Why Language Is All Thumbs

March 14, 2008 by Chip Walter

Toolmaking not only resulted in tools, but also the reconfiguration of our brains so they comprehended the world on the same terms as our toolmaking hands interacted with it. With mirror neurons, something entirely new entered the world: memes–a far more effective and speedy method for pooling knowledge and passing it around than the old genetic way.

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


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.

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.

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


See Also:

by Ray Kurzweil

The late Stephen Jay Gould wrote that “the most important scientific revolutions all include, as their only common feature, the dethronement of human arrogance from one pedestal after another of previous convictions about our centrality in the cosmos.” For example, a few centuries ago we thought that all the celestial bodies revolved around the Earth, only to discover that we live on a small planet revolving around a humble star on a remote wing of a routine galaxy. Not so long ago, we thought that we had descended from the gods, only to discover that we had actually descended from primates, and before that worms. Gould, Richard Dawkins, and others point out that evolution works by chance, and if we were to rerun evolution, we would probably look very different, or not have evolved at all.

All of this is true, but it misses the point. We are central after all. Let me explain why.

We live in a universe that is capable of embodying information in atomic and molecular structures. Why this is the case is itself an interesting question. How did it come to be that the laws of physics and several dozen constants embodied in those laws are so precisely what they need to be to allow structures such as atoms and molecules to exist? One interpretation of what has become known as the “anthropic principle” basically says that if we didn’t live in such a universe, we wouldn’t be here talking about it. Another school of thought not inconsistent with the anthropic principle—one that I’ve written about—is that our universe evolved these rules through a series of universes.

Be that as it may, we are fortunate that the laws of physics do allow atoms and molecules to exist, because a large chaotic system filled with such information-rich structures is the perfect stage for an evolutionary process to take place. This has allowed evolution to create structures that over time have become ever more complex, more knowledgeable, more intelligent, more creative, and more beautiful.

If we examine evolution in more detail, we can consider its past and future to comprise six grand epochs, where each epoch is characterized by the mechanism for storing information. The first epoch, which we can call the “epoch of physics and chemistry,” embodied information in atomic and chemical structures. Particularly notable in this regard has been the carbon atom. As a result of its proclivity to make connections with other atoms in four different directions, it is especially good at encoding information.

Ultimately, increasingly complex biochemicals evolved into DNA, a molecule that can directly encode digital data as little software programs called genes. With DNA, evolution had an information processing backbone to keep track of and to guide its experiments. Thus the second epoch, the “epoch of biology,” encoded information in rungs of DNA. Biological machines at the nanoscale, such as the ribosome, turn this DNA data into three-dimensional proteins, which self-assemble into organisms.

As the organisms fought (and in some cases, cooperated with) each other, they evolved to become ever more complex. Ultimately, brains evolved, initiating the third epoch, what I call the “epoch of brains,” with information now encoded in neural patterns of neurotransmitters and ion channels.

When brains evolved to reach a certain level of complexity and capability, and related features of bodies also evolved, the technology-creating species evolved (actually there were a few such species, but only one survives today). This represented the fourth epoch, with information now stored in hardware, and ultimately software designs.

The fifth epoch, which we are now initiating, is when the technologycreating species (that’s us) uses its technology to understand (that is, to reverse-engineer) its own biology, including the methods of its brains, and incorporates the design ideas borrowed from biology into its own technology.

To explain the sixth epoch requires insight into the exponential nature of an evolutionary process. Evolution works through indirection: it creates a capability and then incorporates that capability when it evolves subsequent stages. For this reason, the process accelerates, and the products of the evolutionary process grow exponentially in capability.

For example, it took a billion years for DNA to evolve, but then biology used DNA in all of its subsequent stages. The next stage, the Cambrian Explosion, when all the body plans of the animals evolved, progressed a hundred times faster, taking only about ten million years. The process continued to accelerate, and our species evolved in only a few hundred thousand years. The first stages of technology—fire, stone tools, the wheel—were faster yet, taking only tens of thousands of years. We have consistently used the latest generation of technology to create the next. So today, paradigm shifts in technology take only a few years. Think back to the time most people did not use search engines. That sounds like ancient history, but that was less than a decade ago.

The exponential growth of the capability of technology represents a formidable pace of advancement. The computer in your fifty-dollar cell phone today is a thousand times more powerful than all of the computation shared by all of the students and professors at MIT when I was a student there in the late 1960s. That represents a billion-fold increase in price-performance, but it will pale compared to what we will see in the future. We are now doubling the price-performance of computation and communication every year. And even that rate is increasing over time, so we will see another billion-fold increase in only twenty-five years. During that same period, we will complete the reverse-engineering of the human brain, as that undertaking is also proceeding at an exponential pace. Already, two dozen regions of the human brain, including portions of the auditory cortex, visual cortex, and cerebellum (where we do our skill formation), have been modeled and simulated on a computer. And a simulation of the all-important cerebral cortex is also already under way.

