THE MAKING OF THE MIND

The Neuroscience of Human Nature

Prometheus Books

Contents

Excerpt

CHAPTER 1

ORIGINS

The origin of the human mind is as lost as a grain of sand in the Sahara.It is impossible to say precisely when the psychological ingredients ofmodern human minds made their entry into the world because mindsdo not leave fossils that can be dated and interpreted by scientists. Today, wecan examine the living organ of the mind—the human brain—as it perceives,thinks, remembers, and imagines by means of the recently invented tools ofneuroimaging. Ancestral brains, on the other hand, turned to dust long ago,whether their owners once lived thousands, tens of thousands, or hundredsof thousands of years in the past. All that remain now are portions of theskull that once housed a human mind, or the bones of the legs that enabledupright walking, or the hands that enabled the crafting of tools or visual artistry.Although no one knows for certain when the modern human mind firstappeared, archeologists point to abundant evidence of its activity dating fromforty thousand to ten thousand years ago in the Upper Paleolithic or LateStone Age. By then, the mind within us was at work in the world creatingancient art of unmistakably human origin.

In the south of France, not far from Cahors, in the Midi-Pyrénées region, isa cave called Pech Merle. My visit there in the summer of 2005 was promptedby the chance to see prehistoric cave paintings created by early modernhumans. At first appearances, the cave at Pech Merle was indistinguishablefrom those limestone caves carved by water in the valley of the MississippiRiver back home in St. Louis. The crucial difference appeared only deep in thecave, far from the entrance, when the tour guide shined his flashlight on a walladorned with hauntingly beautiful images of human hands and spotted horses.These and many other images in the cave were created by human beings inthe Upper Paleolithic era of prehistory. Using carbon 14 dating, archeologistsestimate the age of the spotted horse at about 24,640 years old.

Because of the location of the painting in Pech Merle, it can be inferredthat the artist or artists had specific memory abilities well known in contemporarycognitive neuroscience. The artist responsible for the spotted horseshad to retrieve an image of a horse from long-term memory and maintain itin a temporary store referred to as working memory. By comparing a visual-spatialrepresentation in working memory with the image unfolding on thecave wall, the artist would have been able to create an accurate representation.Because the work was done deep in the cave, the model for the drawing wasnot present in visual sight. Indeed, the artist had to work from some kind oftorch light to even see the creation underway. Conceivably, the artist mighthave been recollecting a specific horse seen at some point in the past, using acapacity for mental travel back in time, or it may have been a more generalmemory of the concept rather than a specific instance. Alternatively, perhapsthe artist was simply imagining a horse that could have differed from anyspecific horse ever before encountered. Cognitive anthropologists have in factwondered whether the images were a product of the hallucinogenic imageryof a shaman. Although it had been thought by biologists that wild, pre-domestichorses had only coats of black or bay, the spotted pattern found in theimages of Pech Merle in fact were painted from memory rather than fantasy.The genes responsible for the spotted-leopard pattern found in some modernhorses were also identified in DNA samples of horse remains in WesternEurope dated to the Pleistocene, the geological epoch ending ten thousandyears ago, just prior to the Holocene epoch of today. The same pattern was notfound in Asian samples from the Pleistocene, suggesting that all horse colorsobserved in Paleolithic art in fact were found in the prehistoric horse populationswhere the caves were located.

The artwork of the Upper Paleolithic provides vivid evidence of a modernhuman mind. It indicates that modern humans were living in Europe by fortythousand years ago, although they likely originated earlier in Africa, as willbe discussed later in the chapter. The makers of the cave paintings and carvedfigurines were fellow members of Homo sapiens just like us today. Archeologistshave discovered thousands of pieces of Paleolithic art rendered on limestonecave walls as well as small objects of stone, bone, antler, and ivory that areassociated with the fossils of human remains. Although such artwork has beenfound in several parts of the world, the most intensively investigated and well-knowncollection comes from southwestern Europe. In the cave at Lascaux insouthern France alone, for example, more than fifteen hundred images adornthe walls. Animals are a frequent subject matter, but images of humans, andanthropomorphic-type images that combine parts of an animal (e.g., antlers)with a human figure, are also common. Abstractions in the form of geometricsigns are also observable. Unmistakably, the creators of these works werecapable of using visual symbols to represent ideas.

During the Upper Paleolithic, there is clear evidence of an explosion ofcultural creativity. Besides the cave paintings and sculptures, archeologistsdocument an increased sophistication in tool making and weaponry, and awide variety of body adornments. This explosion of Upper Paleolithic culturehas been referred to as a "human revolution" or the "dawn of human culture"or "a great leap forward" as a way of highlighting the discontinuity with theartifacts produced by earlier members of the hominid lineage. For example,neither Homo neanderthalis nor Homo erectus left artifacts comparable in theirsophistication, variety, and sheer number as those created by Homo sapiens.Scholars disagree as to whether the change to the modern mind was as suddenas implied by the concept of "a great leap forward" or instead reflected agradual accumulation of changes starting back even further in the past. Ineither case, by forty thousand years ago humanity had crossed the Rubicon,setting the mind within us apart from all other creatures. How is the humanmind so fundamentally distinctive? The aim of this book is to provide a novelanswer to this question by drawing on contemporary research in cognitivesocial neuroscience.

