Thumbs, Toes, and Tears

  Contents

  Prologue

  I. Toes

  Chapter 1 The Curious Tale of the Hallux Magnus

  Chapter 2 Standing Up: Sex and the Single Hominid

  II. Thumbs

  Chapter 3 Mothers of Invention

  Chapter 4 Homo hallucinator —the Dream Animal

  III. Pharynx

  Chapter 5 Making Thoughts Out of Thin Air

  Chapter 6 I Am Me: The Rise of Consciousness

  Chapter 7 Words, Grooming, and the Opposite Sex

  IV. Laughter

  Chapter 8 Howls, Hoots, and Calls

  V. Tears

  Chapter 9 The Creature That Weeps

  VI. Kissing

  Chapter 10 The Language of Lips

  Epilogue Cyber sapiens: The Human Race, Version 2.0

  Acknowledgments

  Footnotes

  Notes

  Bibliography

  About the Author

  This book is dedicated to my parents,

  Bill and Rosemary,

  who never once told me to stop asking “why.”

  C.W.

  Prologue

  We are—all of us—freaks of nature. We don’t generally see ourselves this way, of course. After all, being human, what could be more ordinary than a human being? But it turns out that our personal (and biased) impressions that we are unremarkable simply don’t stand up against the plain, objective facts. The way we walk, for example, teetering on long, paired stilts of articulated bone, is unique among mammals, and as preposterous in its way as elephant trunks and platypus feet. We also communicate by tossing oddly intricate noises at one another, which somehow carry complex packages of feeling, thought, and information. We share and understand these sounds as if they were scents drifting on the wind, and our minds special noses that sniff the fragrance of their meaning. Using them we are able to change one another’s minds, even bring one another to tears. We also invent, to the point of being dangerous, incessantly bending the things, living and otherwise, around us to our own ends. Because of this habit, we have, for better or worse, created national economies, erected the pyramids of Giza and Chichén Itzá, fashioned exquisite art, sculpture, and music, invented the steam engine, moon rockets, the digital computer, stealth bombers, and “weaponized” diseases. Nothing on the planet seems to escape our urge to remake it. These days we are even tailoring genes to remake ourselves.

  This book is about how we became the strange creatures we are, and why we do these peculiarly human things. It wonders what makes us cry, why we fall in love, invent, deceive, laugh uproariously with close friends, and kiss the ones we care about. It asks what evolutionary twists and turns set in motion events that made the symphonies of Mozart, the insights and art of Leonardo, the drama, humor, and poetry of Shakespeare possible, not to mention bad soap operas, Hollywood movies, and London musicals. It speculates on why chimpanzees, despite sharing so much of our DNA, do not reflect upon the meaning of life, or if they do, why they haven’t so far shared their insights. In the end it wonders how you became you and how our species became, of all the species it could have become, the thoroughly unprecedented one it is.

  Human beings are insatiably curious, especially when it comes to the subject of ourselves. This is not a new insight. Philosophers, poets, theologians, and scientists from Plato to Darwin, St. Augustine to Freud have already penned volumes about our humanness that bow endless rows of the sturdiest library shelves. You might ask, if these thinkers have fallen gasping to the mat trying to wrestle these questions into submission, why this book should have any better luck. The simple answer is that today we have far more solid information to work with.

  During the past decade enormous strides have been made in two broad scientific fields: genetics and neurobiology. Advances in genetics are helping us gain insights into the way all living things evolve and develop. Each of us has come to exist in the unique form we do because of the combinations of genes that our parents passed along. You are, to a large degree, the person you are because of the messages these genes sent, and continue to send, to the ten thousand trillion cells that have assembled just so to form you.1 Hardly a day goes by without some news about a remarkable discovery that further illuminates the molecular machinery of the DNA that makes life possible.