This exponential progression will lead us to saturate the ability to support sublimely intelligent computational processes here on Earth within a century. We will then expand out to the rest of the universe to keep the exponential progression of this evolutionary process going. This expansion beyond the Earth will represent the sixth epoch, which I call “the universe waking up.” The sixth epoch involves vastly expanded human intelligence (predominantly nonbiological) spreading outward from the Earth ultimately at the fastest physical speed possible. We understand this limit to be the speed of light but there are hints that there may be shortcuts in the form of wormholes.

So in a nutshell, that’s the story of evolution past, present, and future. And the key step in this story is a recursive (self-repeating) one. The pivotal point came when a species (Homo sapiens) evolved that was actually capable of initiating an entirely new evolutionary process—technology. Like biological evolution, technological evolution has seen a progression of increasingly complex and subtle forms, but at a pace that is a thousand times faster. That pace, in fact, is continuing to accelerate and will ultimately be millions of times faster, leaving biology in the dust.

So how did this come to be? That is what Chip Walter’s brilliant book explains. It is an important story, not just from the viewpoint of understanding who we are, but from the perspective of the six epochs; it is the story of the tipping point of evolution.

Even if you believe that we are not alone in the universe and that there are many other intelligent technology-creating civilizations beyond the Earth (there are actually good reasons to doubt that, which I won’t go into here), some comparable enabling factors would have undoubtedly occurred in the evolution of these extraterrestrial species. The details would be somewhat different, but the key factors are likely to be similar.

So what were these enabling factors? As Chip explains in the book, the highlights are that we evolved a larger skull to incorporate a larger brain (at the expense of a weaker jaw, so don’t get into a biting contest with another primate). More of that brain was devoted to the cerebral (prefrontal) cortex, so we gained the ability to do recursive thinking. We became capable of assigning a symbol to a complicated set of ideas and then using that symbol in yet more elaborate structures of ideas. This enabled us to devise complicated procedures for creating tools, and to handle the recursive structures in language.

And of course we have that all-important opposable appendage (the thumb) that enabled us to take the “what if ” experiments in our minds and actually try them out. We were able to imagine tying a stone to a stick and then actually build the tool. One might point out that a chimpanzee’s hand looks similar to ours. But the devil is in the details, and a chimp’s hand is just not designed well enough to fashion tools. Some people maintain that chimpanzees are also a tool-making species, and, yes, a chimp can grab a stick and poke it into the ground, but its ability to do this is too clumsy to enable a sustainable process of technology improvement. The pivot points in a chimp’s hands are not in the right place for a power grip or for fine motor coordination. Homo sapiens, on the other hand, were capable of carefully winding the twine around the stone and the stick to create a useful tool, and then using that tool to create the next generation of tools.

Chip points out that our hands would not have evolved as they did if we had to continue to use our front limbs for walking. Moreover, if we had continued to walk on all fours, our hands would not have been free to build tools. So the evolution of our big toes and other anatomical details of our feet was also critical to this tipping point in evolution.

As this book points out, laughing and crying are more subtle but nonetheless equally important developments in the human story. Aside from making life a lot more interesting, they have played a fundamental role in our cultural and technological evolution by being key enablers of social bonding. The brains and hands of a single human are not sufficient to create the grand enterprise of technology. Building the railroads and the communication networks that humanity has assembled has also required a great deal of social organization. Laughing and crying represent key attributes of our ability to put ourselves in another’s place, which was crucial in building our social institutions from families to nations. And let’s not forget kissing, another unique human attribute that contributes to the social order.

There are neural correlates of our social bonding, such as the mirror neurons, which, as the name suggests, enable us to see ourselves through the eyes of others. Recently, we have discovered a set of uniquely complex neurons called spindle cells, which appear to enable our higher emotions. Certain primates such as apes also have spindle cells, although not as many as humans, and recently we have found that whales have them as well.

There is a lot more to this story, and Thumbs, Toes, and Tears is the first book that I am aware of that tells it in a comprehensive—and highly entertaining—way. One could argue that it is the most important story in the history of the universe.

It was bound to happen sooner or later that a species would evolve somewhere in the universe that would combine the ability to do recursive thinking with the ability to manipulate and change its environment. Whether or not this threshold has been reached somewhere else in the universe, we do know that it has occurred here on Earth. As a result, we are the only species (that we know about) that has an exponentially expanding knowledge base that we pass down from generation to generation. We are the only species capable of going beyond its biological limitations through its own designs. We are the only species that has changed its environment and even its own design. We didn’t stay on the ground. We didn’t stay on the planet. And we have not stayed within our biological limitations. A thousand years ago, human life expectancy was just twenty-five years. It was thirty-seven in 1800, and is pushing eighty today. This increase will soon go into high gear as the information technologies to modify biology go into high gear. And along with radical life extension will also come radical life expansion, as we merge with the increasingly powerful and refined technology that we are creating.

And, so, we are unique after all.