Thumbs, Toes, and Tears

by Chip Walter

  This dearth of toolmaking ancestors is one reason why the world was stunned in 1964 when primatologist John Napier, paleoanthropologist Philip Tobias, and the dean of human evolutionary theory, Louis Leakey, wrote in Nature that they had found among the dust and rock of Olduvai Gorge in Tanganyika (now Tanzania) evidence of the first toolmaking creatures ever. This protohuman, Leakey, Napier, and Tobias told the world, was not an australopithecine. It had a larger brain than any ancestor found this far back in the fossil record. And it had a very humanlike hand. “The hand bones resemble those of Homo sapiens sapiens [modern humans],” they wrote, “in the presence of broad, stout, terminal phalanges on fingers and thumb…”

  The scientific world dropped its collective jaw. A two-million-year-old hand that looked human was big news. But even bigger, perhaps, was the discovery of simple tools found in the same area and strata of rock as the creature’s bones—flakes of sharp stone used for cutting and scraping.

  Frankly, this surprised Leakey and his colleagues because the pieces of skull and jaw they had found indicated that the brain of Homo habilis was not quite as large as they would have expected in a true toolmaker—only about 680 cc (roughly half the size of the average human brain). Despite this, the scientists felt that the creature should be classified in the genus Homo, indisputably making it our direct ancestor. After all, if these creatures could make tools, they reasoned, whatever brains they had must have been enough to qualify them as one of us.

  In the more than forty years that have passed since Leakey’s discovery, anthropologists have debated exactly where Homo habilis fits into the family tree. Only four habilis discoveries have been made, so their pedigree has been difficult to resolve. But one issue that seems beyond debate is that Homo habilis had something that Lucy and other australopithecines before it didn’t—elongated, fully opposable thumbs that are essentially identical to ours. As Napier put it, “The hand without a thumb is at worst nothing more than an animated fish-slice and at best a pair of forceps whose points don’t meet properly. Without the thumb, the hand is put back 60 million years in evolutionary terms to a stage when the thumb had no independent movement and was just another digit. One cannot emphasize enough the importance of finger-thumb opposition for human emergence from a relatively undistinguished primate background.”4

  Habilis’s thumb had evolved to the point where it made toolmaking possible. Because of its distinctly human shape and mechanics, Homo habilis could do something never before seen in the natural world: cup its strong palm and fingers around an odd and irregularly shaped chunk of flint rock, grab another smaller stone the way you might grasp a baseball (two fingers on top and the thumb below in a grip known as the “three-jawed chuck”), and repeatedly but precisely whack the larger stone.

  Easy as this seems, no other primate can do it. Mary Marzke, who has made a career of understanding how our hands evolved and work, has noted that all of this was made possible “by a unique pattern of hand proportions and joint-and-muscle configurations that permit cupping of the hand and the formation of a wide variety of grips.”5

  In Homo habilis, evolution had shaped a hand that was the anatomical equivalent of a jack-of-all-trades. It could hold, twist, turn, push, and pull unlike anything that had come down the evolutionary pike. And this in turn made it capable of shaping itself in an unusually large number of grips and positions.

  This was, to say the least, a good thing for H. habilis because he needed all the help he could get. By the time his kind had emerged, Africa’s savannas were growing even less forested than they had been previously thanks to a new climatic heat wave. The clustered trees that remained, and the nuts and fruits they provided, were shrinking still further. But larger mammals, so-called megafauna, were continuing to evolve on the expanding grasslands, and they often fell prey to the savanna’s big cats, leaving their carcasses available to those animals that couldn’t make the big kill themselves but didn’t mind partaking of the leftovers. If H. habilis could become a resourceful scavenger, he might do pretty well.

  The “three-jawed chuck” is a grip unique to the human hand. It enables us to use the thumb, index, and middle fingers to grasp irregularly shaped objects, such as a stone, and use it as a tool, or transform a stick into a lethal club by cupping it in a position that extends the power of our arm, and, with it, the force of the blow it delivers. (Reprinted from “Evolutionary Development of the Human Thumb” by Mary Marzke. Used by permission of Mary Marzke.)

