suffered. Again, as we write, the warming waters in the South China Seas are decimating the corals. Around Dongsha Atoll, there was a local heat amplification effect, raising the temperature of the water by as much as 6°C above normal, and some 40% of the reef corals have died. The whitened reef skeletons are now darkening as the coral tissues putrefy.
Some 50% of the world’s coral reefs have already been lost by a combination of heat, pollution, and disturbance. The heat is now taking on the main kill role, far earlier than expected. A few years ago, scientists were more concerned about the effects of increasing ocean acidification, as human-produced carbon dioxide continues to dissolve into the seas, over the coming century. Now, the (real) threat of acidification has been eclipsed by the effect of rising temperatures, with projections that 90% of the reefs will be gone by mid-21st century—and the warming, of course, is not likely to stop after 2050.
Temperatures look set to rise still further over coming decades. Now, bleached coral, if it has not been killed off completely, can recover, given sufficient time—a decade or two—to grow back. But with carbon dioxide levels and temperature set to rise still further (there are no signs yet of a slowing in this trend, let alone a reverse of it), the prospects of more bleaching events look high, and the prospects for coral reefs as functional ecosystems—and as producers of skeletal rock in large amounts—look bleak. Only a quick and dramatic slowdown in carbon emissions is likely to prevent this, and again, as we write, this does not seem likely. Rapid collective action on global environmental problems is currently not a well-developed human trait. The planetary mega-skeletons that are coral reefs look likely to disappear once more—the last time was 55 million years ago—from the Earth. We hope we are wrong, but on current evidence, reef extinction seems much more likely than not. In the words of one scientist, the reefs might already be zombie ecosystems—the living dead of the oceans.
Perhaps one might seek scant consolation in looking very, very far ahead to see what might ultimately arise, phoenix like, from the ashes of the world’s current reef systems. So—if today’s reef-building corals have been too badly damaged—or soon will be—to make a comeback, once Earth’s temperatures begin to decline from the climate hyperthermal and ocean acidification event that is now beginning: what might take their place?
When the reefs died out 55 million years ago, they were replaced in many places by ecosystems dominated by those skeleton-making protists, the foraminifera, before the scleractinian corals eventually made a comeback—though these ecosystems had nothing like the strength and geometrical (and ecological) complexity that interlaced coral skeletons can provide.
We live, now, in an era of shelled molluscs, notably the bivalves and gastropods—a dominance that started when the dinosaurs walked Earth and that has only grown since then. Perhaps, therefore, some skeletons similar to those of the tube-like rudist bivalves of Cretaceous times will evolve again, and begin to build enormous collective structures on future warm and shallow sea floors. Perhaps the coralline algae—less sensitive to temperature than the delicate corals—can still form the leading edge of reef-like structures. Let us hope that we would not go back to a world of stromatolite reefs like that of the Precambrian—for that would mean that humanity would really have collapsed life down to its primeval basis.
Designer Skeletons
When Mary Wollstonecraft Godwin was just 18 years old, she had been the lover of the poet Percy Bysshe Shelley for 2 years. She, Shelley, and her stepsister Claire Clairmont went to stay for the summer of 1816 at a villa by Lake Geneva, to be with Lord Byron and his physician, John Polidori. The atmosphere was an intense mix of passions, intrigues, and intellectual adventure, focused all the more because this was the ‘year without a summer’, the eruption of the volcano Tambora the year before having affected the world’s climate. Cooped up in the villa in the miserable weather, they amused themselves by recounting stories of the spirit world, and Byron challenged everyone to write their own ghost story. It was one of the most productive calls in the history of literature. Two monsters emerged that would shiver spines around the world from then onwards. Polidori wrote The Vampyr based on a Byron poem, and started the vampire horror story genre. And Mary Shelley (as she had started calling herself then), after days vainly seeking inspiration, had—between 2 am and 3 am on 16 June 1816—a vivid ‘waking dream’, and began to write Frankenstein: Or, the Modern Prometheus.
Frankenstein’s monster is a classic tale of disastrous human hubris, as the brilliant but flawed Dr Frankenstein cobbles together the unfortunate creature from various body parts taken out of slaughterhouses and dissection rooms. Eight feet tall because the ambitious doctor struggled with the fiddly detail of anatomy, and repulsive because the skin was stretched too tight over those huge bones, the invented, sensitive, and unhappy monster duly went on to unleash mayhem on the world at large—and, finally, with appropriate literary even-handedness, upon the over-ambitious doctor too.
