The Accidental Species: Misunderstandings of Human Evolution (25 page)

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 defin
ing 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 at 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 disproportionate 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.

It is more likely that the human brain evolved to be as large as it is by virtue of a number of different circumstances that interacted with one another—sometimes reinforcing, sometimes opposing—over the
course of human evolution. The evolution of the human brain, like the evolution of anything else, must be thought about in terms of Darwin’s tangled bank, rather than the misreading of evolution as linear, progressive, and governed by purpose.

But first, to the brain’s bothersome bigness. A clue to why the human brain is so big can be found in the timing of human brain expansion in evolution.

It took off sometime after the evolution of
Homo erectus
but before the appearance of Neanderthals.
⁸
Significantly, this expansion occurred long after the invention of tools and technology.
⁹
When Louis Leakey and colleagues announced the discovery of
Homo habilis
in 1964, the whole idea of technology was linked with intelligence and brain size, leading to a long and fruitless discussion about the size of brain a fossil hominin ought to have before it could be considered either intelligent or technologically capable—as if, when the brain exceeded a certain size, a mental light would switch on and, like the apes in
2001: A Space Odyssey
confronted by a monolith, they would be catapulted into a new realm of cognition.

That period of prehistory—between 1.5 and 0.5 million years ago—is particularly murky. The world was inhabited by one or more species of hominin, collectively referred to as
Homo heidelbergensis
,
¹⁰
which presumably evolved into Neanderthals in Eurasia,
Homo sapiens
in Africa, and possibly other species in China and elsewhere. We know that
Homo heidelbergensis
individuals were big and beefy, which alone would have contributed to their large brain size. But we also know that they were technologically fairly accomplished. Well-fashioned wooden spears dating back some 400,000 years ago, and miraculously preserved in peat in Schöningen, Germany, were arguably made by
Homo heidelbergensis
.
¹¹
They look like well-balanced hunting javelins, but would have required a person of some stature to use them effectively. Another habit possibly started by
Homo erectus
and continued by
Homo heidelbergensis
was the controlled and deliberate use of fire, which would have led, very quickly, to the invention of the barbecue. As I discussed in the previous chapter, some have suggested that the invention of cuisine contributed in no small measure to the evolution of the large brain in humans.
¹²