Early this morning, even before you were out of bed, your hands and arms came to life, goading your weak and helpless body into the new day. Perhaps your day began with a lunge at the snooze bar on the bedside radio, or a roundhouse swing at the alarm clock. As the shock of coming awake subsided, you probably flapped the numb, tingling arm you had been sleeping on, scratched yourself, and maybe even rubbed or hugged someone next to you.
After tugging at the covers and sheets and rolling yourself into a more comfortable position, you realized that you really did have to get out of bed. Next came the whole circus routine of noisy bathroom antics: the twisting of faucet handles, opening and closing of cabinet and shower doors, putting the toilet seat back where it belongs. There were slippery things to play with: soap, brushes, tubes, and little jars with caps and lids to twist or flip open. If you shaved, there was a razor to steer around the nose and over the chin; if you put on makeup, there were pencils, brushes, and tubes to bring color to eyelids, cheeks, and lips.
Each morning begins with a ritual dash through our own private obstacle course--objects to be opened or closed, lifted or pushed, twisted or turned, pulled, twiddled, or tied, and some sort of breakfast to be peeled or unwrapped, toasted, brewed, boiled, or fried. The hands move so ably over this terrain that we think nothing of the accomplishment. Whatever your own particular early-morning routine happens to be, it is nothing short of a virtuoso display of highly choreographed manual skill.
Where would we be without our hands? Our lives are so full of commonplace experience in which the hands are so skillfully and silently involved that we rarely consider how dependent upon them we actually are. We notice our hands when we are washing them, when our fingernails need to be trimmed, or when little brown spots and wrinkles crop up and begin to annoy us. We also pay attention to a hand that hurts or has been injured.
The book you are holding is a meditation on the human hand, born of nearly two decades of personal and professional experiences that caused me to want to know more about the hand. Among these, two had the greatest impact: first, as an adult musical novice, I tried to learn how to play the piano; second, as an experienced neurologist, I began to see patients who were having difficulty using their hands. Each experience afforded its own indelible lessons; each spawned its own progeny of questions.
Like most people, I have spent the better part of my life oblivious to the workings of my own hands. My first extended attempt to master a specific manual skill for its own sake took place at the piano. I was in my early forties at the time and in my dual role as parent and neurologist had become enchanted by the pianistic flights of my twelve-year-old daughter, Suzanna. "How does she make her fingers go so fast?" was the question that occurred to me when I interrupted my listening long enough to watch her play. I read everything I could about the subject and finally realized I would never find the answer until I took myself to the piano to find out.
As a beginning student I imagined that music learning would go just as it is depicted by music teachers: begin with simple pieces, learn the names of the notes, practice scales and exercises, memorize, play in student recitals, then move on (shakily or steadily) to more and more difficult music. But over the course of five years of study my personal experience deviated further and further from this itinerary. It was not that I was fast or slow, musical or unmusical; at various times I was each of those. Despite the guidance of a seasoned teacher armed with the highly polished canons of music pedagogy, the whole enterprise was rife with unexpected turns, detours, and diversions. Inside me, it seems, there was already a plan for being a musician--a modest one, but a plan nonetheless: the protocols of music had simply set the specific cognitive, motor, emotional, and social terms according to which hand and finger movements that were initially unsure and clumsy would gradually become more accurate and fluent. As I hope to demonstrate--even to the satisfaction of music teachers--I might as easily have been in a woodcarving class, or learning how to arrange flowers or build racing-car engines.
After several years of piano study I began to see musicians as patients. Most came expecting that a doctor with musical training would better understand their physical problems than one without such experience. Later, the "hand cases" also came from restaurants, banks, police stations, dental offices, machine shops, beauty parlors, hospitals, ranches. All came for the same simple reason: they could not do their jobs without a working pair of hands.
A major turning point in my thinking about the hand came as the result of a presentation I made to a group of musicians about a particularly difficult and puzzling problem called musician's cramp. I had brought along a video clip to show during the talk. It was a brief clinical-musical medley of hands that had either been injured or had mysteriously lost their former skill; formerly graceful, lithe, dazzlingly fast hands could barely limp through the notes they sought to draw out of pianos, guitars, flutes, and violins. Just a few minutes after the film began, a guitarist in the audience fainted. I was amazed. This was not the sort of grotesque display one sometimes sees in medical movies; these were just musicians unable to play their instruments. When the same thing happened at subsequent presentations--a second and then a third time--I was genuinely puzzled. I decided I must have missed subtleties or hidden meaning in these films apparent only to very few viewers. It was not until much later that I came to understand the real message these fainting musicians were expressing.
I now understand that I had failed to appreciate how the commitment to a career in music differs from even the most serious amateur interest. Although I had worked very hard as a beginning piano student, took the work seriously and spent a great deal of time at it, it was not my life. Consequently I did not anticipate the profound empathy for the injured musicians that would be felt by some viewers of these films. Moreover--and this is a lesson I learned, one person at a time, as I conducted interviews with nonmusicians for this book--when personal desire prompts anyone to learn to do something well with the hands, an extremely complicated process is initiated that endows the work with a powerful emotional charge. People are changed, significantly and irreversibly it seems, when movement, thought, and feeling fuse during the active, long-term pursuit of personal goals.
