The Wild Life of Our Bodies: Predators, Parasites, and Partners That Shape Who We Are Today Read online

  One hopes for a breakthrough, a great and leaping moment of “Aha!” None came. White published a small paper on the find in 1994, more to spray his territory than as a revelation.4 At that point, nothing yet seemed done. What seemed particularly unresolved was the broader story of who these bones belonged to—what she ate, how she moved, and, more generally, how she lived. White and his colleagues would have to have all the bones in place to see that. Once they did, they would be able to compare this skeleton to other younger ones and, of course, to their own bodies. What White and company wanted to see were the differences. Some things in particular would be telling: the size of the skull and hence the brain, the shape of the hips and thus how this woman walked, and the feet. (It could be said that biological anthropologists have a thing for feet; the point of a toe can mean the difference between a foot that clings to a branch and one that sprints.) Nor were the intricate bones all that White and his crew sought. They also gathered the other fossils they found around this woman, all of them—other animals, even the remains of plants. They wanted to see this whole world for what it was, whatever that might be. Jamie Shreeve, a National Geographic editor, has described White as being “hard and thin as a jackal,”5 but maybe he is more like a hyena, an animal that gathers all that it can from each broken-down piece of bone.

  White and his team scarcely talked to anyone about what they were doing. No one outside the group knew exactly what had been discovered. Details were leaked one year to the next, but the details seemed to conflict, almost as though false clues were being left intentionally. Meanwhile, what White was beginning to think was that the woman in the sand—Ardi, as he would affectionately come to call her—was the earliest complete skeleton of a human ancestor.6 If so, hers would arguably be the most important hominid fossil ever discovered. This was enough to keep White ardently at his work. In fact, ardent does not begin to be a strong enough word.

  As White and his team worked, it was clear that the bones they were assembling looked, in many ways, human. The differences between what White and his team had found and the bones of modern humans were, in the broader context of evolution, tiny. She may have been 4.4 million years old, but much of her was like a human child. The same would have been true for her organs and cells, had they lasted. She was like us for the simple reason that the main features of our bodies evolved far earlier than the earliest hominid or even the earliest primate. To find the bones of animals with much different parts, you must go far deeper into the layers of dirt. By the time Ardi was born, we were almost completely who we are today, minus a few bells and whistles, or perhaps better said, big brains, tools, and words.

  Most of our parts evolved in some context not only different from that in which we use them today but different even from that in which the fossil woman discovered by White would have used them. We share nearly all our genes with chimpanzees and, even more, Tim White would come to argue, with the bearer of the bones he discovered. But we also share most of our traits and genes with fruit flies, a fact upon which modern genetics depends for its succor and funding. We even have many genes in common with most bacteria, genes that exist in each of our cells.

  The layer in which Tim White was studying his fossil find was, at its deepest, about two feet beneath the surface of the desert sand and sediment. Two feet is the depth of sediment that built up across 4.4 million years, sometimes a few grains at a time, sometimes more. The layers of sediment in which fossils and history are trapped are not laid down evenly, but if they were, the layer in which the story of life begins would be nearly half a mile in the earth. At the bottom of that sand pile, one can find the era of the first living cell. Already it was a little bit like each of us. It had genes that we still have, genes necessary for the basic parts of any cell. Between that moment and Ardi was the origin of the mitochondria, the tiny organs in our cells that render energy from non-energy, the first nucleus in a cell, the first multicellular organisms, and the first backbone. When primates show up, just thirty feet below the surface, the depth of a well, they were small, runty even, and, no offense, not very smart, but they were already nearly identical to us genetically.

  When the individual that White found had evolved, our hearts had been beating, our immune systems had been fighting, our joints clicking and clacking, and our parts otherwise being tested in our vertebrate ancestors against the environment for several hundred million years. Across these vast stretches of time, climates waxed and waned, continents moved against each other. Yet a few realities remained unperturbed by these machinations of dirt and sky. The sun rose and fell. Gravity pulled every action and inaction to the earth. Parasites attached themselves. No animal has ever been free of them. Predators ate everything; no animal has ever been free of them either. The pathogens that cause disease were common, though perhaps less predictably present than parasites and predators. Every species existed in mutual dependency with other species, in relationships that evolved essentially with the origin of life. No species was an island. No species had ever, in all of that time, gone it alone.

  All these things were true not just across most of Ardi’s life, or most of primate evolution, but since the very first microbial cells evolved and another cell realized the possibility of taking advantage of them. The interactions among species are life’s gravity, predictable and weighty. Beginning in the layers of earth in which Tim White was digging, or perhaps slightly more recently, these interactions would begin to change. For the first time in the entire history of life, our lineage began to distance itself from other species on which it had once depended. This change would make us human. We were not the first species to use tools or to have big brains. We were not even the first species to be able to use language. But once we had big brains, language, culture, and tools, we were the first species that set out to systematically (and at least partially consciously) change the biological world. We favored some species over others and did so each place we raised a home or planted a field. Anthropologists have been arguing for a hundred years about what makes a modern human, but the answer is unambiguous. We are human because we chose to try to take control. We became human when the earth and all of its living things began to look like wet clay, when our hands, meaty with flesh, began to look like tools.

