Masters of the Planet (38 page)

We are, then, confined for the moment to static aspects of the brain in our search for the biological underpinnings of what makes us unique. And although it's long been known that there are few if any gross aspects of the human brain without their counterparts in apes, significant differences in tissue architecture are beginning to emerge as neurobiologists look at ape and human brain materials in finer and finer resolution. One recent discovery is that, while apes and humans as a group are unique in having “spindle” neurons in parts of the brain that in humans are involved in complex emotions such as trust, empathy, and guilt, we have many more of them. Scientists aren't yet sure exactly why this is, but one possible function for spindle neurons is in aiding high-speed conduction of impulses from these regions to an area at the front of the brain concerned with advance planning. It may be that the abundance of spindle neurons helps humans make swift responses to complex and changing social situations. As more and more findings such as this come to light, we will certainly be able to put together a more complete picture of what happens in human brains that doesn't in others. But for the moment, while we can be confident that the behavioral advantage humans enjoy does not simply emanate from a greater mass of brain tissue, the best we can do is make educated guesses.

My personal favorite conjecture is still the one made by the great Columbia neurobiologist Norman Geschwind back in the 1960s. Geschwind's notion was that the discrete identification of objects—naming them—was the foundation of language. Using the connection I'm making here, it would also be the foundation of symbolic cognition. In Geschwind's view, language was made possible by a physical ability to make direct associations between different areas of the brain's cortex,
without
passing through the older emotional centers below. The cortex is the thin sheet of neural cells that covers the outside of the brain, and it has so greatly expanded during mammal evolution (and especially in us) that, as we've seen, it has become creased and folded to fit inside the confines of the cranial vault. The largest of the folds have been used to demarcate various major functional areas of the cortex, notably its frontal, parietal (upper side), temporal (lower side), and occipital (back) “lobes.” Within each lobe, other wrinkles demarcate major functional areas. Thus Broca's area, that brain region which plays a key role in motor functions including control of the speech apparatus, lies within the left frontal lobe. Modern imaging techniques have shown that many motor and other functions are in fact widely distributed through the brain; but nonetheless the major control areas identified by the great nineteenth-century neurologists are still recognized today. And most modern neuroscientists are comfortable with the idea that the prefrontal cortex, right at the forward tip of the brain, is particularly crucial in the integration of information coming in from all over this hugely complex organ. It is clearly the seat of the higher “executive” functions, coordinating and regulating the activities of the phylogenetically older parts of the brain.

But Geschwind's particular candidate for the structure permitting the associations crucial in object-naming was the “angular gyrus,” a part of the parietal lobe that lies adjacent to both the temporal and the occipital areas, and is ideally positioned to mediate among all of these lobes. In humans the angular gyrus is large, whereas in all other primates it is small or missing altogether. What's more, recent imaging studies have demonstrated that it is active in the comprehension of metaphors, which are emblematic of the kind of abstract connections that are basic to language. Whether Geschwind was right or wrong, it is thus frustrating that it is next to impossible to delineate the angular gyrus in endocasts of fossil hominid brains, so we simply don't know at what point in our history it started to expand.

In figuring out just what it is that makes our brains special, we always have to keep in mind that our controlling organ is a rather untidy structure that, from very simple beginnings, has accreted rather opportunistically over an enormous period of time. So perhaps we shouldn't
be
looking for one single major “keystone” acquisition. Instead, the extraordinary properties of the human brain are likely emergent, resulting from a relatively tiny—and altogether accidental—addition or modification to a complex structure that was already, and exaptively, almost prepared for symbolic thought. A small tweak to an existing—and independently viable—structure gave rise to a new form of interaction among the brain's constituents that gave it an entirely unprecedented level of complexity in function.

If we can't pinpoint any specific brain
component
as the basis for our modern human consciousness, we might ask about which cognitive
systems
might have been involved. One favorite system that has been getting a lot of play recently has been our working memory, the term used by psychologists to denote our ability to hold information in the conscious mind while undertaking practical tasks. Without substantial working memory it would be impossible for us to carry out any kind of operation that involved associating several different bits of information. Proponents of the idea that working memory most crucially underwrites our complex activities do not deny that ancient hominids also needed a certain amount of such memory; but they suggest that the difference between us and them, though substantial, is one of degree, related to increasing refinement of those executive functions of the prefrontal cortex that govern decision-making, goal forming, planning, and so on. As we've seen, the various technologies that hominids developed since the inventors of stone tool making first bashed one stone with another became more complex in a highly sporadic manner. And this has been taken as evidence that working memory increased in stepwise fashion, the last major step being taken somewhere between 90 and 50 thousand years ago.

This scenario certainly fits with what the archaeological record seems to be telling us. But it still leaves the question open as to whether working memory is merely a necessary condition of our modern consciousness, rather than an altogether sufficient one. When we are pondering how we acquired our odd way of doing mental business, we might do well to consider that identifying working memory as the key ingredient to our uniqueness may in fact be analogous to selecting thermoregulation, or distance vision, or object-carrying, as the key factor that caused the earliest hominid bipeds to stand upright. The reality is that once you have the capacity concerned you have bought an entire package of advantages, plus any disadvantages that might come along with it. In the case of bipedality, standing upright was almost certainly just what came naturally to the creatures involved. In the case of symbolic consciousness, it seems likely that a random modification of the already exapted brain, plus some children at play, led to the literal emergence of a phenomenon that changed the world.