Serious musicians are emotional about their work not simply because they are committed to it, nor because their work demands the public expression of emotion. The musicians' concern for their hands is a byproduct of the intense striving through which they turn them into the essential physical instrument for realization of their own ideas or the communication of closely held feelings. The same is true of sculptors, woodcarvers, jewelers, jugglers, and surgeons when they are fully immersed in their work. It is more than simple satisfaction or contentedness: musicians, for example, love to work and are miserable when they cannot; they rarely welcome an unscheduled vacation unless it is very brief. How peculiar it is that people who normally permit themselves so little rest from an extreme and, by some standards, unrewarding discipline cannot bear to be disengaged from it. The musician in full flight is an ecstatic creature, and the same person with wings clipped is unexploded dynamite with the fuse lit. The word "passion" describes attachments that are this strong. As I came to learn how such attachments are generated, it became the mission of this book to expose the hidden physical roots of the unique human capacity for passionate and creative work. It is now abundantly clear to me that these roots are more than deep and more than merely ancient. They reach down, and backward in time, past the dawn of human history to the beginning of primate life on this planet.
Paleoanthropology--the study of ancient human origins--has until recently been better known to the public through cartoon images than through its serious work. But this seemingly dryasdust discipline is now followed by an enthralled public because of the stunning discoveries and brilliant reporting of its most prominent modern pioneers, including the Leakey family in Kenya, Donald Johanson, and, of course, Stephen Jay Gould. New information harvested from fossilized skeletal fragments millions of years old has both enlivened evolutionary theory and joined it to the developmental and behavioral sciences, linguistics, and even the neurosciences. Charles Darwin's name and his ideas are again as widely discussed and debated as they were in the middle of the last century. Indeed, the explosion of recent publications about Darwin, neo-Darwinism, universal Darwinism, and even neural Darwinism certify his genius; with the passage of time the impact of his insights and his work simply grows an grows.
Reawakened interest in Darwin finds a quiet but highly significant counterpart in a recent growing awareness of the remarkable life and work of Sir Charles Bell, a Scottish surgeon who was not only a contemporary of Darwin but one of the most respected comparative anatomists of his day. As a young boy, Bell had not only studied drawing but assisted his older brother in the teaching of anatomy. In 1806, having moved from Edinburgh to London and having become an anatomy teacher himself, he published Essays on the Anatomy of Expression in Painting, a book which was popular with both artists and surgeons and which remained in print for over forty years. Bell's work on comparative anatomy was well known to Darwin, and his Essays presaged Darwin's publication, in 1872, of The Expression of the Emotions in Man and Animals.
In 1833, with Darwin near the midpoint of his epic five-year voyage on the Beagle, Bell completed and published the Fourth Bridgewater Treatise: The Hand, Its Mechanism and Vital Endowments, as Evincing Design. In keeping with the terms of the Bridgewater endowment, Bell had intended that his book would help to establish biology as a support for religious faith. But this was not the result. His analyses of the behavioral consequences of variation in anatomic structure, and his insights into the relationship between movement, perception, and learning, were revolutionary and seminal. The book, and Bell's continuing work on the anatomy of the nervous system, had a far greater influence on the development of the science of physiology of the nervous system than on religious thought or polemic.
It is genuinely startling to read Bell's Hand now, because its singular message--that no serious account of human life can ignore the central importance of the human hand--remains as trenchant as when it was first published. This message deserves vigorous renewal as an admonition to cognitive science. Indeed, I would go further: I would argue that any theory of human intelligence which ignores the interdependence of hand and brain function, the historic origins of that relationship, or the impact of that history on developmental dynamics in modern humans, is grossly misleading and sterile.
Following Bell, we will begin with a brief review of what is known of the human (and the hand's) evolutionary timetable, and then move to the present--to the "Decade of the Brain"--to consider the most recent efforts by anthropologists and brain scientists to create a comparable timetable, or track, for the evolution of intelligence. This review is an essential preliminary to a later chapter on human language and a discussion of the role some theorists attribute to the hand in the emergence of symbolic thought.
We will continue with a compact overview of the anatomic and physiologic nuts and bolts pertinent to hand function. It is not possible to understand the hand as a dynamic part of the body, or to safely tackle broader issues concerning the hand in relation to brain function or human development, without at least a minimal grasp of the fundamentals of its physical structure and function. But what do we mean by "the hand"? Should we define it on the basis of its visible physical boundaries? From the perspective of classical surface anatomy, the hand extends from the wrist to the fingertips. But under the skin this boundary is just an abstraction, a pencil line drawn by mapmakers, giving no clue as to what the hand is or how it actually works.
On both sides of the wrist, under a thin layer of skin and connective tissue, pale white, cordlike tendons and nerves pass from the hand into the forearm. Are the tendons above the wrist--that is, in the forearm--part of the hand? After all, we are able to hammer nails or use a pencil only because of the pull of tendons and muscles near the elbow. From the perspective of biomechanical anatomy, the hand is an integral part of the entire arm, in effect a specialized termination of a cranelike structure suspended from the neck and the upper chest. Should we agree that the hand must be conceptualized in biomechanical terms, we invite further complexities of definition. We would know very little about the living actions of the hand except for observations of the effects of injury on its function; such observations are well documented from the time of ancient Greece, when it was known that muscles could be permanently paralyzed by cutting a thin white cord that somehow activates the muscle. Such cords are called nerves, and physicians and anatomists in ancient Alexandria already knew that nerves originated in the spinal cord. What are we to do with this fact? Are the nerves controlling the muscles and tendons that cause the hand to move also part of the hand?