Designer humans are not (quite) with us yet. But designer animals have been with us for some time. Charles Darwin, in writing On the Origin of Species, was famously dismissive of the ‘paltry’ geological record as evidence for his new theory of ‘descent with modification’. But he noted how, in natural designs, there were relics of the old hidden among the structures of the new. Hence, the whales, thoroughly reshaped from their ancient furry ancestors to become, in effect, very big fish-like animals, nevertheless contained bones that represented the pelvis, femur, and tibia. And he positively enthused about the work of the animal breeders.
Pigeons, and what humans have done to their form, take centre stage in the first chapter of the Origin. Darwin said that he had ‘kept every breed that he could purchase or obtain’, and indeed had a large and thoughtfully designed pigeon loft at Down House, and probably a competent loft manager too; otherwise, he would have got little other work done. He proudly stated that he had been ‘permitted to join two of the London Pigeon Clubs’, these probably being of the type that kept the membership rate as high as a guinea ‘to keep the Spitalfields weaver types out’.90 He marvelled at the variety of the different breeds, where the differences were not simply of plumage but affected the basic bone structure of the bird. In the skeletons, he said the bones of the face could differ in length and breadth and curvature ‘enormously’, and that of the lower jaw ‘varies in a remarkable manner’. Different breeds had different numbers of ribs, and of vertebrae, and the wishbone could be of a different shape. This was fundamental human-driven re-engineering by selective breeding from the basic design, that he considered to be all derived from the rock dove, with considerable change being possible in just a century.
It was not just pigeons, of course, and Darwin’s focus on the work of the animal breeders was to show just how far the fundamental skeletal shape of an animal could be driven from its original, wild structure. Where there have been millennia, not centuries, for humans to reshape an animal then the results can be remarkable. Dogs have been domesticated for at least 14 700 years, since the times of hunter-gathering at the tail-end of an Ice Age. From the original wolf-like ancestor there now have evolved—to give just a few examples—chihuahuas, St Bernards, dachshunds, terriers, greyhounds, miniature Schnauzers, and mutts. Give the bones of each of these to a palaeontologist and he or she would probably diagnose a separate species, based on skeletal characteristics alone.
How quickly can the animal breeders work? Dr Frankenstein would have tipped his hat to the animal reconstructionists of the Chicken-of-Tomorrow programme that started in the USA of the early 1950s, aimed at providing bigger, faster-growing chickens. Chickens had been domesticated for a long time—not for as long as the dog, but since about 2500 bc in south and southeast Asia, the wild form being the Red Jungle Fowl of those parts, a lean, fast-running bird that can live for more than 15 years. Domestication was a success, with the bird being spread by migrants and traders to the Near East and Europe of the Roman Empire, and then carried with the colonists to the New World. Scratching around wherever there were humans, and providing both eggs and meat, the domestic chicken seemed always to be there. Over that time, though, it didn’t change drastically. Indeed, establishing the earliest dates of domestication is a problem because the bones of the wild and early domestic forms are so similar. Later on, in places like Europe where it was clear that this bird was introduced, there was a good deal of stasis. Archaeologists often find the bones around Roman and Medieval sites, and have kept track of any changes via standard measurements. A common and recognizable bone is the tibiotarsus, the lower leg bone of the chicken, corresponding to the human tibia, but with several bones of the tarsus (foot) fused to it. The tibiotarsus, through a couple of thousand years, did not vary greatly in dimensions, other than becoming a little thicker at the end overall around the Middle Ages.
