by Mark Pagel
The last unoccupied region of the world was now the Pacific Ocean. Even though it lapped up against the shores of South America, that continent’s new occupants evidently were not sailors. Instead, the occupation of the Pacific would come out of the geographical Far East (or from the vantage point of the people in South America, the West). But it would have to wait until around 6,000 years ago when other descendants of Siberian populations moved out from present-day China and Taiwan. They migrated southward through the Philippines and then sailed eastward out into the vast Pacific, carried by newly developed and increasingly sophisticated boat technologies. One by one, thousands of far-flung islands would be occupied as these Lapita people, so named by archaeologists for their distinctive pottery designs, learned to navigate by the stars using “star maps” made from knotted string. They would do this thousands of years before the Vikings made their tentative journey a few hundred miles across the North Atlantic to what is modern-day Britain.
The settlement of the Pacific was a breathtaking and daring accomplishment that can really only be appreciated by going to one of these remote Pacific islands to get a sense of the scale and danger of that ocean. Most of the islands would have been small and well out of sight distance from one another, and no one had the slightest idea what if anything was out there. Still, something pushed these Austronesian people on, and their boats eventually reached the far-flung shores of Easter Island, and the somewhat later they finally made contact with South America, probably somewhere in present-day Chile. There they might have had a surprise because unlike the thousands of islands they had occupied throughout Oceania, this piece of land had people on it. They might also have felt a strange sense of déjà vu because these were people from whom they had separated maybe 20,000 or more years earlier, perhaps somewhere in the Altai Mountains of present-day southwestern Mongolia, and whose broad facial features they might have shared. Polynesian people went on to discover New Zealand in the south and Hawaii in the north only around 1,000 years ago. Reaching those islands, given their remoteness and the technology that was available, must surely rank alongside going to the Moon, and even then we knew the Moon was there before we set off.
The modern-human occupation of the world was now complete, all within a few tens of thousands of years after leaving Africa; and most of this within the first 20,000. It was an occupation that had begun back in Africa when as few as several hundred to several thousand people left that ancestral continent, so that today, remarkably, and in such a short period of time, all of us on Earth trace our ancestry back to this small and intrepid band. By the end of the Polynesian expansion, humans now inhabited deserts, savannah, prairies, marshes, rain forests, and ice. They lived on tops of hills, in valleys, islands, and most places in between. They spoke thousands of distinct and mutually incomprehensible languages. They had evolved a variety of different mating practices such that sometimes men had more than one wife, other times women had more than one husband, and in other societies people practiced monogamy. In some societies men would have to pay fathers bride prices for their daughters in marriage, in other societies fathers had to pay a dowry to get their daughter married. Some societies transmitted their wealth—in the form of belongings and territories—down paternal lines, while others transmitted it down the maternal side of the family. They constructed all manner of different kinds of shelter, ate everything from seeds to whales, and engaged in bizarre belief systems and behavioral practices. A single species had acquired a global reach, and specializations, lifestyles, and beliefs as varied as collections of different species.
Archaeological and fossil remains show that as humans occupied the final uninhabited regions of the world, they came with the same voracious momentum that had enabled them to displace, outcompete, or simply kill off premodern human populations. In North America large mammals such as the saber-toothed tiger disappeared soon after our arrival, and in New Zealand and Polynesia the huge flightless Moa birds and giant turtles survived only a few centuries in our presence. Having never before encountered our kind, they were not prepared for the highly efficient and hungry conquering machines that they met. It is a pattern that continues today. Wherever humans are found in large numbers the ecological world around them has been stripped of its diversity, with most of the animals and many plants having been driven out or made extinct. Vast swathes of Northern Europe are devoid of nearly all the mammal species that would have been present when modern humans first appeared. It is a trend we have continued right up into the present day. The title of Rachel Carson’s famous paean to ecology, Silent Spring, is a lament to the near eradication of songbirds in America.
IMITATION, SOCIAL LEARNING, AND CULTURE
THE RISE of the genus Homo is principally the story of a single species—our own, Homo sapiens sapiens, as it is sometimes called to distinguish it from the Neanderthals, or Homo sapiens neanderthal-ensis. Where all the other Homo species in our history, including the Neanderthals, were confined to the environments their genes adapted them to, modern humans were able to spread around the world by producing technologies that allowed them to transform the world to suit their needs. The puzzle and irony of this difference is in the names. Homo sapiens means “wise man,” but as we have seen, the genetic differences between ourselves and the Neanderthals are slight, amounting to less than one half of 1 percent in the sequences of our genes, and yet only one of these wise men occupied the world.
What made it possible for our species, the “wise wise man,” to survive in and exploit nearly all of the world’s habitats, where so many others, including the other wise man, had failed or in most cases never even ventured? The flowering of culture, communication, and symbolic thinking that distinguishes our species from all others can probably trace its origins to a development that was almost certainly minuscule on a genetic scale, but vast in its potential. Modern humans seem, uniquely among animals, capable of something that psychologists and anthropologists call cultural or social learning. Social learning can be fiendishly difficult to define but has—when applied to humans—two important features that together make the entirety of our cultural achievements possible and effectively open up an unbridgeable gulf between ourselves and all other animals. One is that we are capable of sophisticated copying and imitation of new or novel behaviors merely by watching or observing others, and without the need for specific training or rewards. We can then transmit these new behaviors faithfully to others. The second feature is that humans act as if they know what they are copying and why, and so they can choose to copy the best from among a number of alternatives, and even attempt to improve on it.