Another set of observations, beginning a little over a century ago, has made it clear that the hand can be rendered useless by damage to the brain from injury (a fall or a gunshot wound) or as the result of a disease process (stroke, multiple sclerosis, or Parkinsonism, for example). Pathologic change associated with specific diseases or injuries, when confined to different parts of the brain, can have quite different and distinctive effects on hand function. Should those parts of the brain that regulate hand function be considered part of the hand? The perspective of physiological or functional anatomy suggests that the answer is yes. We need go no further than this to realize that a precise definition of the hand may be beyond us. Although we understand what is meant conventionally by the simple anatomic term, we can no longer say with certainty where the hand itself, or its control or influence, begins or ends in the body.
The problem of understanding what the hand is becomes infinitely more complicated, and the inquiry far more difficult to contain, if we try to account for differences in the way people use their hands, or if we try to understand how individuals acquire skill in the use of their hands. When we connect the hands to real life, in other words, we confront the open-ended and overlapping worlds of sensorimotor and cognitive function and the endless combinations of speed, strength, and dexterity seen in individual human skill and performance. We also confront the vagaries of human learning. Consider the following sequence of events:
Two people of the same sex and roughly the same age, physical makeup, and education both begin piano lessons and juggling lessons. At the end of one month, the first student seems to be progressing at the piano faster than at juggling, and the second student seems to be doing the opposite, and each reports that her hands seem to have more of a "knack" for the one skill than for the other. In response to these divergent results, piano and juggling lessons are modified for each student, introducing whatever changes seem most likely to equalize skill levels in the two students. However, as time goes on, and despite all efforts at remediation, the differences in performance increase. No matter what is done, the first student continues to improve faster at the piano than at juggling, and the second still does the opposite.
How can this be? Are there significant but unseen structural differences in the hands of these two individuals? If we knew more about the detailed anatomy and biomechanics of their hands and arms, could we explain the differences in their abilities to refine these special skills? Perhaps. Or should we look to brain science to explain the discrepancy? The answer here is also, at best, perhaps. If it is true that the hand does not merely wave from the end of the wrist, it is equally true that the brain is not a solitary command center, floating free in its cozy cranial cabin. Bodily movement and brain activity are functionally interdependent, and their synergy is so powerfully formulated that no single science or discipline can independently explain human skill or behavior. In fact, it is not clear that what we have asked can be called a scientific question. The hand is so widely represented in the brain, the hand's neurologic and biomechanical elements are so prone to spontaneous interaction and reorganization, and the motivations and efforts which give rise to individual use of the hand are so deeply and widely rooted, that we must admit we are trying to explain a basic imperative of human life.
Ultimately, this "meditation" seeks to juxtapose and integrate three quite different perspectives on the role of the hand in human life:
1. the anthropological and evolutionary perspective: where the human hand came from and how it acquired the repertoire of movements that have given it a central role in human life and survival;
2. the biomechanical and physiological perspective: the engineer's view of the specialized structure and function of a forelimb no longer used for weight-bearing and whose terminal configuration is adapted for control of external objects;
3. the neurobehavioral and developmental perspective: how the dynamic interactions of hand and brain are developed and refined, and how that process relates to the unique character of human thought, growth, and creativity.
The last of these three perspectives is the one that seems to me most in need of illumination.
Early in 1990 I was living in Germany, having taken my interest in performance problems of musicians to a research laboratory at the University of Dusseldorf. My particular interest, as I have mentioned, was in hand cramps, a problem that suggested to my imagination a marionette whose strings had knotted up of their own accord. Since Dusseldorf happens to be the home of a prominent marionette theater, I sought out its director, Anton Bachleitner, to find out how these puppets actually work. Inevitably, our discussion of puppets led to a discussion of his own interest in them. Bachleitner, then in his thirties and a man who had lived since the age of eight in the world of marionettes, insisted that he knew the first day he set eyes on a puppet that he had found his life's work. A master woodcarver, he has designed, carved, and painted almost all the puppets for the shows produced by his company; he personally trains all his players, chooses and adapts the plays, and performs in them as well. Every bit as much as any musician I have known, he lives through his hands.
How could Bachleitner have known when he was eight years old that this was what he would do for the rest of his life? His description of that realization did not seem to be just a young boy's escapist fantasy; he knew what he wanted to do with his life, he acted on that knowledge immediately, and he got what he wanted. What could possibly account for his clear, early vision of a future life and the fortuitous mix of aptitudes he would later need? And how can we possibly explain the directness and ingenuity with which he got himself where he knew he belonged?
As I located and interviewed others whose careers depended on unusually refined hand control I found that most could spell out in five minutes the purely procedural demands of their work. But to understand fully how they had incorporated that knowledge and had turned it into a career was another matter. Each had made a succession of discoveries that had been followed by a strengthening of the desire to learn more and a determination to "get it right," or "find the truth," no matter what the obstacles. This process always resulted in a distinctive personalization of their work, and a growing sense of (and demand for) independence. The process usually turned out to have been not unlike my own experience with piano lessons: improvisational--nothing like what was in the books. I also found in these stories a hint of inevitability, as though, like Bachleitner, at least some had known all along where they belonged.
Are people genetically predisposed toward a particular life's work based on a biological aptitude? If so, could genetic makeup predispose certain people toward careers in which refined hand skills are indispensable? If that were true, what would be the implications for our cherished notions of intelligence and aptitude? A deeper question about the nature of "innate talent" also arises, since we are a species evolving genetically at a far slower pace than the world in which we as individuals must survive.