Things began to change in the late 19th and early 20th centuries, but the changes moved up several gears once the Chicken-of-Tomorrow team got their hands on the post-World War II chicken. In less than 50 years, the tibiotarsus became more massive, doubling in breadth. The whole chicken, from the wiry and scrawny prewar form, was remodelled into the modern broiler bird, which is four to five times heavier. It is a giant—but an enfeebled giant, for it has been bred not just to be huge, but to grow to be ready for the table from hatching in just 6 weeks. Those enormous bones are riddled with deformities and useless—the bird cannot fly and can barely walk, as its hypertrophied breast muscles cause it to tilt forwards. It can only live its short lifespan due to continuous human intervention (and, even if rescued from the battery farm, will quickly die anyway). This—the Anthropocene chicken—is now by far the commonest bird in the world, the standing stock of more than 20 billion dwarfing the numbers of the commonest wild bird (the red-billed quelea of sub-Saharan Africa, at about 1.5 billion breeding pairs) and being further multiplied by the rapid turnover of that absurdly short lifespan. Moreover, people carefully put the bones, after a chicken dinner, into the trashcan for burial in landfill sites—a contrast with the rapid scavenging of almost all wild bird bones after death. This tidy human habit means that the modern broiler chicken will certainly provide some of the iconic fossil bones of the Anthropocene Epoch.91
There will be, too, the bones of the cattle, pigs, sheep, goats, and other domesticated animals that humans have shape-changed too and that—together with us humans—now make up 95% or more of the mass of medium to large vertebrates on land. The smaller vertebrates, by the way, are harder to count, but are not likely to change this figure much; the number of perhaps the most abundant of these, the brown rat, seems to be roughly comparable to the number of humans worldwide, about 7 billion: as they average about a third of a kilogram each compared with the average human weight of 62 kilograms, the total brown rat biomass will weigh in at about half a percent of that of total human biomass. Bones of all the domestic animals are, like those of the chicken, tidied away into landfill sites by their human predators, often carefully plastic-wrapped to aid future fossilization.
This explosion of artificially buried bones are, furthermore, dismembered and/or sawn through in a manner quite distinct from that of ancient bones, which in past geological epochs were torn apart or crunched by the claws and teeth of predators less ingenious and technically sophisticated than are modern humans. We really have reached a kind of peak of skeleton production in this respect. Anthony Barnosky of the Stanford University has calculated that the total mass of land vertebrates is now on the order of ten times what it used to be before humans took control of the food web on land and—crucially—turbocharged it by adding geologically unprecedented inputs of phosphorus (taken from certain, rare rock layers in the ground) and nitrogen (extracted from the atmosphere in the energy-intensive Haber–Bosch process that converts inert nitrogen into usefully reactive ammonia for fertilizers). The crop plants that we now grow so abundantly are mostly fed to our few species of hyper-abundant captive animals before these are fed to us, in this remarkably expanded and modified new global chain of skeletons.
All of this was essentially achieved with just selective breeding, a millennia-old custom, boosted by fertilizer use. Today, the use of the Frankenstein label is mostly with respect to the new technology that has appeared, to remodel biology yet further: genetic engineering, where the animal is altered by direct manipulation of its genes. It is early—and controversial—days so far, and this kind of engineering is mainly directed at cryptic qualities—at least as far as the skeleton is concerned. There are pigs that are modified to excrete less phosphorus, and cows modified to produce low-lactose milk, and even goats that have had silkworm genes inserted into them, in the hope that silk can be woven from an extract of their milk. Things are moving quickly. We suspect that new forms of skeleton, designed in the genetic engineers’ labs and putting the Anthropocene chicken in the shade, are not far away.
Of course, one does not need a genetic engineer to modify a skeleton. A real engineer will do.
Augmented Bones
When human skulls from the Neolithic culture are uncovered by archaeologists, as many as one in ten can show a neat round hole in the top of the skull, many with the edges of the bone healed, showing that the owner had survived the hole-making process. This is the result of trepanning, a widely practised operation across both the Old World and the New World, from Stone Age until Medieval times, where a neat hole is made into the skull by either drilling or scraping the bone away. Why was it done? Perhaps, to release evil spirits, or treat recurring headaches. It was a surprisingly widespread practice. For many millennia too, humans have also set bones, or carried out impromptu amputations, following accident or battle—and their skeletons suggest that at least some of these operations were successful. There are also cultural costumes—making the ‘lotus feet’ of women in China, for instance, a practice that spread through society from the 10th to the 19th centuries. Here, young girls had their feet bound, and toes systematically broken, to achieve the socially desired shape. These were not miniaturized perfect feet, but something more akin to a club foot with permanently deformed bone structure. This practice was agonizing in the making, and painful and difficult to walk on ever after; it was only stopped, by systematic central government pressure, in the 20th century. Or the ‘giraffe necks’ of the Kayah tribe of Burma, created by inserting successive copper brass rings on to the necks of female children as they grow, the column of rings then kept throughout life. These do not involve great pain as with the lotus feet, and it is not so much the neck that is stretched, as the rib cage beneath that is compressed. Humans have modified their skeletons for a long time.
