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

  The Wild Life of Our Bodies

  Predators, Parasites, and

  Partners That Shape Who

  We Are Today

  Rob Dunn

  Dedication

  for Monica, my favorite wild life

  Contents

  Dedication

  Introduction

  Part I: Who We All Used to Be

  1: The Origins of Humans and the Control of Nature

  Part II: Why We Sometimes Need Worms and Whether or Not You Should Rewild Your Gut

  2: When Good Bodies Go Bad (and Why)

  3: The Pronghorn Principle and What Our Guts Flee

  4: The Dirty Realities of What to Do When You Are Sick and Missing Your Worms

  Part III: What Your Appendix Does and How It Has Changed

  5: Several Things the Gut Knows and the Brain Ignores

  6: I Need My Appendix (and So Do My Bacteria)

  Part IV: How We Tried to Tame Cows (and Crops) but Instead They Tamed Us, and Why It Made Some of Us Fat

  7: When Cows and Grass Domesticated Humans

  8: So Who Cares If Your Ancestors Sucked Milk from Aurochsen?

  Part V: How Predators Left Us Scared, Pathos-ridden, and Covered in Goose Bumps

  9: We Were Hunted, Which Is Why All of Us Are Afraid Some of the Time and Some of Us Are Afraid All of the Time

  10: From Flight to Fight

  11: Vermeij’s Law of Evolutionary Consequences and How Snakes Made the World

  12: Choosing Who Lives

  Part VI: The Pathogens That Left Us Hairless and Xenophobic

  13: How Lice and Ticks (and Their Pathogens) Made Us Naked and Gave Us Skin Cancer

  14: How the Pathogens That Made Us Naked Also Made Us Xenophobic, Collectivist, and Disgusted

  Part VII: The Future of Human Nature

  15: The Reluctant Revolutionary of Hope

  Acknowledgments

  Notes

  Index

  About the Author

  Also by Rob Dunn

  Credits

  Copyright

  About the Publisher

  Footnotes

  Introduction

  Some night, when the moon sneaks through your curtains and finds you still awake in bed, look beside you at your companion. (If you are alone, look at yourself.) Look at the fingernails, smooth beside the rougher skin, not unlike claws. Look at the hands, full of bones strung together by strings of tendons. Follow the bones just below the skin of the arm to the elbow and up along the beautiful shoulder to the neck that, at this moment, might seem to be the loveliest thing you have ever encountered. This body, composed of flesh and desires, evolved in the trees in Africa and Asia, where those nails helped cling to a branch to keep from falling to predators on the ground. You find yourself at this moment beside an animal that was, very recently, wild.

  Some days we remember and feel our connection to what came before us. As we watch a chimpanzee on TV and see its gestures, kindnesses, and cruelties, we feel empathy. As we pick up a turtle in the road, we notice its legs, strange eyes, and a body not so unlike ours. We feel it moving in our hands like some deep muscle of life. But most days we are less aware of being part of a broader community of living species. We no longer see ourselves as part of nature.

  Yet our history clings to us, whether we notice or not. In the last several years, dozens of new and separate discoveries by researchers in anthropology, medicine, neurobiology, architecture, and ecology—especially ecology—have made that much clear. The more we distance ourselves from our evolutionary history, the more we seem to feel the pull of uncut strings of our heritage. There are metaphorical or even spiritual ways in which we might ache for the past, but I mean something much more physical. I mean the ache that our bodies feel in being removed from the ecological context in which they existed for millennia. In being separated from the web of life with which we evolved, we are feeling effects, some good, others bad, but nearly all consequential, not just for how but even who we are.

  We take our modern rituals of work and leisure for granted, and yet for nearly every bit of our history we lived outside, naked or nearly so. We sat, when we dared, on branches. We slept in nests made of sticks, mud, and smooth leaves. We roamed and foraged and knew about the landscape that was around us because we had to, because from its colorful fruits and treasures we ate and either lived or did not. In our transition to modern life, one can make long lists of the things our bodies might miss. It was not long ago that we still walked on four legs. Our bodies remain awkward standing straight. We run fast, but not so fast, and we do it by leaning forward toward that older gait. Our backs, as we sit all day, every day, pain us with our four-footed history. And as the eminent scientist Paul Ehrlich, author of The Population Bomb, put it, standing up also made it harder for us to sniff each other. So much for the good old days.

  Biologists and philosophers have pondered for generations the ways in which our modern lives may be disconnected from our pasts, out of synch. We are haunted by this dissonance, as many have acknowledged, but what seems to have been relatively missed is the origin of the ghosts. They arise from changes in the species with which we interact. When you look beside you in bed, you notice no more than one animal (alternative lifestyles and cats notwithstanding). For nearly all of our history, our beds and lives were shared by multitudes. Live in a mud-walled hut in the Amazon, and bats will sleep above you, spiders beside you, the dog and cat not far away, and then there are the insects beating themselves stupid against the dwindling animal-fat flame. Somewhere near you, perhaps hanging in the palm roof, would be the drying herbs of medicine, a cooked and salted monkey hanging on a stick, and whatever else is necessary, all gathered or killed, all local, all touched and held and known by name. In addition, your gut would be filled with intestinal worms, your body covered in multitudes of unnamed microbes, and your lungs occupied by a fungus uniquely your own. Beyond the edge of the village, past the darkness between houses, would be an even wilder nature filled with insects flexing and scraping their parts together in song, trees falling to the ground, bats fighting among the fruit, and then, of course, the predators who walk silently along our paths, waiting to pounce.