The "design" of the modern human brain was completed 100,000 years ago, perhaps even earlier. Does that mean that each living person is locked into a certain kind of mind as tightly as he or she is locked into bone structure, hair and eye color, sex and limited life span? And how could we possibly have in our midst someone "born" to be an astronaut? That is, how can any human manage the physical, mental, and psychological demands of space flight? Far more mundane and commonplace human accomplishments are equally difficult to explain. How do we manage to drive our cars at freeway speed at night, seemingly guided by nothing more than our own headlights? How did we ever learn the nocturnal trick of inferring the true state of the road, its obstacles, and the other moving vehicles, from the tiny parabolas of light streaking across our retinas? How do we explain the melodic flights of a great jazz pianist or violinist, or the marksmanship of a golfer?
These questions are neither exotic nor frivolous. If behavioral potential has any significant degree of genetic underpinning, how do we even begin to tolerate the modern world we live in? Where is the fulfillment for a modern office- or factory-worker performing automated or repetitious tasks within a physical and social context that scarcely resembles any environmental ensemble from the formative eons of human prehistory? What are we to do if the human "gene pool" dictates the regeneration of stable percentages of individuals with aptitudes of little or no value to modern society? It is probably not a joke that computer games, spectator sports, television violence fantasies, and weekend hunting and fishing expeditions are the necessary transformations of outmoded but undiminished vestigial drives and skills that humans still carry with them. But is the creation of a menu of imaginative diversions our only recourse to the unremitting sway of an obsolete "hunter-gatherer" heritage?
In order to examine these questions, we will look at several examples of the cultural transformation of the human career. Here, using as guides people whose work is not only based in the hand but steeped in the oldest traditions of every human culture, we will see how powerfully a personal motive can invest and lend great meaning even to modern endeavors when they are oriented toward the satisfaction of basic human need. We will consider the celebration of food, the rituals of medicine and magic, and the affirmations of music. We will also consider what has been called "the permanent immaturity" of the human brain, and whether human culture may have become our own ("virtual") Galapagos, changing the direction and the timetable of human evolution.
Finally, and inevitably, we shall consider the impossible job we have given teachers, and the equally impossible job our children face, trying to absorb all that we insistently thrust upon them in the name of the future we would like them to have. If sports and video games rejuvenate the psychic connections to a primitive past, it is the schools that bear us into the future.
Since the Industrial Revolution, parents have expected that organized educational systems will tame and modernize their children and "prepare them for life." Such is the theory. But education--ritualized, formal education, at least--is not an all-purpose solution to the problem of inexperience and mental immaturity among the young. I was completely unprepared for the frequency with which I heard the people whom I interviewed either dismiss or actively denounce the time they had spent in school. Most of my interview subjects, although I never asked them directly, said quite forcefully that they had clarified their own thinking and their lives as a result of what they were doing with their hands. Not only were most of them essentially self-taught, but a few had engineered their personally unique repertoire of skills and expertise in open retreat from painful experiences in a school system that had dictated the form and content of their education in order to prepare them for a life modeled on conventional norms of success.
Apart from a grudging deference to what might be called the "right-brain lobby," what is there in our theories of education that respects the biologic principles governing cognitive processing in the brain and behavioral change in the individual? How does, or should, the education system accommodate the fact that the hand is not merely a metaphor or an icon for humanness, but often the real-life focal point--the lever or the launching pad--of a successful and genuinely fulfilling life?
We cannot escape the fleeting character of our lives: each of us moves within a single frame of a very long movie. But we are not passive recipients of the particular model of the brain that ended up inside bur own personal skull. We know beyond any doubt that education and experience alter the way the brain functions, but we cannot agree how best to apply that principle to the benefit of our children and ourselves. We devour the latest pronouncements of educational psychologists and cognitive neuroscientists, but do not know what the term "learning" means with respect to the brain itself, apart from the rather dry notion of altered probabilities of "synaptic strength" or "neural net" function. There is a lot we don't know.
When I begin work on this book, I believed both in the basic human desire for autonomy and in people's resourcefulness. Time and again the people I interviewed reaffirmed that belief, enlarged and enriched it. These people also made it clear that self-definition, even when it seems to have strong behavioral presets, is not a passive process. Both literally and figuratively, it must be a hands-on and hands-in affair. Sometimes it begins with the realization that the assumptions and demands of formal education must be ignored or actively resisted. Once launched, the process of self-education and development never really stops. People are born resourceful and they become skillful and "thoughtful" when they genuinely care about what they are doing. One begins to understand the origins--and learns to appreciate the interdependence--of human skill, intelligence, and vitality by looking at the details, one piece and one person at a time. That is the real story I hope readers will find in these pages.
Chapter One: Dawn
Our textbooks like to illustrate evolution with examples of optimal design nearly perfect mimicry of a dead lead by a butterfly or of a poisonous species by a palatable relative. But ideal design is a lousy argument for evolution, for it mimics the postulated action of an omnipotent creator. Odd arrangements and funny solutions are the proof of evolution paths that a sensible god would never tread but that a natural process, cpnstrained by history, follows perforce.
