The Accidental Species: Misunderstandings of Human Evolution

by Henry Gee

  The essentially unchanging nature of hand axes suggests that the techniques used to make them were not entirely learned or taught, but were to some extent hardwired. Even if Homo erectus adults taught them to their offspring, there was absolutely no conception that hand axes could be made in anything other than the prescribed way. And if, in the sequence of steps used to make a hand ax, a blow went awry, spoiling the blank, the maker wouldn’t shrug his shoulders and make the best of a bad job, converting what might have been a hand ax into a scraper, a Large Hadron Collider, or a hi-fi cabinet. No, he would start all over again with a new blank. There are some Paleolithic sites at which hand axes have been recovered in great abundance, in various stages of manufacture. These sites are exceptional—but the exceptions still require some kind of explanation.

  Perhaps most tellingly, there is much argument about what hand axes were for.17 Although they are very beautiful,18 they are in many ways impractical. A knife or chopper made of stone is easier to hold in the hand if some part of it retains the original, smooth stone surface—but hand axes are flaked all the way round. The raw edges of a cut flint are extremely sharp to begin with, but the edge soon dulls. So if you are going to make a chopper to smash bones or a knife to slice through flesh, it’s quicker and easier just to strike a flake and get on with it, rather than commit to the immense artistry required to make a hand ax. So what else might hand axes be for? Currency? Symbols of status? Sexual display?19 It’s impossible to know. What we can say from the evidence is that hand axes represent the kind of stereotypical behavior associated with other examples of animal technology, such as the nests made by birds, woven with great skill but always in the same general way. Whereas it is true that some aspects of behavior that seem stereotypical are to an extent learned—birdsong is a good example—the songs of birds are always pretty much the same and characteristic of each species. The might have been true for hand axes and Homo erectus.

  And yet Homo erectus looked very much more like us than any kind of bird. Is it fair to dismiss his works as the products of—for want of a better word—instinct? After all, Homo erectus is thought to have tamed and used fire.20 The discovery of stone tools at least a million years old on the island of Flores21 shows that Homo erectus was capable of crossing stretches of deep ocean out of sight of land—something that might well have involved a great deal of organization and planning. Yet we know that many animals less obviously endowed with intellect can cross stretches of open ocean by accident. In The Wisdom of Bones, a detailed look at the life and times of Homo erectus, Pat Shipman and Alan Walker conclude that Homo erectus would have had no more spark of what we might call “humanity” than any canny social savanna predator, such as a lion or a hyena. Studies on the development of Homo erectus teeth and skulls show that these creatures grew rapidly from infancy to adulthood, rather in the manner of apes, and lacked the extended period of growth called “childhood” during which a young modern human learns social skills from adults.22 To be sure, hyenas and lions teach their cubs about the ways of the world, and we might expect Homo erectus adults to have done the same. But that does not mean that the knowledge they imparted was any less hardwired, nor that the process of teaching and learning is not in itself stereotypical behavior.

  The million-year stasis of hand axes stands in stark contrast with the technology associated with Homo sapiens, especially after about 45,000 years ago when the first modern humans appeared in Europe.23 If the technology of Homo sapiens can be summed up in one word, it is “change.” Modern human technology is always changing and developing as humans learn from their mistakes, never discarding errors but learning from them to improve the old or invent something entirely new. In the light of modern human technology, the technology of Homo erectus is not technology as we understand it today—at least not conventionally.

  The shock one experiences when looking at a Stone Age cave painting or Venus figurine is that of recognition—that after millions of years of chipped pebbles and hand axes of unknown purpose, we can recognize the product of a mind that is distinctively human.

  And that’s a worry, because it introduces that inescapable referential bias that plagues any study to do with human evolution—that we are both the subject and the object of study, and will naturally know (or think we know) more about ourselves, and how our minds work, than of the minds of other creatures, including extinct hominins such as Homo erectus. It is only us, looking backward from our perceived high estate, that look at stone artifacts and immediately assume that they must have stemmed from the same creative, artistic, practical urges that we experience ourselves. That the motivations of Homo erectus might have been alien to our way of thinking seems an affront until one looks at the evidence dispassionately.

  Does this contrast—between the works of modern humans and those of Homo erectus—elevate human technology to some kind of special status? The constant change and invention that is typical of modern human technology seems to mark it out as something quite different from (say) a coral reef or a termite mound. Well, yes—and no. The change and invention is linked with the long childhoods of modern humans, but it remains the case that human children are taught, in much the same way as the young of other animals are taught, in a stereotypical way that is determined in part by the physical constraints of brain growth and development. For example, modern humans have an innate capacity for language—any language—without being taught in any conscious way, but must also be exposed to it at a certain time in infancy for it to develop properly. And the fact that we can’t grasp the purpose of the Homo erectus hand ax shows that despite its protean character, human technology is not infinitely malleable. It is fundamentally limited by our capacity for understanding or conceiving what is possible, according to our senses and how our brain interprets what they are telling us. We, like Homo erectus, have our boundaries. To us, they seem infinitely far away, over the intellectual horizon. But who’s to say that Homo erectus wasn’t similarly overoptimistic about his own limitations?

