Excerpted from Thumbs, Toes, and Tears, Walker & Co. 2006. Published on KurzweilAI.net March 4, 2008. Reprinted with permission.

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. 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. 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. 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 went 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.

. . .

Why Language Is All Thumbs

From Chapter 3, “Mothers of Invention”

Because we have only two hands, rather than, say, eight tentacles, like an octopus, we manipulate objects in an ordered sequence, not all at once. That means to consciously do “A” before “B” and “B” before “C,” we have to focus. You don’t absentmindedly build a bow, or shape an arrow, or design a steam engine. It requires intention and concentration. Anyone who has struggled with assembling furniture at home knows that if B does not follow after A and C upon B, things have a way of falling apart.

If scientists such as Lakoff, Johnson, and Greenfield are right, we manipulate thoughts the way we do because our hands once learned to shape sticks, stones, and animal skins into tools. Nouns became the equivalents of objects, verbs represented actions, and we (or our hands) took on the role of a sentence’s subject.

To ancestors like Handy Man, the physical grammar of cracking open a femur to eat the marrow inside might have gone something like, “Hit bone (with) stone.” He might not have had any words—any mental symbols—to attach to these objects or actions, but the pattern of using one thing to affect another would have been part of his physical experience. There was no way around it. If you pick up a stone to strike a bone, certain actions must unfold in a certain sequence for the whole business to work out. The brain must consciously conceive and act on that sequence, or the bone and stone will forever sit there, and never the twain shall meet. And any ape that spends his day gazing at a rock and bone, doing nothing, will never eat an ounce of marrow, and certainly won’t live long enough to pass his genes along. Animals like these, as scientists like to say, “get selected out.”

The unavoidable conclusion here is that toolmaking not only resulted in tools, but also in the reconfiguration of our brains so they comprehended the world on the same terms as our toolmaking hands interacted with it. The physical conversation our marionette fingers were having with the objects around us was shaping the way our brain organized and thought about everything. The hand speaks to the brain as surely as the brain speaks to the hand. Art, or at least craft, was beginning to imitate life, and the rudiments of language and complex human thought were sprouting from the sense-able, concrete sequences of that life.

. . .

In 1996, Vittorio Gallese, Giacomo Rizzolatti, and their colleagues at the University of Parma in Italy inadvertently discovered the strange and mysterious ways in which evolution works. They were recording signals transmitted from neurons in an area of the brains of macaque monkeys called the F5 region. This is a specific sector of the frontal lobes that sits among a larger area of the brain that deals with making and anticipating movements called, fittingly, the premotor cortex.

The scientific team already knew that F5 neurons fired when monkeys performed specific goal-oriented tasks with their hands or mouths—picking up a peanut and then holding it, for example. But for this series of tests they wanted to see if the F5 neurons acted any differently when the objects themselves were different. Did it matter, they wondered, if a monkey was picking up a peanut rather than a slice of apple?

It was while they were performing this routine experiment that they noticed something odd. When a macaque watched a researcher’s hand pick up an object and bring it close to his mouth, the sensors connected to the monkey’s brain indicated that neurons in its F5 region were firing. They didn’t activate when the monkeys simply saw the objects sitting there, only—and this was what was so unusual—when the monkey watched researchers pick them up, or when the monkeys themselves picked them up.

The implications of this are enormous. If the same neurons were firing in the monkeys’ brains when they watched the action, it meant they were playing out what they were seeing before them inside their own brain— their mind’s eye—just as if they were doing it themselves. They were mentally “mirroring” the physical action. You could also say that in a rudimentary way they were imagining they were doing the action; reliving, neuron by firing neuron, the experiences of others—in effect, putting themselves in the shoes of the researchers they were watching. They were experiencing a form of empathy that itself required a kind of imagination.

The ignition of F5 neurons made these seemingly simple gestures and maneuvers a form of communication far more powerful than any hoot, grunt, or howl. After all, if the monkey was mentally picturing the actions of the researcher, it was also quite possibly remembering and learning it. Monkey see, monkey do.

If you look hard, you can catch glimpses of early conscious communication on all sides of this. Imagine two habiline creatures—a parent and a child—sitting in their small, lakeside camp two million years ago, smoke billowing from the enormous volcanoes at their backs. They have roughly twice the neuronal wetware of the average chimp today (and certainly more than a macaque monkey), so their intelligence is far from trivial. On the other hand, they still can’t speak, so their ability to share what is on their minds is limited, even though they undoubtedly have far more to communicate than any of the other animals around them.

Now imagine the parent is making a simple tool, like those that Nicholas Toth and his colleagues experimented with. The child watches intently. Simply by observing, the same neurons—her mirror neurons—are firing in her head that are firing in her parent’s. And so when she attempts to repeat the action she has been watching, she can call upon those fired neurons to guide her hands to do something she has never actually done before but has imagined doing.