--Stephen Jay Gould
The earliest direct human ancestors were the australopithecines, "southern apes" of Africa who walked upright. The best known is Lucy, who lived some 3.2 million years ago in Hadar (in eastern Africa) and whose discovery created an enormous sensation not only in the anthropological world but with the public at large. Twenty years of careful research on her species have solidified her claim to primacy. She was the first anatomically bipedal human ancestor to be discovered, and she had an un-apelike hand and a chimpanzee-size brain. At the time of her discovery there had already been a few tentative suggestions that the modern human brain might have evolved as a consequence of the increase in tool use among Lucy's descendants. This specific assertion was made by anthropologist Sherwood Washburn, writing in Scientific American, just as the first reports of a tool-using hominid (Homo habilis) in East Africa were circulating.
Now it appears that man-apes--creatures able to run but not yet walk on two legs, and with brains no larger than those of apes now living--had already learned to make and use tools. It follows that the structure of modern man must be the result of the change in the terms of natural selection that came with the tool-using way of life.... From the short-term point of view, human structure makes human behavior possible. From the evolutionary point of view, behavior and structure form an interacting complex, with each change in one affecting the other. Man began when populations of apes, about a million years ago, started the bipedal, tool-using way of life.
Washburn's thesis actually contains three distinct assertions:
1. The brain and the musculoskeletal systems, as organs, evolve just as organisms themselves do, by modification of structure and function over time. Consequently, the behavior of any living members of any species, at any given time, reflects the operating characteristics of separate parts of the body in general, and (for Washburn), of the brain and musculoskeletal system in particular.
2. Two critical modifications in the musculoskeletal system contributed to the launching of the hominid line. The first--as Darwin himself asserted--was the adoption of a bipedal gait. Subsequent changes in the upper limb, altering the repertoire of hand movements in ways that favored tool use, were the final catalyst for the subsequent split of humans from the same primate line that had produced the great and the lesser apes much earlier.
3. The driving force behind hominid brain evolution (which Washburn, respecting Sir Arthur Keith's influential opinion, equated with increased brain volume) was not simply "selection pressure" created by external environmental change. The brain itself, and then society, ultimately overwhelmed the jungle (metaphorically speaking) as a destabilizing element and an organizing force in this process, with increasingly powerful effects on a host of adaptive anatomic and behavioral changes as hominid fines expanded their range into new habitats.
Washburn quite specifically insisted that the modern human brain came into being after the hominid, hand became "handier" with tools, maintaining that the brain was the last organ to evolve. It is a daring idea, one which requires us to look very closely at the evolutionary background of this hand, and at the changes that brought it its present anatomic configuration and functional capabilities.
That we know anything at all about the earliest human origins is due in large measure to the epic lives and work of Louis and Mary Leakey, whose critically important African discoveries beginning in the 1950s gave us not only our first vision of early hominid life but some very specific ideas about the antiquity of the human brain itself. Until recently, the search for a "founder" human brain has rested on the premise that distinctive human behavior, particularly language and tool use and the phenomenology of the mind, would be found to spring from brain size. Under that particular formulation, four reference dates assume special importance for anthropologists. The first marks the appearance of Lucy's clan, the australopithecines, beginning with Australopithecus anamemsis between 3.9 and 4.2 million years ago (mya). The second is the date of the first member of the Homo family, Homo habilis, who appeared about 2 mya. Next, sometime earlier than 1 mya, Homo erectus, also appeared. The fourth date is that of the appearance of modern Homo sapiens, established by fossils whose age has been dated at 100,000 years. During this time the brain grew from 400-500 cc (the australopithecines) to 600-700 cc (Homo habilis), then to 900-1,100 cc (Homo erectus), and finally to our own approximately 1,350 cc capacity. These dates give us a finite period to examine for evidence about the state of and ongoing changes in the hand that might be associated with both brain and behavioral evolution.
In point of fact, fossil specimens from arms and hands are even rarer than those of skulls. But the importance of finding and dating them can hardly be overstated: if we could learn something about the sequence and timing of modifications that prepared the primate upper extremity for refined tool use, we might be in a position to associate those changes with the emergence of the modern human brain. Enough is now known about the evolution of the primate upper limb at least to make clear what we need to look for next.
The earliest primates, so far as we know, were Paleocene mammals, mouse- to cat-size creatures who began to make the complex adaptations that an above-ground food source demanded by way of hunting and gathering skill. Taken as a whole, primates attacked the problem of successful tree life by accomplishing the following generic physical changes:
1. orbits and eyes moved to a forward position in the head, permitting binocular vision, certainly an advantage for navigating in three-dimensional space and for finding and catching small prey at close distances;
2. forearm and collarbone structure (a gift from insectivore ancestors) were modified to permit greater flexibility and perhaps greater safety in arboreal travel and dining;
3. paws retained the archaic but extremely useful five-ray (pentadactyl) pattern, permitting the animal to grasp with individual digits; toes and thumbs acquired the ability to close the gap between the thumb and first digit (i.e., they became convergent, though not yet opposable); nails replaced claws on the dorsal surface of terminal digits, while palmar surfaces acquired sensitive, ridged pulps--all these changes permitted improved climbing and locomotion along trunks and branches, and better grasping and holding of fruits, leaves, and insects;
4. the snout shortened, vision began to supersede smell as the dominant sense, and jaws, skull, and teeth changed, consistent with dietary change;
5. the brain changed in size and configuration, probably to accommodate the geometrically more complex (and physically riskier) living and hunting environment.