By analyzing what has been learned in recent decades about the neuroscienceof our cognitive and social abilities, it is possible to identify the mostimportant distinctive features of the mind within us. Major advances havebeen made with the invention of tools, such as functional magnetic resonanceimaging (fMRI), that allow one to infer neural activity as cognitive functionstake place in the living brain. Importantly, the brain of a twenty-first-centuryhuman being has the same structures and distinctive cognitive capacities asthe brain of the Upper Paleolithic artist. It was this brain—the one we caninvestigate today with the tools of contemporary neuroscience—that enabledus to invent culture and exploit cultural change over relatively brief periods ofhistorical time. The capacity for logical inference exhibited by the scientistswho analyzed the DNA of horses to draw conclusions about the cave paintingsof the Upper Paleolithic was already present in the prehistoric originatorsof the art. In like manner, the capacity for planning that enabled humans inthe twentieth century to land on the moon was already manifest in our prehistoricancestors. As the noted paleontologist Stephen Jay Gould observed,"Cultural change has brought most of us through hunting and gathering,past the explosive new world triggered by agriculture, and into the age ofatomic weaponry, air transportation and the electronic revolution." This culturalchange was brought about with "the same brain that enabled some of usto paint the caves of Chauvet and the ceiling of the Sistine Chapel."

Evolutionary theorists explain the constancy of the human brain overthe past forty thousand years in one of two ways. The classical Darwinianview of gradual change over vast periods of geological time holds that tensof thousands of years is insufficient time for significant biological change tooccur. A different view, and the one favored by Gould, is that species typicallyremain static in form over tens of thousands of years with no gradual changeat all. When a new species emerges through natural selection, speciation takesplace relatively rapidly—as a saltation rather than a slow gradual accumulationof differences. The abrupt transition associated with the formation of anew species is then followed by a new equilibrium where no change at all isobservable for long periods of time. This alternative to Darwinian gradualismis called the punctuated equilibrium model of evolution. In any event, theessential point for the thesis of this book is that we can understand the causesof the "human revolution" during the Upper Paleolithic by investigating thebrain and mental capabilities of modern human beings alive today. With therecent advances in the cognitive sciences fueled in part by the invention oftechnology for imaging the living brain, it is now possible to outline why themind within us is so distinctive.

The premise of stasis in the fundamental distinctive features of the humandoes not conflict with the fact that some simple adaptations have occurred overthe past ten thousand years. For example, with the invention of agricultureand the domestication of cattle in the final Neolithic phase of the Stone Age(8000–9000 BCE), a dietary adaptation occurred to allow the consumption ofmilk during adulthood. The hunter-gatherers of prehistory needed the lactaseenzyme required to digest milk early in life while nursing, but then it wasturned off during maturation. A mutation in the gene responsible for turningoff the production of lactase allowed even adults to consume milk, an adaptationthat eventually spread widely among Europeans. The kind of adaptationsthat resulted in the modern human brain—something akin to addingwings with which to fly—were far too complex to occur rapidly in thousandsof years. An example is the human capacity to innovate and plan new ways ofliving, as was required for the invention of agriculture in the first place.

THE ENSEMBLE HYPOTHESIS

One straightforward and common answer to the mystery of "human revolution"is that the brain expanded or reorganized symbolic thought. Symbols arecertainly evident in the cave paintings in the form of representational art.A visual symbolic representation is used to refer to a horse, a bull, a deer,a bison, or another human being. A capacity for symbolic thought couldhave facilitated the ability to think about abstract concepts that are not tieddirectly to perceptual experience. Closely related to this hypothesis is that thebrain expanded or reorganized to support language, where words are used assymbolic representations, and the use of visual-spatial symbols. If either ofthese hypotheses is correct, then there should be evidence from neuroscience ofan obvious change in the brain from nonhuman to human species. Or, comingat the question from the level of the genes responsible for the development ofthe brain, there ought to be a mutation in a gene or set of genes that accountsfor the distinctive feature of human brain maturation related to symbol useor language.

The thesis of the present book adopts a related but more complex pointof view. The argument here is that there was not a single major addition to orreorganization of the brain and cognitive functioning in the advent of modernhuman beings. Instead, the findings of cognitive social neuroscience documentthe addition of five parts that together comprise the modern mental ensemble.Each part reflected a reorganization of the brain of our immediate hominidancestors—in some cases this reorganization could have been relatively minor,such as an advance in the executive functioning of working memory; in othercases, the reorganization probably was more significant, such as in the stepto using abstract symbols in thought rather than concrete perceptual representations.The central point is that changes occurred on multiple fronts,from small to moderate. Looking at each part in isolation, it might have beenpossible to discern with ease the continuity with (and specific nature of) thechange from our immediate ancestor, had the evidence not long ago turned todust. But small to modest changes took place on several fronts. This certainlymeant that a greatly expanded brain needed to accommodate the sum of thechanges. Besides a change in brain quantity, a profoundly important changein quality also occurred because each part interacted with one or more otherparts. The parts must be considered together, with each understood only inrelation to the whole. The ensemble hypothesis contends that the interactionof the parts, not just the increase in brain size, yielded the dramatically differentmind within a modern human.