And added to them, too. Pirate stories, for some reason, have advertised such augmentation most vividly, though in part mendaciously. J.M. Barrie, in creating the eponymous Captain Hook, for instance, spread through popular culture a vision of both pirates and prosthetics that did not exist in reality. Pirates, true, were prone to losing limbs—but the ship’s doctor was also usually the ship’s cook, presumably because of their everyday practice with carving knife and chopping board. When their patients did not die of gangrene, their remaining stumps would have probably been too painful and mutilated to insert a useable hook, either by surgery or by some complicated kind of harness. An artificial leg of wood, though, seems to have been a more realistic project, and the genuinely fearsome 16th-century French privateer Francis Le Clerc seems to have served as a model for his many descendants in storybook and film (and, occasionally, in real life). Losing one leg during an act of piracy, he had it replaced with a wooden leg and went from strength to piratical strength, being known as ‘Peg Leg’, ‘Jambe de Bois’, and ‘Pata de Palo’ by the awed crew members of the English, French, and Spanish vessels that he attacked without fear or favour. Among his exploits, he devastated the then capital of Cuba, Santiago de Cuba, to such an extent that the city never recovered, and Havana was to become the new capital. His end was appropriate. Refused a pension by Queen Elizabeth I of England (having requested it for his plundering of French shipping) he went on to die with his boots on—or with at least one boot on—in attacking Spanish treasure ships.
Things have moved on since then—and are still moving, ever faster. Augmented skeletons are now safer, much more commonplace, much less melodramatic—and much more integrated. When somebody’s natural ball-and-socket hip joint wears out today because of old age or disease, part of the upper leg bone can be cut out, to be replaced by a titanium alloy (the ball can be made of alloys of chromium, cobalt, and molybdenum), while the hip socket joint can be removed and replaced by metal, ceramic, or plastic, the whole being fixed to the remaining bones by acrylic cement. Today, some 2.5 million Americans have such artificial hips, about 0.8% of the US population. An infirm knee can be replaced by a cobalt, chromium, and plastic replacement: about 4 million Americans have these, about 1.5% of the population. A broken leg can be pinned by metal, or a broken skull augmented by metal to replace crushed bone. Most commonly by far, a tooth ravaged by sugar in the modern diet can be filled with amalgam, an alloy of mercury, silver, tin, and copper. In the UK, more than 80% of people have at least one tooth filling, and among those, the average is seven fillings per mouth. Most modern human skeletons are re-engineered in one way or another—to permanent, and indeed future palaeontological, effect.
The range of augmentation is now widening rapidly, as the ever-accelerating technological revolution expands to include the human body. Metal bone implants for growing children can now be made bionic, incorporating motors guided by electronic signals, to extend in length inside the body as the children grow. Bionic arms now begin to include moveable fingers with motors, linked to electrodes that respond to signals from muscles in the remaining natural limb. Such augmentation can trump biology—the wrist on such a bionic hand can easily be made to rotate through 360 degrees. The bioengineers who are now speeding the evolution of these devices already talk of being able to replace 50% of a human body by manufactured parts, and aim to link artificial bones with artificial organs and skin into functional systems. How much, the ethicists who these days are part of such design teams ask themselves, of the human body can be replaced before we can no longer say that the result is still human?
It is a good question, because this kind of internal evolution is now colliding with an external evolution that has been taking place among humans for many thousands of years. The ancient Greeks and Romans were among many who appreciated the value of a good homemade exoskeleton.
Do-It-Yourself Skeletons
It is not quite true that only humans can build and modify skeletons. Those skilful protozoans, the agglutinated foraminifera, carefully select size-graded sand grains and shell fragments to build their own combination of exterior armour and living chamber. The caddis fly larva does much the same, as do, in their own way, the remarkable graptolites, both living and dead.