These changes were just beginning during the Paleocene epoch (65-58 mya) and had become well established by the end of the Eocene epoch (35 mya). It was also probably near the end of the Eocene epoch that the anthropoids (or "simians") appeared for the first time. The early anthropoids lived in the trees and were exclusively quadrupedal: none had yet made the shoulder or other upper-extremity modifications that permit suspended locomotion in trees. Those changes, and more advanced changes to the chest wall and the bony structure of the shoulder girdle permitting full brachiation, are believed to have taken place in the mid or late Oligocene.
By the beginning of the Miocene (24 mya), the anthropoids had branched into monkeys and apes. It is not clear why the monkeys and apes should have diverged, but the reason may be found in simple physics: apes are bigger than monkeys, and their size must have become a problem at the tops of the trees, where the supply of food is rich but the branches are small. Napier has suggested that a quadrupedal method of movement along the branches becomes unsatisfactory when body size and weight create an unfavorable center of gravity.
By the end of the Miocene epoch the African apes were moving out of the trees and back down onto the ground; the great apes were large animals, and their dietary habits had changed somewhat. Gorillas, the largest by far, had almost become a sort of land-based whale, large enough to be safe from attack by most predators, and able to exist on a very simple vegetarian diet. Chimpanzees were in a state of locomotor and dietary transition, with a highly mixed diet (including small animals) and very limited bipedal walking, usually assisted by weight-bearing on the knuckles.
At the beginning of the Pliocene (when the hominid story begins) the hand of monkeys and apes existed in several forms. First, in all these animals the four fingers had essentially the same form and functional capacity. The finger bones (phalanges) were relatively flat and slightly curved in the direction of flexion. In apes, and a few monkeys, there were strong attachments on the underside to keep the flexor tendons tightly held next to the bone. Opposition to the degree possible in the human hand was uncommon, although gorillas and some old-world monkeys could come close. Isolated digital movements were possible to permit scratching, picking, and digging movements, or for stripping, and small objects could be pinched between the thumb and the index finger. (Grooming is a favorite leisure activity with this hand among all its present owners, just as it is with us.) Objects could be held and carried in any of these hands exactly the way we hold a suitcase.
The greatest variability found in the prehominid hand was in the thumb, which tended to be short compared to the fingers: shortest in the chimpanzee and orangutan, more like hominids in the gorilla, sometimes even absent in monkeys. Interestingly, although the gorilla thumb most closely resembles the human thumb among these precursors, the gorilla has never been observed spontaneously to attempt tool use. Chimpanzees, with a much smaller thumb, stand out among pongids as prolific spontaneous tool users and as avid learners and improvisers in environments where the animals can be influenced by human artifact and teaching.
Another development that appeared with apes was a freeing of the attachment of the far end of the ulna (the major forearm bone of the elbow that meets the wrist on its small-finger side). This change must be considered critical to brachiation, since it increases the twisting range of the arm below the elbow needed to swing the body forward under the arm. It also allows the hand to tilt at the wrist away from the thumb.
We are now staring at a maddeningly blank page in our hand story, because the best example we have of a prehuman hominid hand is that of Lucy, who had acquired several humanlike features in the hand and also managed a major overhaul in pelvic and leg structure. In fact, it is her lower extremities that place her (and the other australopithecines) at, or very close to, the head of the line leading from the apes directly to man. The pelvis is short, and the configuration of the femoral joint at the hip and at the knee, like nothing ever seen before, is for all practical purposes the same structure humans now possess in an elongated version. A. anamemsis is thought to have walked upright on the basis of the structure of the tibia; in Lucy, the tibia, femur, and pelvis have been recovered, and there is no question that she was bipedal.
Mary Marzke, a physical anthropologist at Arizona State University, has spent a great deal of time looking at the hand and wrist bones of Australopitheens afarensis. Professor Marzke points out that although Lucy does have an opposable thumb, other primates also have this feature. Chimps and monkeys, in fact, are quite good at bringing the thumb to the side of the index finger. What they don't do well (as Lucy herself could not do) is bring the thumb tip all the way across the hand to the fourth and fifth fingers. Also, neither the apes nor Lucy flex the fingers on the ulnar side of the hand (the side with the little finger) toward the base of the thumb in the movement known as "ulnar opposition." We humans do this without the slightest sense of marvel whenever we grasp the handle of a hammer, a golf club, or a tennis racket and prepare to take a swing.
The advances in Lucy's hand are nearly impossible to appreciate without studying her wrist bones--fitting them together, moving them around, and comparing them to the wrist bones of other anthropoids. Having spent some years doing exactly this, Marzke concludes that Lucy's hand is at least partially "modern." The most impressive evidence for its modified design resides in the joint surfaces at the base of the thumb, index, and middle fingers, and in the changes in the size and orientation of the joint surfaces of the wrist bones closest to those digits. The thumb is long in comparison with the fingers, the ratio approaching that found in modern humans and in few other primates. Taken together, these changes move the radial (or thumb) side of Lucy's hand dramatically toward the twentieth century. The apparent functional advantages of the changes are:
* the thumb, index, and middle fingers can form a "three-jaw chuck," which means the hand can conform to, grasp, and firmly retain irregular solid shapes (such as stones);
* finer control can be exerted over objects held between the thumb and the tips of the index and middle fingers;
* rocks can be held within the hand to pound repeatedly on other hard objects (nuts, for example), or to dig for roots, because the new wrist structure is able to absorb (dissipate) the shock of repeated hard strikes more effectively than in the ape hand.