  It is entirely natural for us to think about our capacity to make beautiful things and on that basis ascribe to ourselves capacity for forethought that we deny every other living thing. I hope I have shown that this self-justification neither fits with a proper reading of evolution, nor is it fulfilled by the evidence. Unfortunately, our understanding of human evolution has become forever muddied by such self-aggrandizement. When Louis Leakey discovered the remains of a distinctive fossil human, which he called Homo habilis, “handy man,” the name was a direct reference to the discovery, in the same strata as the fossils, of very primitive stone tools. That Homo habilis had made the tools was not to be doubted, or so Leakey thought. The fact that remains of another extinct human, Zinjanthropus (now Paranthropus) boisei, were also found in these strata, was played down, because Paranthropus has a smaller brain than Homo habilis. The larger brain was meant to go with the tools. The tools must have been made by a large-brained creature, whose mind was stuffed full of what came to be called “planning depth.”

  This circular argument has been the source of no end of trouble, not least that the species itself was defined, in part, by a technology it was supposed to have created, when there was no certain way of linking tools and toolmakers. Ever since the 1960s, and with the discovery of more fossils of Homo habilis, people have worried about how to recognize fossils of Homo habilis should they find them,24 given that a defining feature of the species is a kind of behavior that not only does not fossilize, but which might not be unique to humans or the genus Homo. Some have even wondered whether Homo habilis should really be regarded as another form of Australopithecus.25 In recent decades, species such as Australopithecus garhi and Australopithecus sediba have been described as having some claim to close relationship with Homo.26 Australopithecus garhi, from Ethiopia, has at least as good a claim on the authorship of the earliest known stone tools as any member of Homo.

  It was the brain argument that was the real issue. Anthropologists looked a
t the skull of Homo habilis, painted it against the canonical picture of a progressive increase in brain size, and decided—retrospectively—that there was a brain size above which some kind of mental light would switch on, and the ape would become, if not an angel, then an artisan. The problem is that there is no simple connection between brain size and intelligence, a topic I’ll explore in the next chapter.

  9: A Cleverness of Crows

  If, after all that, I haven’t convinced you that there is nothing special about human beings that merits some elevated position on the top of nature’s tree, I know someone who might. That person is Nicky Clayton, professor of experimental psychology at the University of Cambridge and fellow of the Royal Society of London. She is the only Cambridge professor I know who arrives at work in a bright red dress and high heels. Scientist by day, dancer by night, she is an expert at the Argentine tango.1 And she spends a lot of time with birds of the family Corvidae—crows and jackdaws, jays and ravens. A single visit to Professor Clayton’s aviary should convince you that intelligence—if it stands for anything at all—is not confined to human beings.

  Clayton and her colleagues are learning to understand what goes on in the minds of nonhuman species. Corvids are excellent subjects. They are small, proverbially crafty, easy to keep in captivity, willing participants in experiments, often highly social, and there are lots of different kinds. This last means that results can be compared between species with different types of social behavior but equivalent apparent intelligence and brain size. This is something that can’t be done with humans, as we have no extant relatives that resemble us in intellectual facility or brain size. Whatever one means by “intelligence,” the great apes seem to have much less of it than humans. But they also differ markedly in social behavior from humans (and one another), as well as in brain size, which could both be factors. If apes were more sociable, or had bigger brains, would they be as “intelligent” as humans? Studying the variety of crow species—from ravens to jackdaws to jays to plain old crows—has the potential to adjust for the interaction (if any) between social behavior, brain size, and intelligence (and I’ll be returning to that subject, too). I suspect that we’d have a much more nuanced view of our own importance were Neanderthals or Denisovans still around with whom we could compare notes.

  In a long series of experiments, Clayton and her colleagues, as well as researchers elsewhere in the world, have shown how various species of crow are capable of many feats of intellect usually associated only with human beings. As I noted in the last chapter, the New Caledonian crow snips and shapes leaves to make tools every bit as useful as the probes chimpanzees use to extract termites from nests—or early hominins made for butchering meat. More remarkably, crows can use tools to make other tools to achieve a task.