  Strong and nimble thumbs helped him accomplish that. With them, and the hands they made possible, he transformed chunks of stone into honed knives with exceptionally sharp edges and then put them to work butchering animals the size of hippopotamuses and elephants. These weren’t a hunter’s weapons; they were artificial versions of a jackal’s jaws or a vulture’s beak. Carrion tools. But they represented vitally important advances. At least that is what fossil finds in Olduvai Gorge have indicated.

  To test just how well knives of this kind might actually have worked, Nicholas Toth and his archaeologist colleagues from Indiana University visited the same locations where H. habilis lived two thousand millennia ago. Once there they took into their hands the same flint rock out of which H. habilis had fashioned tools and created their own knives by carefully hammering a small chunk of rock against a larger “core” stone. With every blow of the “hammer,” a razor-sharp shard of the core would fall to the ground.

  East Africa, they found, was loaded with the raw materials used to fashion the first artificial tools. The stone knives were not difficult to create, if you had the thumbs for it, and they managed to produce exact replicas of the ancient tools again and again. Then came the hard part.

  They took the sharp-edged stones into the savanna, where on two different occasions they located the carcasses of elephants that had recently died of natural causes. And then, like members of a small troop of Homo habilis, they set to work flaying and carving the animals up. Toth and Kathy D. Schick described the experience in their book Making Silent Stones Speak: Human Evolution and the Dawn of Technology:

  “Somewhat daunted, we approached our task equipped with simple lava and flint flakes and cores, which looked more and more paltry as we got closer to the impressive body. Initially, the sight of a twelve-thousand-pound animal carcass the size of a Winnebago can be quite intimidating—where do you start? We had never seen a field manual on pachyderm butchery, and they aren’t like smaller animals: you cannot move the body around (for instance, flip it over to get a better vantage) without heavy power machinery. You have to play the carcass where it lies…

  “Despite the success of our tools in dozens of other butcheries, we were not really sure they were up to this task. We were amazed, however, as a small lava flake sliced through the steel gray skin, about one inch thick, exposing enormous quantities of rich, red elephant meat inside. After breaching this critical barrier, removing flesh proved to be reasonably simple, although the enormous bones and muscles of these animals have very tough, thick tendons and ligaments, another challenge met successfully by our stone tools.”6

  …

  These tools and abilities bestowed H. habilis with an evolutionary edge no other animal had ever enjoyed. At the very time H. habilis was carving carrion, other bipedal primates, such as Paranthropus boisei, were living nearby taking another approach. P. boisei ate tubers, grubs, berries, and nuts, not meat. But with his stone knife, H. habilis, who already had a larger brain, was now able to dine on deinotherium or hippopotamus carcass, which in turn provided increased health and the raw protein needed for growing still larger brains.

  Not that he was a master hunter. At four feet and a hundred pounds, he was far from fearsome, but thanks to his tools he could piggyback on the strength, speed, and ferocity of other animals and supply himself with food that eluded his cousin primates. In time H. habilis’s handmade tools put more evolutionary distance between himself and the australopithecines roaming the savanna. He was a technological ani
mal with all of the advantages technology affords. While the fossil record indicates that Paranthropus boisei and its relatives actually escaped extinction longer than Homo habilis, eventually their line led nowhere. H. habilis, however, evolved into other, increasingly intelligent species of toolmakers, such as Homo erectus and Homo ergaster, lines that eventually led directly to us.

  An adult Paranthropus boisei skull. (Used by permission of the Smithsonian Institution.)

  …

  While H. habilis’s tools enhanced his survival and accelerated brain growth, they set even more far-reaching events in motion. The thumbs that made tools possible were also shaping a new kind of mind. Leakey and Napier eventually argued that it wasn’t the tools alone that H. habilis fashioned that separated him from the rest of the primate pack, it was his mind. Or more accurately, it was a brain capable of conceiving and making tools that truly distinguished him.