  So it is that the biggest difference between our modern human lives and the way we used to live is not the difference of housing styles and convenience (the transition from outhouse to penthouse). It is instead the change in our web of ecological connections. We have gone from lives immersed in nature to lives in which nature appears to have disappeared. Our disconnection from the nature in which we evolved is unprecedented in its extent and in its consequences.

  We may love our new way of living, the bright lights and clean counters, the delicious food and the air-conditioning—at least our conscious brains may. Meanwhile, our bodies continue to act as though they expect to meet our old companions, the species with which they tangled, generation upon generation, for tens of millions of years. Some of the ways we have distanced ourselves from other species are good; I do not miss smallpox. Other changes are neutral. They affect who we are, but not necessarily for the better or the worse. Many changes, though, are clearly bad. In recent years, for example, a new suite of diseases has begun to plague us. Sickle cell anemia; diabetes; autism; allergies; many anxiety disorders; autoimmune diseases; preeclampsia; tooth, jaw, and vision problems; and even heart disease are all becoming more common. More and more, these modern problems seem to be the consequence of changes not in levels of pollution, globaliza
tion, or even health care systems, but instead of changes in the species we interact with. It is not that we have lost particular species as much as that we have tried to remove whole kinds of life—parasites, bacteria, wild nuts and fruits, and predators, to name a few. The loss of intestinal worms seems to be making many of our bodies ill, just as the circuits in our brains that evolved to deal with predators are now causing us to lose our minds. Our conscious brains have led us to clean our lives of the rest of nature, but the rest of our body, from our guts to our immune system, is having second thoughts.

  The researchers studying different aspects of our disconnection from nature are in different fields. They do not tend to talk to one another, yet they have come to parallel conclusions about the extent of the consequences of our disconnection. An immunologist holds up our intestines and sees the consequences of having removed our worms. An evolutionary biologist looks at the appendix and notices what it had been doing in our bodies all along without being noticed. A primatologist looks at the neurons in our brain and sees the vestiges of predators. Psychologists look at our fears of strangers and our wars and see in them a mark, a kind of stigma, of changes in our exposure to disease. Each thinks they have discovered something important. They have—here I attempt to bring these stories together, weaving through them the common reality that our past haunts us. As I do, I try to step back to reveal the elephant in the room, or rather the effects of having removed the elephant from the room, along with worms, microbes, birds, fruit, and the rest of the most readily apparent life.

  We all know about the biodiversity crisis, but the related crises resulting from changes in the kind of nature we interact with is similarly immediate. Whether lying in bed or sitting in front of your computer, when you ache, you ache with the history of your origin. You ache with the context you miss. The savannas and forests of our ancestry are still with you. They come to you, like the pain of a missing limb, when you sneeze, when your back aches, or when you are scared. They even come to you each time you choose what to plant, eat, or buy. This history comes to some more than others, but in one way or another, it comes to us all.

  In the pages that follow, I tell the story of the consequences of our changing relationships with the rest of nature. I begin with our parasites and then discuss, in turn, the species we depend on directly (our mutualists), our predators, and then our diseases. I conclude by considering the crossroads at which we find ourselves. We have options. One, the one we are headed toward, is a world in which our daily lives are more removed from nature (which is itself increasingly impoverished) and we are sicker, less happy, and more anxiety-ridden for it. In this world, we treat our problems with more and more medicines in an attempt to use chemicals to restore what we miss from other species. We live in a bubble from which we look out at the rest of life. The other options are more radical, but no less possible. Through the stories of a handful of half-wild visionaries, I will consider some of these radical options that include giant living buildings, predators in our cities, and the restoration of parasitic worms to our guts’ wild plains.

  In the end, what we need in our daily lives is not quite wilderness. Wilderness is what we did away with to allow ourselves to live free of malaria, dengue, cholera, and large carnivores eating our loved ones. We need a nature managed so as to complement our happy lives, a kind of wildness, perhaps. It is taboo to say that we should manage the nature closest to us for us, but ever since we first started to farm or control pests that is what we have always done. The step we must take now is to manage with more care and nuance. We can favor good bacteria in our mouths, and discourage bad bacteria. We have just chosen not to. We can introduce harmless nematodes into our bodies to restore our immune system. We can expose ourselves to the species in which we find joy, curiosity, and happiness. We can even, more ambitiously, create green cities, cities more revolutionary than just buildings with green rooftops, cities in which entire walls are built out of life. Imagine butterflies emerging from cocoons on flowers growing out of high-rise apartment balconies. Imagine predators diving on prey on street corners—hawks in Manhattan, bears in Fairbanks. Imagine all the species—or if not all of them, more of them—and their wild calls, back outside our doors.