  The cleverness of crows is proverbial. Everyone must have seen, by now, videos showing how crows leave nuts in roads, waiting for them to be cracked by the wheels of passing traffic—and the trick of those especially clever crows that leave nuts on pedestrian crossings, allowing the crows to retrieve the spoils without getting run over.2 In her lab, Clayton showed me a video showing how, when a crow is confronted with a morsel floating in a beaker of water but too deep for it to reach, the bird will use stones nearby to displace the water, raising the morsel to the surface and allowing it to be reached. To do this, the crow had to be able to appreciate the various properties of materials, such as that the food scrap floated, even when stones were thrown in the water; that stones would fall to the bottom; that stones displaced the water (equivalent to Archimedes’ “Eureka” moment); that the water would rise up the beaker, carrying the morsel of food. Not only that, the bird would have had some concept of itself throwing the stones into the water to achieve the desired outcome. So, not only can crows think things through, they are capable of thinking through what they are thinking through. And they are also capable of thinking through what other crows are thinking through.3

  To me, the most remarkable fact about crows is that theirs is a kind of intelligence that we can recognize—the calculation and the craftiness are things we see in ourselves. I do not think one is going too far by saying that the minds of crows work in a similar way to ours. In many ways, the human mind has more in common with the minds of crows than with our closest cousins, the apes.

  If this is true, it is remarkable, because crows and humans have brains that evolved entirely separately, along completely distinct pathways.4 The common ancestor of crows and humans was some kind of reptile that lived more than 250 million years ago, and would not have had enough brains to write home about. As a result, the human brain—and that of other mammals such as primates, dogs, whales, horses, and so on—is made rather differently from that of crows.

  This is an important insight in the context of this book because, once grasped, it shoots a huge hole in the idea that what we think of as the human mind must necessarily have evolved from earlier hominins simply by virtue of the fact that they were hominins, and had an evolutionary heritage that would have demanded progressive cognitive improvement in that lineage alone. It forces us to look at what we and crows have in common, to the exclusion of apes—and, from that, helps us understand the evolution of intelligence in general terms, not just in our own evolutionary lineage. All such similarities must very greatly be concerned with behavior rather than anatomy, as human brains and crow brains are wired differently, and crows don’t have the hand-eye coordination sometimes thought of as having been instrumental in the evolution of the human mind.

  What humans and crows (and many other birds) have in common is an active social life.5 Unlike apes, which are solitary or live in small groups, humans and birds tend to live together in large groups in which relatives of various ages mix together with less familiar individuals. They tend to learn from one another, but they are also competitive. They have a level of technological sophistication that outranks, in concept at least, anything seen in apes (even allowing for the fact that crows don’t have hands). Human and bird societies are cohesive and complex, and prone to a certain amount of internal discord and deceit. As I discussed earlier, cuckoldry is common in birds that are apparently monogamous, as it is in human societies, and this circumstance might, paradoxically, keep societies together, as birds will seek to keep an eye on not only the fledglings in their own nests, but those in the nests of their neighbors.

  There’s no doubt that the minds of crows are comparable in capability with those of humans, and have much the same flavor, for all that crows have no language, no hands, and brains the size of berries. A short visit to Clayton’s lab should dispel any notion that intelligence is necessarily all about brain size or hand-eye coordination. That we can recognize the same phenomena in creatures as distantly related to us as crows suggests that what we think of as intelligence might have less to do with the physical structure of brains in isolation, than with the complexities of social relationships quite irrespective of form. If we find intelligent aliens, we’ll recognize them, too. They’ll behave just like we do.

  Intelligence, however, does seem to have something to do with the mass of the brain relative to that of the rest of the body, irrespective of the brain’s actual size. This measure is called the encephalization quotient, or EQ.6 Animals with a high EQ have large brains relative to the size of their bodies. Crows have small brains, but they also have small bodies, so their brains tend to be relatively large compared with those of less clever birds of similar mass. That is, crows have a higher EQ than, say, pigeons or chickens. It is also true that human beings have a much higher EQ than mammals of comparable mass, and considerably higher than those of apes. Even bearing in mind the dangers of coming to a narrative, progressivist conclusion, the human EQ has increased rapidly and markedly over evolutionary time. Compared with those of apes, it is off the scale: the relative and absolute increase in brain size has been greater than for any other organ or organ system.7

  Not only is the modern human brain large, it consumes a di
sproportionate amount of energy. Even though it is large in proportion to our mass when compared with brain masses in other animals, it still constitutes only between a fiftieth and a hundredth of the mass of the body—yet it consumes one-sixth the energy. The brain’s expansion has distorted the skull so grotesquely that even though human babies are born in a relatively immature state, the hugeness of the infant’s head puts a mother’s life at risk. No doubt about it, the human brain is big. Bothersomely big. So it must be doing something. But what? What is the human brain for?

  By now you should be able to recognize that proposals of purpose should be treated with caution. Just because human brains are big does not in itself necessitate a simple explanation for such disproportionate size. Human brains might have evolved for better hand-eye coordination, for example—but that’s one of those circular explanations that I hope we’ve put behind us. In any case, work on crows disposes of that idea quite nicely—although quite a large amount of brain is devoted to coordinating the fine degree of dexterity of which human hands are capable, crows have large EQs and can make tools, and they must make do with their beaks.