  The other field is brain research. Being a human being (as opposed to a wasp or a fruit fly), all of your behaviors and actions are not dictated by your genes alone. Your brain holds many of the secrets that make humans human. Genes may be outrageously complicated, but the human brain makes our genetic code look like the crayon drawings of a four-year-old.2 Though it weighs a mere three pounds, it consists of a hundred billion neurons, each of which is connected in a thousand different ways to the other neurons around it. This means that every waking moment your brain is linked along a hundred trillion separate paths, trafficking in thought and insight, processing great streams of sensory input, running the complex plumbing of your body, generating (but not always resolving) all of your colliding and conflicting emotions, conscious and unconscious. These connections, by one estimate, make your possible states of mind during the course of your life greater than all of the electrons and protons in the universe.3 Given the immensity of this number, you are never likely to think all of the thoughts you are actually capable of thinking, nor feel every possible feeling. Nevertheless, each shining day we give it a try.

  Over the past decade scientists have been developing ways to scan and reveal in increasingly refined detail how our brains are constructed and operate. They are far from resolving its mysteries, but we know much more today about its behavior than we did even a short time ago. Positron Emission Tomography (PET) scanning and fMRI (Functional Magnetic Resonance Imaging) are revealing “movies” of our thoughts, or more precisely the flow of chemicals in the brain as we think and feel. Today we have a far better understanding of how language, laughter, and thought play themselves out in the brain than we did as recently as the turn of the twenty-first century. Right now the resolution of these movies is cellular, but they will soon reveal the brain at a molecular level, making the reading of minds much more than a parlor trick.

  Scientists also keep nibbling away at the mysterious edges of paleoanthropology, psychology, physiology, sociology, and computer science, to mention only a handful, shedding light bit by bit on the special brand of behaviors we call human. In other words, we remain largely unknown to ourselves, but we are making impressive progress.

  …

  How did we become human beings? All living things are unique. The forces that drive evolution make them so, honing each down to the razor edge of itself, providing it with a handful of qualities that distinguish it as the only animal of its kind. The elephant has its trunk. Bombardier beetles manufacture and precisely shoot boiling hot toxic chemicals from their tails. Peregrine falcons have wings that propel them unerringly through the air at seventy miles an hour to their catch. These traits define these creatures and determine the way they act. But what unique traits shape and define us?

  I have whittled it down to six, each unique to our kind: our big toes, our thumbs, our uniquely shaped pharynx and throat, laughter, tears, and kissing. How, you may ask, can something as common as a big toe, as silly as laughter, or as obvious as a thumb, possibly have anything to do with our ability to invent writing, express joy, fall in love, or bring forth the genius of ancestral China? What could they have to say about rockets and radio, symphonies, computer chips, tragedy, or the spellbinding art of the Sistine Chapel? Just this.

  The origin of all these human accomplishments can be traced to these traits, each of which marks a fork in the evolutionary road where we went one way and the rest of the animal kingdom wen
t the other, opening small passageways on the peculiar geography of the human heart and mind, marking trailheads that lead to the tangled outback of what makes us tick.

  Take the knobby big toes we find at the ends of our feet. If they hadn’t begun to straighten and strengthen more than five million years ago our ancestors would never have been able to stand upright, and their front feet would never have been freed to become hands. And if our hands had not been freed we would not have evolved the opposed and specialized thumbs we have, which made the first tools possible.

  Both our toes and thumbs are linked to the third trait—our unusual throats and the uniquely shaped pharynx inside, which enables us to make more precise sounds than any animal. Standing up straightened and elongated our throats so that our voice box dropped. In time that made speech possible, but we also needed a brain that could generate the complex mental constructions that language and speech demand. Because toolmaking required a brain that could manipulate objects, it supplied the neural foundations for logic, syntax, and grammar so that eventually it could not only take objects and arrange them in an orderly manner, it also could conceive ideas for our pharynx to transform into the sound symbols we call words and organize them so they made sense as well.