  In the last century, we used antibiotics to kill all of the bacteria in our guts in order to get rid of a single problematic species. It was the century in which we killed all of the insects in our fields in order to control the few pest species. It was the century in which we killed wolves everywhere to save sheep in some places. It was the century in which we scrubbed our counters clean to “get rid of germs.” All these actions saved tremendous numbers of lives but also left us with new more chronic problems and a nature devoid of its richness. We know more now and can act more wisely to create for ourselves more natural and healthier lives. The solution to the problems caused by our “clean living” is not as simple as just playing in the dirt. Our task is to create a new kind of living world around ourselves, one that we interact with in many different ways, a living world that is not just the species that survive deforestation, antibiotics, and disturbance, but instead some more intelligent and lush garden.

  Let our lives again be where the wild things are.

  Part I

  Who We All Used to Be

  1

  The Origins of Humans and the Control of Nature

  In the summer of 1992, Tim White saw the remains that changed his life. The first thing he saw was a tooth, a single molar. And then as he approached the spot in the clay bed, there was more. He could not be sure what he was looking at. They could have been the remains of a dog almost as easily as those of a teenage girl. He could not even be sure whether there was just one body or several. A search party was staged and every bit of potential evidence began to be collected. Soon, a little farther away, other clues were discovered—more teeth, and an arm bone. The flesh was long gone, yet in their precise geography, these parts seemed to tell a story.

  White stepped back from the bones and walked around them to gain perspective. The more he looked, the more he was able to sort out what he was seeing. But it took time. It was not until 1994, two years later, that enough bones turned up to reconstruct the body, or at least more of its parts. Ultimately, several individuals would be discovered, but it was this first one that called to him. All these years removed from her last breath, she still commanded attention. He could scarcely look away. She stirred a feeling in him—maybe it was the heat mixing with his ego, a kind of psychological indigestion—yet he began to imagine it was something else. Every scientist who studies fossils hopes that one day his walk in the desert will be interrupted by a find everyone else missed, a find so important that the desert itself seems to increase in worth. With time, White began to believe that this was what had happened to him.1

  Tim White, a professor of biological anthropology at the University of California, Berkeley, has been working with the bones of human ancestors and other primates for decades. He knows the bones of monkeys, apes, and men as intimately as anyone knows anything. He has run his fingers over millions of bones, drawn them, tapped them, dug them out. Time and intuition suggested to White that these bones in the sand were not quite a woman. Nor were they quite an ape. White could not prove where they belonged on the tree of life, not as they lay disordered in the desert, but he felt in some deep and primitive part of his brain that they were significant. Not the missing link connecting humans and apes, but something more. Perhaps they were the bones that made the entire search for a missing link irrelevant. So much of fossil work has to do with native intuition, sorting the ordinary from the extraordinary upon a quick glance or a feel. White’s gut knew this was extraordinary. The skull was unusual. The feet were unusual. And when White and his colleagues looked at the sediment in which they were found, it was a thin layer sandwiched between two volcanic events, events of known ages, between which played out the life of their quarry, a life whose date of birth was 4.4 million years ago.2 The bones had b
een left there long before the origin of humans or that famous fossil Lucy, on which so much of our existing understanding hinged. If White was right, this find would immortalize him. If he was wrong, well, he might be just one more anthropologist left half mad in the dust of his own imagination.

  Certainly there were things that pointed to White’s madness. The odds of finding a fossil as unique and important as he thought this one might be were extraordinarily low, a billion to one, if not worse. Yet, if White was looking for affirmation, he could also find it. The context of this discovery alone suggested he could be on to something. He and his colleagues were working in Ethiopia’s Afar desert. Their site, called Aramis, was not far from a place where other early-hominid bones had been found in 1974. Nor was it far from where he and colleagues had discovered the very earliest bones of humans, some 160,000 years ancient.3 If White was going to excavate these bones, he wanted to do it right. “Right,” though, is expensive in both time and money. The temptation to do it quickly, to make a surgical but dirty strike, would have been great. He resisted. Credibility in the study of human evolutionary history is hard to come by but easy to lose. What would come next—the many tiny bones and fragments of bones, each one picked from the ground, treated, and pieced together slowly and carefully—would have to be done perfectly. A single fragment of jaw would come to occupy months of an anthropologist’s time. A shard of pelvis, weeks more. And there were just so many bones. It seemed as if this body had been trampled on by ancient hippos, only to be punished a little more each year by the grinding movement of the earth, the tunneling of termites and ants and, more simply and less forgivingly, the passage of time.* These bones had 4.4 million years to fall apart. He hoped it would not take quite that long to put them back together. All of Tim White’s assistants and all of his colleagues struggled. It was not just that the bones had been smashed to pieces. The pieces themselves were brittle. When handled incautiously, they would turn to dust. A few did.