  When five years had passed and Tim White still had not published any more results from his find, rumors circulated that he had gone a little mad. One can imagine the scenario. After piecing together thousands of bones, White could have easily become obsessed with going back to find those last missing pieces out in the sand. So White might have dug and dug until he spent his life out in the desert, in a hole. Then, in 2009, Tim White came out of his hole and submitted, along with his tribe of colleagues, eleven separate papers to the prestigious scientific journal Science, all of which were published. In the papers, White and his colleagues introduced the young female Ardipithecus ramidus they called Ardi. To White, it was as if he had made Ardi and her kin. She stood at about four feet. Her nose was flat, and in the reconstruction, she gazes permanently ahead. Her fingers are long and her big toe sticks out to the side like a thumb. She was not quite beautiful and yet to White she was lovely.

  When the results were published, Ardi was on the front pages of newspapers around the world, always looking out wide-eyed, as if she had just been surprised. White may or may not have been immortalized, but Ardi was. National Geographic prepared a full-color series on her. She is the new Lucy, though both older and, at least in White’s telling, more significant. Her body seemed to be an ancestor of our lineage or at the very least close kin, and she is unlike anything else that has ever been found. She seems to have traits, splayed toes for example, for walking four-legged among trees, and other traits for walking two-legged on the ground, although even that much is speculative. What is not speculative is that these bones are the most complete reconstruction of an early humanlike creature.

  Nor are her circumstances debatable. She was found among other bones and evidence that, when
pieced together, clearly show that she and her kin were living in a damp, tropical woodland, not a desert. Based on the animal bones and other evidence found around her, there would have been antelopes, monkeys, and palm trees. Ardi’s bones indicate that they were nourished on figs and other fruits and nuts, but also some meat, both of insects and other animals. She would have once stood on a branch not far from where White found her, nibbling at figs and perhaps even wondering about her place in the broader scheme of things.* She used sticks as tools to help her eat when she was hungry, but she had no fire, no stone tools. She had not yet tried to take control of the land. She was like the other species, still wild, still covered in microbes and worms, and still more likely to die in a large cat’s mouth than of old age.

  With White’s publications, Ardi went from unknown to famous in a remarkably short time. It is unknown where Ardi’s reassembled remains will end up. In the standard arrangement, she would be placed in the lineup of our ancestors, the one that starts out with a microbe or a fish and then culminates with a man typing on a computer. In such an arrangement, Ardi would be presented looking forward. Given, though, that she was found with her bones pointed in many directions, it isn’t any more right or wrong to think of her as lying on top of her own (and our) long history and looking up from that point of view. She would stare up at the shallow sand above her. In those few feet of dirty history modern humans evolved. As they did, the enduring presence of parasites, pathogens, predators, and mutualists was about to change, for the very first time.

  Initially, the layers of sediment and bone laid down over Ardi’s body were essentially unchanged from the one in which she was born and died. The forests persisted for generations, replete with monkeys and palms. It took 2 million years for big changes to happen. By the time the grains of those years had fallen over Ardi, the first tools were being made by our ancestors, perhaps her descendants. They were crude—pounding rocks, sharp-edged stones, scrapers, and diggers—but useful and used. Ardi was a million years deep before the next stage began. It was a stage during which hominids such as Homo erectus, who used these crude tools, would give way to those who used hand axes—larger blades with a tear-drop shape—to chop up bodies, though perhaps still not yet to kill them. Amazingly, six more inches of sand would accumulate, 500,000 years, before anything really changed. Across these generations, hand axes were made a 100,000 times in as many places, nearly always in exactly the same way.

  Two hundred thousand years ago, with just an inch or so of sand left to accumulate before the modern age, Neanderthals and early humans began to tie their stones to sticks. Tying stones to sticks was brilliant, at least from the perspective of our ability to kill other animals. When you had to run up to a lion and hit it with a hand ax, the odds were stacked against success. But with a stick attached to that sharp rock, the odds looked at least a little bit better. One imagines that there was, when our ancestors first figured out how to tie sticks to rocks, a high demand for long sticks. These tools were clumsy but served their purpose. With them, we began to kill animals, many of them. Their bones piled up in our early caves, but we had not yet caused the extinction of any other species. We were still just one species among many, although starting to get some attitude and starting to see, perhaps, the possibility of getting some more.