  It was Raymond Dart who suggested to Leakey and his colleagues that they name the new, toolmaking creature they had discovered Homo habilis. Most times this is translated as “handy man,” but as the team pointed out in their paper, habilis also means “able, mentally skillful.” That insight may have turned out to have been more accurate than even Leakey and his codiscoverers suspected, because as scientists have realized since, mental skill and manual dexterity go very literally hand-in-hand.7 Or put another way, the physical world in which our ancestors evolved shaped the mental world in which we live today. The two of them cannot be separated.

  …

  More than twenty-three hundred years ago, the great orators of ancient Greece (and later Rome) employed a terrifically creative technique for remembering long speeches and poems. They called it lopoi, the Greek word for places. (The equivalent Latin word, which we still use today, is loci.) Mnemonic devices were a necessity in those days. Paper and pen were still rare, and it wasn’t a simple matter to jot thoughts and passages down like we do. Orators like Demosthenes and Cicero would sometimes speak for hours, enthralling their audiences and devastating their opponents in debate while they used nothing more than loci to track the threads of their logic.

  They did this by imagining a physical space they were familiar with. Think of walking up to your home. There is your front porch, your door, the hallway and living room. Imagine you want to remember a grocery list. You simply picture yourself walking up to your house and associating the things you want to buy with each location: milk on the porch, apples at the door, bread on the floor of the entry. Once you have linked an item with a specific location in your mind, all you have to do is walk again through your imaginary house, and each reminder is there waiting in the right order. With a speech it’s a little more complicated than this (the “items” are more abstract), but the idea is the same: associate what you want to remember with moving through familiar physical spaces.

  There is no obvious reason why this visualization technique should work any better than simply memorizing a list of concepts (or groceries) you want to recall, but it does. And it does because brains evolved to map the physical world long before they evolved to handle abstract thought. We live in three-dimensional physical space. We move forward and backward, left and right, up and down. On the most basic level our gray matter relates to the world in these very physical terms. Even the simplest bacteria and the smallest fish “understand” the world this way. If they didn’t, they would be motionless and paralyzed—incapable of escaping a predator and powerless to pursue food when they sensed it. Being alive requires understanding space and moving through it.

  We tend to assume that the thinking that buttresses high-minded and complex abilities such as language, philosophy, strategy, reflection, invention, and creativity are not truly connected with the physical world. But there is mounting (some argue irrefutable) evidence that because our brains evolved to move us through physical space, that evolution has deeply shaped the way we think about everything. Linguist George Lakoff and philosopher Mark Johnson have pointed out that as loaded as our mental lives are with intangible concepts such as importance, similarity, difficulty, desire, intimacy, and ambition, we actually think about them in very concrete terms. We “see” what someone means. We “grasp” an insight. If a concept eludes us, it goes “over” our heads. We “crush” opponents; “fall” in love; “kick” ideas around; feel “squeezed” when we are under pressure; and “hold” someone in high esteem. We even express emotions in terms of distance or height. We are “close” to our friends, “distant” when angry. We feel “down” or “up.” If something is important, it is “big.” If a movie or a book is bad, it “stinks.” Even something as abstract as time is conceived and expressed in physical terms. The past is “behind” us and the future lies “ahead.”

  Metaphors like these are pervasive in every language and throughout human thought, whether you hail from Mongolia or Tierra del Fuego.8 And they are wired into the human brain as early as infancy and toddlerhood. Johnson calls this process “conflation.” Babies, he says, are not mentally capable of fully separating the experience of one thing that is often associated with something else in their lives. For example, the affection an infant experiences is usually associated with the warmth and security of being physically held, so she “conflates” the two experiences—being close to someone physically equates to the security that closeness creates. Later in life, of course, we learn that affection and physical warmth are not the same thing, but because they were in our infant experience, we continue to link them conceptually.