Here human symbolic thought and language are viewed as so closelyinterwoven as to constitute just one of the five key parts. Contemporaryresearch in the neurosciences has extensively documented four others that arecrucial for the ensemble. One is an advanced working memory, particularlythe executive functions that enable planning and self-regulation. Another isan advanced social intelligence that enables humans to collaborate, empathize,and transmit culture from one generation to the next through imitation andother means of social learning. The next part involves a modification of languagefor the purpose of silent thought rather than vocal communication. Aslanguage became interiorized as inner speech, it combined with a capacity tomake causal inferences. This part is called the interpreter because it explains thecontents of our conscious experiences. Lastly, long-term memory in humansunderwent a specialization in the ability to recollect specific episodes from ourpast experience. This episodic form of long-term memory allows one to recallwhat, when, and where a specific event occurred. Further, it allows one toimagine an event occurring in the future using the same mental capacity. Forthis reason, the fifth and final part of the ensemble is referred to as mental timetravel. The modern human mind can roam into the past of our autobiographicalexperience or venture forward in the imaginary future with equal ease.

When considered in isolation, it should not be surprising to see substantialevidence of the precursors of these five distinctive parts in species withwhich we share a genetic history. Because the modern chimpanzee is the onlyliving species with a relatively high degree of similarity in its genome toHomo sapiens, neuroscientists are especially interested in comparisons betweenthe two species. As will be seen later in the chapter, such comparisons are oflimited value because human beings are not descended from modern chimpanzees.Homo erectus is hypothesized to either be a direct ancestor of modernhuman beings or a close side branch of the human lineage; it is in any caseextinct and known only from the evidence of paleontology and archeology.Homo neanderthalis is another extinct hominid, but one thought to have coexistedwith modern human beings recently enough to have left behind DNAsamples for geneticists to study. Neither DNA nor fossilized skulls tell us howthe brain was organized, however. It is impossible to compare, then, the brainof an immediate ancestor or close hominid relative with the brain of a modernhuman being.

So, for better or worse, comparative neuroscience does what it can andcontrasts the brain and cognitive abilities of chimpanzees with those of humanbeings. If the ensemble hypothesis is correct, then it should be expected that,say, working memory ought to show continuity between a chimpanzee and ahuman being. Although the executive functions of human working memoryare more advanced than those of a chimpanzee, the differences ought to bea matter of degree rather than of kind. Conceivably, the summation of allfive parts yielded a human mind that is distinct in kind from a chimpanzee'smind, but that is debatable. According to the ensemble hypothesis, however,the summation of five parts is only the beginning of what sets the mind withinus apart. It is the interaction of two or more parts that yields a qualitativelydifferent kind of mind.

The "human revolution" came as a result of a nonlinear discontinuity withancestral species, according to the ensemble hypothesis. Advanced workingmemory is only one of the five parts in the ensemble. The other parts eachadded their own distinctive features, and critically, they interacted with eachto yield a new kind of mind in Homo sapiens. Thus, the human mind is morethan the summation of an advanced working memory plus an advanced socialintelligence. The interaction of these two parts alters mental functioningbeyond their linear combination. As language, the interpreter, and mentaltime travel add to the ensemble, the human mind diverges sharply and discontinuouslyfrom all nonhuman forms, despite the fact that each individualpart shares similarities with that of the nonhuman counterpart. Even thougheach of the brain reorganizations underlying the components of the ensemblecould have been relatively minor compared with an immediate ancestor, thewhole of their ultimate effect would be unpredictable from looking at each ofthe parts. Thus, when considered as an ensemble, the human mind inhabits amental world on earth with one and only one member.

What exactly is meant by nonlinear discontinuity? The critical conceptat the heart of the ensemble hypothesis is a statistical interaction of two ormore independent factors that have an effect on brain or cognitive complexity.Advanced working memory increases cognitive complexity. So, too, doesadvanced social intelligence. Both of these operating at once in the modernhuman brain could increase cognitive complexity in an additive way—the netresult may be simply a linear combination of each factor taken separately. Yet,according to the ensemble hypothesis, there is a two-way interaction of factorsthat yields a nonlinear combination of their independent effects. The powerof an advanced social intelligence to boost cognitive complexity is enhancedby the presence of an advanced working memory. Similarly, the power of symbolicthought and language to boost cognitive complexity is impressive on itsown merits. Even so, when combined with an advanced social intelligence atthe same time, the result is a nonlinear discontinuity from nonhuman mindsthat possess less powerful social intelligence and modest to minimal symbolicthought and language capabilities. Analogous cases can be made from pair-wiseinteractions of all five parts of the ensemble hypothesized here.
(Continues...)Excerpted from THE MAKING OF THE MIND by RONALD T. KELLOGG. Copyright © 2013 by Ronald T. Kellogg. Excerpted by permission of Prometheus Books.
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