These changes would have given A. afarensis the capacity to conform the thumb and first two fingers to a very wide range of object sizes and shapes, allowing them to be held and manipulated easily on the thumb side of the hand. Changes in the ligaments suggest that Lucy had the capacity for prolonged periods of percussion using small stones.
The area in Ethiopia where Lucy and her close relatives were found is strewn with plain stones, so it is not fanciful to postulate that pounding and digging with stones (or wood, or parts of animal skeletons) was normal behavior for A. afarensis. But there is more. As we have noted, Lucy also had a pelvis and the legs of a primate capable of habitual bipedal locomotion. That means that she did not simply happen to get up on her feet occasionally; this was her natural standing posture. Yet her legs were not particularly long, and she probably didn't run any faster than her own ape neighbors or ancestors. What could possibly have been the survival value of this change in body structure? Marzke has examined the pelvic specimens carefully to determine sizes of muscles and their attachments and has come to a surprising conclusion: the bony and muscular structure (especially of gluteus maximus) strongly suggest that Lucy was equipped both to pound stones and to throw them, accurately and with speed. Lucy, in other words, might have been at home on a pitcher's mound.
Chimps can and do throw stones, but mainly to display alarm or aggression. They almost always throw underarm because they cannot use hip rotation to accelerate the torso during an arm swing. Lucy was not restricted in this way. She could have thrown overarm because her shoulder had the capacity for full brachiation (including forearm supination), her hand was capable of a "three-jaw chuck" grip, and her pelvis and its musculature permitted a whipsaw movement of the full axis of the body during the windup and throwing motion.
Throwing may well have become more an attack skill in Lucy than it ever could be in chimps, but a major improvement in clubbing had to await the changes in the configuration of the ulnar side of the wrist and hand, which came after the time of A. afarensis. The trick of ulnar opposition is unique to modern humans, and as the final piece in a mosaic of changes involving the entire extent of the upper extremity from shoulder to fingertips, it may well have unleashed the final stage of a unique mammalian strategy for long-term species survival. Opposition of the fourth and fifth fingers combined with ulnar deviation of the wrist permits a stick to be seated tightly in the hand and oriented along the axis of the arm, so that the swinging radius of arm-plus-stick (and, therefore, the force of a blow) increases. Having the ability to telescope the arm outward would convey a lethal advantage in close, hostile encounters, and once this obliquely oriented "squeeze" grip was introduced into the hominid hand, no adversary or prey in the same weight class was safe in its presence without being unusually fleet-footed, hard-headed, or thick-skinned."
A second effect of ulnar opposition can be seen in an improved precision grip, in which small objects are manipulated between the fingers without contacting the palm. The hand with this biomechanical ability would have been able not only to wield a large club and to manipulate and throw stones but also to use all five digits in the fine control of small objects. This one "small" modification, in other words, would have greatly enlarged the functional potential of the hand at both ends of the existing behavioral repertoire, opening the possibility for both a more combative and a more digitally dexterous individual.
Darwin is credited with the first formulation of the potential impact of an upright walking Posture: a hand freed of the obligation to support body weight can take on other tasks. But the paw-to-hand conversion began in tree-dwelling primates, and to evolve into what we now know as the human hand it had to be extensively reworked. The reworking involved far more than the paw itself-structural refinement was needed throughout the entire upper extremity, including the shoulder, before the hand could even begin to capitalize on the freedom it had been given. And during this long process, the owner of the hand had grown heavy, powerful, and aggressive.
In the earliest tree-dwelling primates, the need to cling to trunks and small branches favored a tactilely refined hand, and one whose movement and control repertoire had impressive range. from delicate, dissecting movements of individual digits to powerful grasping movements used both in sustained holding (prolonged suspension) and in the sequences of quick hold and quick release movements used in swinging and jumping. As experience with locomotion in the trees was gained, visual-motor and tactile-motor neurologic connections had to have undergone enormous change: the visual and kinesthetic support of successful arboreal acrobatics and predation demanded a bigger brain with very specialized control characteristics.
Brachiation itself may have begun simply as a biomechanical accommodation to increasing size and weight or to the advantages of suspended feeding (being able to reach for a meal not just from a sitting position but while hanging from a branch as well), or to both, as Napier proposed. But the resulting increased mobility in the upper arm effectively permitted the animal to locate either hand virtually anywhere within a sphere whose center was at the pivot point of the shoulder. The brain must have responded to this purely biomechanical change by increasing the complexity of its representation of the arm and hand in space, and there is no question that we have benefited from the overall change in very specific ways: without this freedom of movement, together with the neurologic ability to monitor and refine a host of new movements, ball and racquet sports would be nonexistent and car mechanics and plumbers would be useless working in cramped quarters with impaired visibility. In sum, we must infer that brachiation placed an enormous burden on the brain's kinesthetic monitoring and spatial computing power, since there were so many new places the hands could actually be while they were doing their job. Eventually there must also have been countless new tasks for the arms and hands that required differentiated use of the left and right hands, as well as the capacity for refined coordination of the two hands during bimanual tasks.