Of course, all animals can learn, and there are numerous examples of animals behaving in ways that give the appearance of social learning, at least for some for highly specific tasks. For instance, in the early 1920s, residents of the village of Swaythling in the south of England began to notice holes poked into the foil tops of the milk bottles that had been left on their doorsteps by the milkman. They soon came to realize that a local bird, the blue tit, closely related to the American chickadee, had learned to peck at the bottles to obtain cream off the top. These birds even recognized that the different colored foil tops on the milk bottles identified some as having more cream than others. This behavior spread throughout southern England for the next twenty years, and is often quoted as an example of one bird learning from another by social learning. Other examples are the washing of food at the seaside by Japanese macaques, and the well known “fishing” by chimpanzees in which they use slender sticks to draw ants or termites out of their underground nests.
These behaviors are compelling to watch, but on close inspection it is apparent that the animals are not so much copying each other in any exact way, as having their attention drawn in some very general way to something they can do. Equally, none of these behaviors seems to improve over time—the birds don’t get better at obtaining cream from milk, and the macaques don’t get better at washing food. By comparison, if you wer
e a hunter-gatherer living in our distant past and you witnessed for the first time two people making hand axes by chipping or “flaking” them out of larger pieces of stone, you would probably understand or be able to work out what they were for, and you might even recognize differences between them that meant one of these hand axes was going to work better than the other. Later, you might try to imitate the chipping actions of the person who made the better one, and you might wonder how to improve on it. Maybe you want to make it sharper or perhaps less prone to breakage. Even if initially the two axes seemed the same to you, you might later notice that one of them seemed to be sharper or easier to hold, or you might notice that one of the two people was able to skin that large animal they had just killed better than the other. In either case, it would be obvious which one to copy.
Obvious to you at least because, incredibly, we seem to be the only species that can do this. We can learn new behaviors according to the old saying, “Monkey see, monkey do,” but the surprise is that monkeys, and other animals, for the most part, cannot, or when they can, it is often limited to highly specific behaviors that already exist in their repertoire of behaviors anyway. Thus, if you were like other animals watching the two people make a hand ax, you might not pay any attention at all, and if you did, you might make nothing of it. Instead, their actions might do little more than draw your attention to stones, and you might even pick two of them up and bang them together, because this is something you do anyway. One of the stones might even crack and chip off a piece that you might then pick up and later discover, again by chance, that it was useful for chopping. Biologists and anthropologists who study animal learning call this stimulus enhancement, and it is distinct from true social learning. The distinction is subtle but important because, unlike true social learning, learning from stimulus enhancement doesn’t seem to translate into new or purposeful behaviors that faithfully copy or pick up where others have left off. Rather, it just makes use of old or even hard-wired behaviors already in an animal’s repertoire, even if sometimes in a slightly new context. Pecking is something that birds do anyway—it is for many birds the principal way they obtain food. Pecking at the tops of milk bottles, then, might be less a case of precise social learning than of stimulus enhancement.
Battles rage among scientists who study animal behavior over whether some specific action is a case of social learning or stimulus enhancement. But if we apply a simple test most examples provide a clear answer: does a species show any evidence of the behavior becoming more sophisticated and refined over long periods of time? This test is crucial. If an animal lacks true social learning, each new generation will have to rely on trial and error, catalyzed only by a little push of stimulus enhancement, to discover for themselves how to perform some action or use some tool; they do not seem to learn directly from others. For example, chimpanzees are often lauded as the champions of culture in the rest of the animal world. Anthropologists have documented that chimpanzee groups living in different parts of the forest have about thirty different cultural traditions in such things as how they fish for ants and termites, or how they use stones to crack open nuts. But these differences among chimpanzee societies almost certainly owe more to the vagaries of local circumstance than to any real design on the part of the animals, because there is no evidence that the chimpanzees, or for that matter any other animal, get better at using or producing these tools—they don’t build better nut-cracking devices or invent better ways to fish for termites. Instead, being surrounded by other chimpanzees that use the sticks this way seems to make it more likely that a naive one will pick up a stick and poke and prod things with it—things chimpanzees do anyway. Then, just by chance this might lead to acquiring a few ants or termites to eat and this reward seems sufficient to keep the behavior going.