CODA

None of what I said at the end of
chapter 14
implies that our species has necessarily changed our planet in an intentional way. It's certainly reasonable to suppose that there was no such intention at the start, in a world where our forebears were hunters and gatherers: people who were largely, if not entirely, integrated into their ecosystems. It is, though, highly probable that from the very beginning, apart from death, the only ironclad rule of human experience has been the Law of Unintended Consequences. Our brains are extraordinary mechanisms, and they have allowed us to accomplish truly amazing things; but we are still only good at anticipating—or at least of paying attention to—highly immediate consequences. We are notably bad at assessing risk, especially long-term risk. We believe crazy things, such as that human sacrifice will propitiate the gods, or that people are kidnapped by space aliens, or that endless economic expansion is possible in a finite world, or that if we just ignore climate change we won't have to face its consequences. Or at the very least, we act as if we do.

All of this is, of course, in perfect agreement with the untidy accretionary history of the human brain. Inside our skulls are fish, reptile, and shrew brains, as well as the highest centers that allow us to integrate information in our unique way; and some of our newer brain components talk to each other via some very ancient structures indeed. Our brains are makeshift structures, opportunistically assembled by Nature over hundreds of millions of years, and in multiple different ecological contexts. When we realize that our symbolic capacities are an incredibly recent acquisition—and not merely the icing on the cake, but the candy bead surmounting the cherry atop the icing—it becomes evident that our
brains
as they perform now cannot have been fine-tuned by evolution for anything. We have achieved our mental eminence only because a long series of ancestors, stretching back into the most remote reaches of time, happened simply to have been able to cope with prevailing circumstances better than their competitors could. And then a final, still inscrutable, acquisition just happened to make a huge difference. If anything had occurred otherwise, anywhere along that lengthy trail, you wouldn't be reading this book today.

There is a school of thought that we humans sometimes act so bizarrely because the evolution of our brains has not been able to keep pace with the rapid transformation of society that has occurred since humans began to adopt settled lifestyles at the end of the last glacial episode. Our minds, according to this view, are still responding, sometimes inappropriately, to the exigencies of a bygone “environment of evolutionary adaptedness.” This view has a wonderful reductionist appeal; but in reality our brains are the ultimate general-purpose organs, not adapted “for” anything at all. Yes, you can indeed find regularities in human behaviors, every one of them doubtless limited by basic commonalities in the structure of our controlling organs. But all such regularities are in reality statistical abstractions, and people are absolutely uniform in none of them. As a result, if any statistical phenomenon could be said to govern the human condition, it would be the “normal distribution,” or the “bell curve.” This describes the frequency with which different expressions of the same feature occur within a population. Tall in the center, where most individuals cluster, this bell-shaped curve tails off more or less symmetrically to each side, reflecting the fact that most observations of any feature fall close to the average, with deviations becoming increasingly rare the farther they lie from the mean.

In any human characteristic you might care to specify, physical or behavioral, you will find a bell curve. Only a few of us are very smart, or very dumb; most of us are somewhere in the middle. Ditto with tall/ short, caring/indifferent, strong/weak, chaste/promiscuous, spiritual/ profane, or any other continuous variable you might care to mention. This is, of course, why the internal human condition is virtually impossible to pin down: you can easily find an individual
Homo sapiens
to exemplify each extreme of any behavioral spectrum you can dream up.
For
every saint, there is a sinner; for every philanthropist, a thief; for every genius, an idiot. In this perspective, having bad people around is simply the price we pay for having good ones as well. Put another way, there is no need to look for special explanations for altruism when this feature is matched on the other side of the curve by selfishness. Individuals themselves are typically bundles of paradoxes, each of us mixing admirable with less worthy traits, even expressing the same trait differently at different times. We are ruled by our reason, but only until our hormones take over.

Similarly, nobody subscribes to
all
of those crazy ideas that are floating around, though most of us are attracted to a few of them. One of those crazy ideas is that the human condition can somehow be described by a long laundry list of “human universals”—uniquely human psychological and behavioral features that everybody has. But it nearly always turns out that these “universals” are either not uniquely human, or not universal among humans. Indeed, apart from that basic ability we all share to re-create the world in the mind, perhaps the only other true “human universal” we all show is cognitive dissonance.

Because of its peculiar cognitive properties, our species and its individual members are entities of entirely different kinds. For, while individual human beings are substantially—though not entirely—the products of their own particular genomes, coming into the world as broadly the kind of persons they will be as adults, this is not true in the same way for the human species as a whole. Indeed, the universal human condition will always remain elusive (and incessantly debated) for the very good reason that it is inherently unspecifiable.

So, what are we to make of ourselves? After a long evolutionary history we have arrived at a point at which our accidental cognitive prowess is allowing us unwittingly to change the very surface of the Earth on which we live. Indeed, it has recently been proposed (with typical human arrogance) that we should rename the current Holocene epoch of geological time the “Anthropocene” (roughly, the “new human age”). Many geologists cringe at this suggestion (the invention of an ecologist and an atmospheric chemist) because the depredations of a single species have never been used as a criterion for defining a phase of geological time. Nonetheless, it is nothing short of alarming how human intervention is
affecting
a huge array of processes that will clearly be reflected in the record available to future geologists, should there be any. To take just one example of many, over the eons all the natural might of the elements has typically lowered the surfaces of the continents by a few tens of meters per million years. In shocking contrast, a recent analysis has shown that trends in human activity that started only around the beginning of the first millennium have led to a current rate of worldwide erosion that is ten times higher.