The importance of bipedalism itself must not be overlooked in assessing the impact of changes in the upper limb. The great apes and the larger monkeys have retained powerful musculature to support the head, which itself is a primary attack and defense structure for these animals. Cats, dogs, chimpanzees, and baboons are all equipped to use their jaws and teeth in mortal combat. But the survival of hominids, whose vertically oriented and delicately balanced head is a weapon only in verbal warfare, would either have depended on stealth as a defense or have come from transforming the upper extremity into a platform for offensive weaponry. As Marzke suggests, even Lucy would have been a remarkably dangerous predator had she been able to throw stones accurately. Once her descendants had the ability to prosthetically lengthen the arm, or to fashion more exotic projectiles and launching devices, size and build per se would have become essentially immaterial to the hominids, and the freedom to expand into new environments much greater.
Both the brain of the chimpanzee and that of the australopithecines weigh approximately 400 grams. No one knows whether brain enlargement is specifically related to increased tool use, but it is known that tools did not become complicated in their structure, nor were they kept and transported for long periods by their users, until quite recently. It is a virtual certainty that complex social structure--and language--developed gradually in association with the spread of more highly elaborated tool design, manufacture, and use; in the next chapter important new theories about the interaction of these major human advances will be reviewed.
We know that sometime after Lucy, a more mobile joint developed at the base of the small finger, but the origin of this modification in hand structure is unknown. To date, no fossil specimens from this region of the hand of H. erectus have been recovered, so it cannot be said whether the increase in brain weight from 400 grams to 1,100 grams occurred before or after this change in hand structure. This particular unanswered question is surely one of the great remaining buried treasures of human anthropology (see Fig. 1.7).
Given the also-ran status of the arm and hands of apes and monkeys, and the disappearance of the australopithecines, it is probably no exaggeration to say that the final biomechanical change at the base of the pinkie may have conferred an advantage to the hominid hand comparable to supplying its owner not just with gunpowder but with the biomechanical and computational infrastructure for an entire ballistics technology. Considering everything else that was already present, there was nothing this hand could not do if it could learn how to do it. And apparently with time, and with other opportunities and challenges encountered in new environments, the brain did rise to the challenge, and greatly modify itself in the process, since there is very little now that this hand, which makes tools that make machines that make computers that make machines and tools (and so on), cannot do.
The sequence from Australopithecus anamemsis through Lucy to Homo habilis, Homo erectus, and finally Homo sapiens has been well worked out and exhaustively documented. Woven into that sequence, certain behavioral traits acquired a dominant role in the struggle for species survival. In retrospect, we have come to view these as distinctively and exclusively human: tool use, language, reason, and self-consciousness. But we still search in vain for defining moments or events in this behavioral evolution; they were not so much implanted as emergent. Quadrupedal apes with occasional bipedality gave rise to habitually bipedal australopithecines; increasing use of the hand in the employment and modification of found objects conveyed a survival benefit to the next descendants. Early tool use and manufacture were associated with a modest increase in brain size in Homo habilis. The increasing refinement and perhaps specialization of manipulative, hunting, and offensive skills, as well as the ramification of social interactions enabled by more structured communication (and migration) by Homo erectus, had a further "kindling" effect on brain operations and structure. Finally, intraspecies cooperation and competition greatly increased the need for an elaborated social structure and communication and for coordinated industry, all of which demanded a more powerful and more versatile brain. When he finally had enough brain to be able to guess what the brain itself was doing, Home pronounced himself sapiens.
Unless we are prepared to argue that language and reason appeared de now in the cortex of the brain, we must grant Professor Washburn his point: the whole fist of recently acquired and uniquely human behavioral attributes must have arisen during the long process of brain enlargement that began with the expansion of novel and inventive tool use by Homo habilis and with the myriad new experiences and environments that successful employment of such behavior inevitably provided.
Recently, anthropologist Peter C. Reynolds has pointed out that although stone tool manufacture is usually regarded in his profession as a solitary endeavor, it need not have been. Reynolds suggests that complex tools, such as axes and knives, may in fact have been customarily manufactured by small groups of people working together, each performing some part of the task. The possible importance of this alternative transcends the mere pragmatics of shared labor. Any such cooperative efforts would have required a means of communicating, which would probably have taken the form of hand signals and other bodily gestures or vocalizations, or both. In other words, cooperative tool manufacture could have provided a crucial precondition for the evolution of language. An emerging language based in the growth of cooperative tool manufacture would have fostered the evolution not only of a more sophisticated tool manufacture but also of a more complex social culture and a more refined language. As has already been pointed out, these two behaviors, mutually interdependent and mutually reinforcing, would also have been capable of gaining enhanced representation in the brain. To whatever extent language and tool use became specific, heritable traits (even when they demanded priming through cultural exposure), they would have profoundly altered survival prospects for all individuals with this genetic endowment.
A related and more practical question for us concerns the neurologic and behavioral implications of an obligatory hand-brain marriage on a collapsed time scale. What might be the connection between tool use, language, and thinking during the span of a single human life? Recall that Washburn said (referring to what is fixed in our own genetically determined anatomy), "From the short-term point of view, human structure makes human behavior possible."
If language and the employment of the hands for tool manufacture and tool use co-evolved--effectively forging a new domain of hominid brain operations and mental potentials that we collectively refer to as "human cognition!"--then we should find analogous links, or reinforcing effects, between purposive hand use, language, and cognition in the individual histories of living people. Think what this means. "Intelligent" hand use might not be merely an incidental bequest of our hominid heritage, but--along with the language instinct--an elemental force in the genesis of what we refer to as the "mind," activated at the time of birth.
© Copyright 1998 Frank R. Wilson
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