As well as adding to the permanent skeletal mass, humans have been adept at devising temporary additions, from very early days. Creatures without anything special in the way of teeth and claws, after all, needed to be able to improvise, and to improvise quickly and well, to survive. From sharpened flints and antlers, to swords, lances, and arrowheads, the offensive capability developed as a constant of virtually every human society. And because much of the offence came to be directed towards other human social groupings, there was a need to improvise temporary defensive exoskeletons too. Shields, helmets, and armour duly emerged in an arms race similar to that started by that first shell-bearer, Cloudina, and its unknown assailant some 550 million years ago.
The arms race created its own myths. That of the Battle of Agincourt in 1415 (Figure 41) was gilded by Shakespeare’s narrative powers: that famous day where the arrows of a handful of English archers cut through the suits of armour of the onrushing French aristocracy. It wasn’t, though, quite like that quintessentially patriotic account of valour and technological advance. Henry V’s 5000 archers did indeed unleash a downpour, probably over 100 000 in a few minutes, of the special ‘bodkin’ arrows designed to penetrate plate armour, as the 8000 armoured French knights rode on their armoured horses or ran across the 250 metres or so that separated the two lines. In such a deadly hail, not one of these knights should have been left alive. But the defensive armour did its work, the English arrows mostly bouncing off French steel plate, and the French army reached the English lines. But the armour was heavy and the ground underfoot, a rain-sodden wheat field, quickly became a quagmire. The exhausted, now almost immobile aristocrats in their heavy metal casing (greedy for anticipated ransom money, they had pushed the professional French soldiers out of the way to be first in the front line) were cut down not with the longbow, but, as the historical writer Bernard Cornwell put it, ‘by all the ghastly paraphernalia of medieval hand-to-hand fighting’—weighted metal hammers, poleaxes, mauls—the horror increasing as Henry V, fearing another attack, ordered all the newly captured French slaughtered. In the struggle for survival, the arms race does not always follow a straightforward course, and it is not only nature that is red in tooth and claw.
Figure 41. The massed ranks of the ‘exoskeleton’-clad French and English soldiers at the battle of Agincourt, 25 October 1415.
Our home-made exoskeletons—and tooth and claw substitutes—have developed apace since then, as Kevlar bullet-proof vests evolve to keep up with advances in bullet technology, tanks vie with artillery shells, and, yet more remotely from the frail human body, satellite-borne lasers lie in wait for nuclear-tipped missiles. Not quite all of these inventions, though, are in the service of the military forces of our modern tribes.
Much like a hermit crab exploiting a discarded gastropod shell—or these days, sometimes a discarded plastic bottle top—for locomotion with added shelter and protection, many of us now climb into our cars each day to commute to work and back. The carefully designed steel panels and bulkheads of our automobiles are not just there to keep the traveller sheltered from rain and wind, but to give protection from other such high-speed wheeled exoskeletons, or from immobile walls or trees, that might be encountered at speed. This is now a new normality for the human species, and these forms of metal cladding can be modified to fly us far through the air and even into outer space, where the astronaut can also use the closer-fitting and more flexible exoskeleton of a space suit, to better explore this inhospitable, airless, and almost endless new realm.
New types of personal hardware are also evolving closer to home, in peace and in war. Newspapers report that the defence industry is preparing ‘wearable robots’ to create platoons of soldiers with increased load-carrying capacities. Biomedical engineers have already devised similar bionic external frameworks to allow people who have lost the use of their legs to walk once more. This is futuristic stuff—of a future that already seems to be here. And, as it is the same technology at the heart of artificial exoskeletons as underpins artificial endoskeletons, the boundaries of what is outer and what is inner seem set to blur as this dizzying progress proceeds. One might say that the important thing about staying human, as our physical framework is reshaped by our own ingenuity, is the human mind and—in some kind of meaning—spirit.
But will our super-strength, augmented humans be guided by super-strength, augmented minds too? As the bioengineers create new kinds of artificial skeleton, and artificial organs and skin too, the computer scientists are making giant strides with artificial intelligence and autonomous systems. One wonders quite where this will take us, and what will become of the world that we live on. Perhaps it is time to take leave of this Earth, seemingly evolving in the geological blink of an eye to some new state, and see what kind of skeletons one might expect on other planets.