  A mind capable of language is also a self-aware mind. Consciousness melded our old primal drives with our newly evolved intelligence in entirely unexpected ways that even language couldn’t successfully articulate. This explains the origins of laughter, kissing, and crying. Though we can glimpse their origins in the hoots, calls, and ancient behaviors of our primate cousins, no other species carries these particular arrows in the quivers they use to communicate.

  …

  Some may argue that we cannot possibly be reduced to six of anything. And some may argue that these traits are not unique to us. Kangaroos stand upright, after all. And dogs whimper and whine. And don’t chimpanzees pucker and smack their lips? Yes, but kangaroos hop, they don’t stride; dogs do not cry tears of sorrow or joy or pride. In fact, they don’t cry any tears at all. No other animal does, not even elephants, contrary to some apocryphal stories. And while chimps can be trained to kiss, they do not naturally climb, during their adolescence, into the backseats of Chevrolets, or anything else for that matter, to neck.

  The larger point is that the extraordinary abilities and behaviors that define us—for better or worse—as a species come from somewhere, and if we keep asking, “where, how, why …” enough, we arrive at their roots. The investigation of one illuminates the other, and together, in the peculiar arithmetic of evolution, they eventually add up to the strange, astonishing, and perplexing creatures we are. Maybe the point isn’t so much to pin ourselves beneath the unforgiving glass of a microscope to arrive at definitive and irrefutable answers. We are far too complex a race to be reduced to the sum of so many split hairs. Maybe the important thing is to simply keep asking interesting questions and follow where the answers take us. As it turns out, they take us to some remarkable and fascinating places.

  —Chip Walter

  Pittsburgh, 2006

  I

  Toes

  Chapter 1

  The Curious Tale of the Hallux Magnus

  The upright posture of man was the start of his fateful development.

  —Sigmund Freud

  The story of the human race is exceedingly long and crooked, and it begins in the grasslands of an immense and mysterious continent.

  Standing on the Serengeti plains of East Africa, you can’t help but feel small. Mostly this is because, in the face of so much of the world all around, you become acutely aware of your mortal insignificance. There is no end to the grasslands, scattered shrub, and baobab trees that sweep out to the horizon. Everything—mountains, trees, gorges, clouds—shrinks. Smaller objects, such as lions and wildebeests and zebra, disappear altogether in the heat and the piddling ability of your eyes to pick out details this small.

  The vast plains feel like another world, yet this is home because it was in a place something like this that our kind stumbled into its upright position and began its long journey into the present. And maybe that is why it also feels timeless, as if it has always been there and always will be.

  But Africa’s savannas have not always been here. Six million years ago Africa was a much more tropical place. In fact, the whole world was. Rain forests rose to latitudes as far north as London. Areas that today are dry grasslands, even deserts, were lush, tropical jungles where all varieties of ape species lived an Edenlike existence. It would be another million years before the creatures that would eventually spawn the human race split off from those that later led to chimpanzees and gorillas.1 But in those days the primate lines had not yet diverged and the environment was warm and sheltered; the food plentiful; and predators, relatively speaking, few.

  If the behavior of today’s gorillas and chimpanzees is any indication, troops of primates, perhaps thirty or forty at a time, lived and roamed the forest, knuckle-walking on all fours for short jaunts, and swinging from tree to tree if they wanted to cover more territory with greater speed. Long-armed and bowlegged, their bodies were built for the jungle. Their feet, like their hands, were designed for gripping branches, with four long fingerlike toes and a fifth inner toe that acted like a thumb as they grasped and swayed gracefully from one branch to the next.