  Twenty-eight thousand years ago, all that was left to lay down was a layer of sand and sediment as thin as powdered sugar. In that sprinkling of time would come everything else that has happened to us—you, me, and the rest of humans. If we want to look for what makes us different as humans, it comes in this slice of time during which Neanderthals, that last holdout of what were once many species of hominids, went extinct. Twenty-eight thousand years ago, we found religion. Stone beads start to accumulate in the sediment, as do grave sites. Statues of women with big butts and breasts become all the rage, early evidence that old preferences have a way of repeating themselves, or perhaps they never go away. We developed a more “sophisticated” culture, and as we did, we began to take control of the land. The moment that made us human in that series of happenings was not the language, the gods, or even the ability to draw Rubenesque women in stone. It was when we decided that when a leopard stalked the cave, we ought to go after it and kill it. When we decided to kill a species not for food or in self-defense, but instead in order to control what lived and did not live around us, when we did that, we were then fully human.

  The extent to which we have changed the earth around us in the meager years we have been a species is astounding, but may have been inevitable, a consequence of our attempts, however bumbling, to survive. The ability to kill animals with pointy stones and sticks changed us, as did fire. We burned to cook. We burned millions of acres, but crudely. We burned forests and grasslands without particular preference. We burned what would ignite, when we pleased. The abilities to build our own dwellings, kill large animals, and transform landscapes with fire combined with a peripatetic urge that would come to transform not just parts of tropical Africa and Asia, but the world. Humans arrived in Australia roughly 50,000 years ago, and not long after, all the biggest animals went extinct. Humans arrived in the New World 20,000 to 13,000 years ago, and with their arrival, mastodons, mammoths, dire wolves, saber-toothed tigers, and more than seventy other large mammal species went extinct.

  The extinctions of the megafauna of Australia and the Americas were hardly the end of the story. As our populations grew denser, we outstripped the ability of the land to provide for us through meat, nuts, and fruit alone. What had long been a kind of informal planting of favorite things became more formal. We tamed plants and then also wild beasts, cows, pigs, goats, and more. Farming arose and spread. With farming, our lifestyles transformed and our impacts magnified. We burned lands to make them clear for farming. We killed the wild animals that might compete with our cows and goats.

  In addition to all of our many intentional effects, we also wrought unintended effects. Among them were those brought about by the species we carried with us from place to place. Some of those species—pigs and goats and chickens—were things we brought, like fire, to make each new place more like the last one. Others species were accidental, stowaways that were either invisible or sneaky. Rats moved with us, as did flies. Species that could not live with us went extinct. Spared were only those species resistant to our spears and fire, and then some of those species went extinct owing to the rats, pigs, goats, or one of the other species we were moving around.

  After each of these changes, we made the world different from what it had been. We did so by making simple changes that favored whole habitats and suites of species that our eyes perceived as good, and disfavoring species we thought were bad. In essence, we created a few new kinds of habitats that we then re-created wherever we went. All of this continued at increasing rates, as populations expanded and our ability to invent new tools increased. Bigger guns let us kill more things faster. DDT let us kill pests from planes. Antibiotics let us kill bacteria. This killing became more necessary as we changed our landscapes. Without it, diseases had become rampant in our new, more populous centers. Without it, pests had grown thick on our monocultures of food. Without the killing, everything we have achieved would revert to the entangled bank we started in, and so we kneel and spray.

  Forty years ago, when people wrote about Lucy, they described her lifestyle as primitive. Now, further into our experiment as modern humans, when one looks at Ardi and her lifestyle (or for that matter Lucy) it is hard not to use the word “idyllic,” perhaps as a function of a change in perspective about our own “success.” Four million years ago, life in Aramis, Ethiopia, was, of course, not idyllic. Yet elements of Ardi’s simple, besieged life can seem, if not good, whole, as though they fit together, each piece of her ecological puzzle connected with its counterpiece. Ardi lived as animals have always lived, with parasites, predators, and little control of the rest of nature. She picked at fleas and dreamed of the leopard’s footsteps. We live today in vas
t areas rebuilt by our own hands to exclude predators, to grow our few grasses (wheat, corn, rye) instead of forests; areas where pests, parasites, and pathogens are cleaned away. We have lived like this for just a tiny slice of history, a scratch of footprints in the loosest sand. In living this way, one can see us from two perspectives. From a great distance, we still look tiny before the magnitude of nature. Up close though, one sees something of the opposite. We have exerted incredible control over nature. We have warmed the entire earth, even as it rotates and circles the sun. We have tried to take control in order to improve our lot, but that control has brought us to a relationship with the rest of the living world far different from that which any species has ever lived.

  Right now, you are at almost no risk of predation. No tigers lurk in your kitchen or yard. You are at a low risk of encountering a parasite. But you are also likely to struggle to see, around you in your life, anything resembling a wilderness devoid of the impact of humans. These realities have consequences, more than we have realized. You might call them side effects, except that they seem to be right in front of us, knocking on our door. They are the ghosts of our ecological history. They knock softly but carry the weight of life’s billions of years.