  Other experiments indicate that when we think of the word “fall,” for example, we may experience feelings of fear and failure that we associate with falling because neural connections in our brain have physically connected them at the synaptic level.9 This means our talk of “warm smiles” and “close friends” may be neurologically, as well as conceptually, harnessed together.

  This very likely explains why we find it easier to remember ideas when we associate them with a physical activity, such as walking through our house. But with the arrival of hands, especially thumb-opposed hands, our brains developed an even more physically precise perception of the world because now rather than passively reacting to our environment, thumbs made it possible to intentionally grasp and manipulate it in ways nature had never seen before. That would link two shattering events in human evolution that most of us might not assume are connected: toolmaking and language.

  …

  Patricia Greenfield, a developmental psychologist at UCLA, has found that there are remarkable connections between the way children use their hands to control objects, and the ways in which we all organize symbols in our minds before expressing them in words.

  In one test Greenfield asked children of three different ages—six, seven, and eleven years old—to solve a puzzle.10 Twenty sticks were laid on a table and positioned so they formed a series of connected boxes. Each child was then given an identical set of sticks and asked to re-create the same pattern of boxes. The way each group approached the problem provided some surprising clues into the way our brains organize thought.

  The six-year-olds all had a characteristic way they went about tackling the problem. They laid down a stick, and then used the next stick to connect to the last one. They never created a separate box that wasn’t linked to the sticks they had already laid down. In fact, they always linked the stick in hand with the last one they put on the table. Basically, they were feeling their way through the problem until they painstakingly reconfigured their sticks to look like the pattern that had already been laid out before them. They really were incapable of doing it any other way.

  Seven-year-olds dealt with the challenge a little differently. They didn’t always link the last stick to the previous one. They sometimes created a separate, disconnected box here and then another there. Then they linked separated boxes with other sticks until the problem was solved. These children weren’t feeling their way through the puzzle. They were far more creative and confident than children only a
year younger, according to Greenfield. Rather than slavishly imitating the pattern stick by stick, they were now generalizing the whole pattern, which they then went on to build in separate chunks that they eventually connected.

  Eleven-year-olds made a quantum leap. In fact, when they were presented with this puzzle they treated it something like the way a virtuoso pianist might treat playing “Twinkle, Twinkle, Little Star.” They seemed to stow the whole pattern in their minds at a glance, where they mentally held it while they considered other aspects of the problem. (This is a unique human ability called “working memory,” which allows us to put mental constructs aside while we tackle something else without losing track of the original concept). In any case, the eleven-year-olds didn’t see the puzzle as a stick-by-stick problem, or even a box-by-box problem. They played with the whole pattern, re-creating it in all kinds of ways, playfully; a stick here, a stick there, boxes connected by boxes, whatever they could imagine. For them it was all simple.

  Greenfield believes that children at these ages approached her problem so differently because specific parts of the brain involved in organizing objects have to physically link before they can solve the puzzle in increasingly sophisticated ways. She also believes that the ways in which children physically re-create the puzzle—the way they choose to connect the sticks—parallel the ways in which they organize their thinking and their language.

  Consider, for example, the approach we take at an early age to stringing together words. Very early on we manage it well enough with basic information, like “Me want bottle.” But later, ideas become more complex and words are arranged in more complicated ways to communicate more intricate concepts. “May I please have the bottle?” (Well, usually it’s “Can I please have the bottle?”) Or, “May I have the bottle of milk over there on the kitchen counter?” The point is that we figure out where to place words and ideas in the patterns of our sentences and thought not unlike the ways in which we figure out how to place objects in a puzzle. Words serve the same function in language as objects do in Greenfield’s stick-box experiment. If you can put the sticks (words) together in the right configuration (syntax), you solve the puzzle and construct something that makes sense. The language equivalent of this is first the conception or acquisition of an idea, and then a sentence that expresses it. In this way, words and concepts are like virtual, imaginary objects we move around in our minds, not unlike objects we move in the physical world.