  Few fossils of the tree-dwellers who preceded us remain. The moisture and bacteria that make jungles junglelike are not generally kind to bones left behind. But the evidence suggests that like today’s gorillas and chimps, they very likely fashioned no tools and communicated with a limited repertoire of calls, hoots, and grunts.a Occasionally a little chest-banging might have been in order, or some fang-bearing, to clarify a particular point. Whatever the ways they communicated, these apes epitomized animal intelligence. At the time, they were the smartest primates on the planet, even if from our vantage point—had we been there to watch—their day-to-day life would have seemed monumentally simple and completely bereft of civilization. There were no torches or fire. The nights would have been utterly black and unlit except for the ever-changing moon and the brilliant stardust of the Milky Way tossed by the Big Bang across the black blanket of the sky. The world then was devoid of humanity. But humanity was coming.

  …

  Earth is a testy and capricious planet. Continents shift, mountains rise, ocean currents slip directions from north to south or east to west, the land splits and explodes and collides. This geological restlessness is one of the reasons life on Earth is so wild and rampant. Under the pressures of evolution, life remakes itself and finds a place in the fresh niches the planet continually creates. Adaptation begets new species on the one hand, and on the other, wipes out those that can’t adjust.

  Changeable as Earth is, six million years ago it seems to have been particularly restive. Ice caps were forming over the Antarctic. Global temperatures were dropping, and so were sea levels, which blocked oceans’ equatorial currents, first in the eastern Mediterranean, then at Gibraltar, and finally at the Isthmus of Panama, which rose out of a descending ocean between the nascent North and South Americas. The Mediterranean was draining and then refilling and draining again, depending on the whims of ocean currents and Earth’s wandering landmasses. When it emptied, mountains of salt more than a mile high sometimes formed in its basin, only to be leveled again in a subsequent aeon.

  As all of this unfolded on the western flank of the planet, landmasses in the Indian Ocean were riding northward on the backs of enormous tectonic plates. The Indian subcontinent continued to ram into southern Asia as it had done for thirty-five million years, and by then had made its way twelve hundred miles into the body of the continent, shoving up the Tibetan Plateau and the Himalayas ahead of it like plowed snow.

  This shift was also pulling what scientists call “the Indonesian valve” farther north. This valve consisted of islands and landmasses that controlled the flow of billions of tons of water from the North Pacific into the Indi
an Ocean, and acted like a lock-and-dam assembly. But as sea levels descended and the valve’s large islands edged northward, cooler water from the North Pacific began to stream south, refrigerating the African coast. Slowly the continent’s climate changed as chillier winds swept off the Indian Ocean.2 Jungles backtracked and the Sahara began to form where once there had been forests and grasslands.

  These retreats weren’t made rapidly or in neat lines. Scientists have recently found fossilized remnants and isotopes from six-million-year-old vegetation that reveal that regions of Ethiopia south of Egypt were wetter and more forested than previously thought. These were not tropical jungles, but they were not wide-open savannas either. Forests continued to cluster along rivers and cling to mountain valleys, and many remained on the plains for thousands of years before Serengeti-like grasslands began to nudge them completely aside.

  As the plains of East Africa grew cooler and drier, the enormous continent was also breaking apart. Africa and Asia had begun parting ways, creating the Red Sea; the Gulf of Aden; and farther inland, the Great Rift Valley, a geological scar that runs more than three thousand miles from Syria to southern Mozambique. Colossal volcanoes rose and oozed and exploded, spreading lava, smoke, and ash across thousands of square miles. Kilimanjaro, Africa’s tallest mountain, is a particularly dramatic result—hardened layers of lava piled over three and a half miles high, topped by snow and glaciers even though the mountain sits almost precisely on the equator. Elsewhere the earth cracked like a great bone, and as the rift formed it opened massive valleys with walls that rose thousands of feet.

  A timeline of hominid evolution from Sahelanthropus tchadensis more than six million years ago to Homo sapiens. (Patricia Wynne, © Scientific American.)

  For the apes that had been hunkered down peacefully in this part of the world for so long, it must have been a confounding time as the forests shrunk, the air changed, and the ground shifted, literally, beneath their feet. What they couldn’t know was how profoundly these changes would transform the apes themselves.