For his part, when the parent strikes flint against the rock, he is silently talking to the watching child. He is saying, with his hands, “This is how you make this thing. You hold this large rock like this and strike it with this small rock just so.” You can see him holding up the sharp sliver of flint that the blow has created. “See, now you have a knife.” And then next, he may carve the skin off a carcass, taking the “conversation” in a new direction.

The entire time the child is “listening.” Neither parent nor daughter have any language; not a single word they can exchange, not even a concept of words, only the looks on their faces, the expressions in their eyes, the gestures they make with their hands as they manipulate and exchange the rocks and flint. But a lot of information is traveling back and forth between their two minds. In a very real sense they are conversing.

This apparent connection between conversation and manipulation is more than metaphorical. More recent research, built on Gallese’s and Rizzolatti’s original discovery, has revealed that the F5 region in macaque monkeys is an analog for areas in our own brain essential for generating human language and speech (not necessarily the same thing, as we shall see). We know this partly because a few years after the discovery of mirror neurons, Rizzolatti and another researcher, Scott Grafton, found that when humans watch someone handle objects, a region of the brain called the superior temporal sulcus, which sits directly behind the left temple, activates and mirrors what they see. This surprised scientists because they had long thought that this part of the brain existed primarily to send the signals to Broca’s area that generate speech. Now it appeared Broca’s area was handling other jobs as well, or deeper ones. It not only sent signals to the muscles that generated speech, it sent the signals to hands and arms that enabled the precise manipulation of objects.

Rizzolatti thinks this fusion of objects and imagination, gestures and words provides a glimpse into the genesis of language. Mirror neurons might be the primal wetware that enabled our ancestors to transform the common ground of doing and making into the earliest forms of conscious communication. F5, or something like it, might very well have been the bud from which Broca’s area—a cornerstone of human language—blossomed.

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The Insights of Dr. Broca

How we actually generate language is a mystery, but we know that we can’t do it if a part of the brain known as Broca’s area, named for the brilliant French doctor and anatomist Pierre Paul Broca, who discovered it, doesn’t function properly. Broca first located this part of the brain when he performed an autopsy in 1861 on a patient, known as Tan, who had died from gangrene. The man was known as Tan because when he tried to speak all he seemed capable of saying again and again was the word “tan.” This affliction became known as Broca’s aphasia, and the autopsy revealed that there had been damage to specific sections of the inferior frontal gyrus in the left frontal lobe of the brain (roughly near the left temple). Subsequent studies Broca and others performed confirmed that in most people (left-handers usually being the exception) this is the area of the brain that somehow takes the symbols our minds create when we want to communicate, attaches sounds to them, and then coordinates sending the signals to all of the muscles needed to make the precise sounds we call speech (or in the case of those who can’t speak, make the hand signals needed to communicate).

Brain scanning technology has confirmed Broca’s findings. These areas of the brain “light up” when we generate speech. Broca’s area is connected to Wernicke’s area by a neural pathway called the arcuate fasciculus, and using these two sectors of the brain, we handle most of the generation and understanding of the spoken (or signed) word. Because Broca’s area is so closely located next to areas of the brain associated with mirror neurons and those sectors that control both facial muscles and hand coordination, it may help explain how toolmaking, gestures, and speech are connected.

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With mirror neurons, something entirely new had entered the world: a far more effective and speedy method for pooling knowledge and passing it around than the old genetic way. Ideas could now be shared between minds! And that sort of knowledge-pooling, as Darwin observed, would have seriously improved the chances of a troop’s, a family’s, or an individual’s survival. As he put it, “the plainest self-interest, without the assistance of much reasoning power, would prompt the other members [of a tribe] to imitate him; and all would thus profit. … If the invention were an important one, the tribe would increase in number, spread and supplant other tribes.”

This means that two astounding advances were unfolding during Homo habilis’ brief stay on Earth. First, entirely new knowledge was being intentionally generated out of the brain of a single creature. Toolmaking marked the birth of invention. Second, knowledge could now be duplicated and relocated to other minds; it was no longer doomed to die with the brain that conceived it. Just as the evolution of DNA made it possible for a gene to be copied and shared from one generation to the next, mirror neurons, and the new behaviors they made possible, meant that an idea—a “meme,” as Richard Dawkins has put it—could be copied and passed along from one mind to the next. Conscious communication had emerged, even if only in an embryonic form, and in its wake everything from gossip to oratory, mathematics to the laws of Hammurabi, stand-up comedy to the computer code that sends probes to the moons of Saturn would follow. We were building the scaffolding for true human behavior, relationships, and, ultimately, that most monumental of all human inventions: culture.

But how would our ancestors even begin to cross the chasm that yawned between the first flint knives and the great edifices of human endeavor we have erected since?

© 2006 Chip Walter