What this means for most species is that any new innovations or improvements seem limited almost entirely to what an individual can produce on its own, because, they don’t seem to recognize and then acquire them from others the way we do: they don’t seem to be aware of the innovations, much less whether they are useful or not. Even if there were a chimpanzee-Einstein, its ideas would almost certainly die with it, because others would be no more likely to copy it than a chimpanzee-dunce. And this means that, lacking social learning, there is no real cultural ratchet that leads to improvement over time, no shared reservoir of accumulated ideas, skills, and technologies. Instead, each individual chimpanzee is left to come up with its own rules and own particular styles of nut cracking, or termite fishing. Indeed, were we to go away for a million years, upon our return the chimpanzees would probably still be using the same sorts of tools to fish termites from the ground. The same is true of the birds pecking at milk bottles or the macaques washing their food. This simple difference creates a vast difference between the other animals and us. Just imagine if each generation we had to learn for ourselves how to make fire, flake hand axes, make bows and arrows, sew clothes, navigate by the stars, or build shelters or hunt game, not to mention how to build printing presses, computers, and spacecraft.
The reason animals don’t seem to move beyond stimulus enhancement or having their attention drawn to things is that they don’t seem to put themselves inside the minds of others, or, as Michael Tomasello argues in his Cultural Origins of Human Cognition, they seem to lack a “theory of mind,” or the ability to adopt another’s point of view. They don’t seem to assume as we do that someone is doing something for some reason or purpose. Lacking a theory of mind is why a chimpanzee can be taught to paint, but the animal is not really “painting,” just spreading paint onto a surface, and chimpanzees will go on doing this, aimlessly painting over what they have done until they grow tired of the activity or until someone takes the brush away. They don’t seem to “get” the bigger idea of what they are doing or why. Indeed, a chimpanzee can be taught to use a saw to cut wood, push a broom to sweep a floor, drink tea from teacups, exchange plastic tokens for food, and even wash dishes, given a sufficient reward. But before you think of employing one around your house, be aware that it will as happily wash a clean dish as a dirty one. This is because it is not washing dishes to clean them, as we do, but to get a banana.
Even in humans, a theory of mind emerges only sometime around a child’s third or fourth year. A procedure known as the Sally-Anne test shows a child two dolls: Sally and Anne. Sally has a marble that she (with the help of a human experimenter) puts in her basket. Then Sally leaves the scene. While Sally is away, Anne takes the marble from Sally’s basket and puts it in her box, which differs in appearance from Sally’s basket. Sally then returns and the child is asked where Sally will look for the marble. Children younger than three to four say she will look in Anne’s box (intriguingly, many people who suffer from autism also respond this way). But older children realize that Sally can have beliefs that differ from theirs, and they correctly say she will look in her basket.
There are many varieties of these “false-belief” tests, and they can be difficult to interpret, but they all point to three to four years of age as being a critical period during which children’s awareness of others’ minds develops. To be fair to the other animals it must be allowed that some of them, especially some birds, behave as if they have an awareness of what others are thinking. For instance, if the small bird known as the nutcracker (and some other jay and crow species) sees another bird watching it while it hides its food, it will return alone later to hide the food in a new spot. What matters for this discussion, though, is that no other animal ever seems to get as far in their understanding of others’ minds as a four- to five-year-old human. Even among the Great Apes, any theory of mind seems to be no more advanced than that of a human two-year-old.
It is staggering and baffling to us that other animals could be so dim-witted. It is not that they are stupid: a chimpanzee is better at being a chimpanzee than you are. It is just that they lack social learning, and this small difference has made all the difference. But what of our more recen
t ancestors, such as the many now-extinct species in the Homo lineage? The African Rift Valley is an angry tear in the Earth’s crust that stretches for thousands of miles. It was in a part of the Rift Valley in Tanzania called the Olduvai Gorge that the pioneering archaeologist Louis Leakey discovered objects over 1 million years old that appeared to have been deliberately and intentionally shaped by hands. Later work established that these were Homo erectus hand axes, and they were often found near to bones with cut marks on them made by the same hand axes. For many archaeologists this time in our history, perhaps 2 million years ago, is one of those defining moments, a time we can look back on romantically as being the moment that creative thinking arose. These early humans, it seems, had acquired not only a compulsion to make things but also the insight that they could alter and improve them. It is that “light bulb” moment in Stanley Kubrick’s 2001: A Space Odyssey when the ape throws a bone up into the air. We watch it tumbling end over end, and as it falls back to the ground the bone transforms into a spaceship on an interstellar mission.
But the archaeological record tells a more prosaic story about our ancestors’ creativity. Remarkably, from careful sifting through layers of strata, archaeologists have been able to determine that our H. erectus ancestors living on the African savannah stubbornly chipped the same hand axes out of larger stones for nearly all of their 1.8 million-year history, without making any serious alterations to its form or function. For tens of thousands of generations of parents and their offspring, and the individuals watching them, this species produced the same basic tool. Their culture—their toolkit—wasn’t evolving, and this is not what we expect of an animal with social learning. It is not even clear that the Neanderthals possessed the capabilities for social learning, or if they did, they were not nearly as sophisticated as ours. The Neanderthals would have been recognizably similar to us, yet hauntingly different, being stocky and muscular, with large bulbous noses. But despite having brains at least as big as ours, the Neanderthals lacked most of the outward signs of sophisticated culture so common to modern human archaeological sites of the same period. The Neanderthals did not produce any art, they didn’t have musical instruments, and there is no evidence that they carved figures.
