The Making of the Mind: The Neuroscience of Human Nature (8 page)

Delaying the impulse for immediate gratification requires an effortful inhibition of these urges, thus draining some of the limited supply of executive attention. If given the choice of a small immediate reward versus a much larger reward later, fully mature human beings have the capacity to delay gratification and gain the advantage of the larger reward. The prefrontal lobes and executive capacity develop only slowly during childhood and adolescence. It should not surprise us, then, that adults often make different decisions about taking risks to seek gratification than they did when in their youth. Further, those who develop strong executive control early in life tend to be more successful later in life. For example, preschoolers have been assessed in their ability to wait for a treat of two marshmallows that was superior to the one marshmallow available to eat immediately. Strikingly, the number of seconds that these young children were able to resist the impulse of immediate gratification predicted their ability to concentrate as an adolescent. It also predicted their ability as adolescents to deal with frustration and temptation.
The longer children could wait for the larger reward as a preschooler, the more likely they were to be judged as both academically and socially competent as adolescents.
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Delaying gratification is a very simple example of planning ahead or thinking strategically. More complex planning is essential to all problem solving. From where one now stands a series of steps must be taken that lead to a goal. Planning allows the problem solver to think one step or perhaps several steps ahead. It allows the problem solver to simulate in working memory—by talking about the plan covertly through inner speech or by imagining scenes in a visual-spatial format—all of the things that could go wrong when a step is taken in a particular direction. The human ability to hold different scenarios in mind and to try out different possible paths to the goal thus depends on executive attention.

Although human beings are superior in executive control compared with other species, it must be remembered that the resource of executive attention is limited in us all. It can readily be fatigued by constant demands, for example. Individuals with lower capacities of executive attention have more difficulties in coping with the incessant need for self-control of impulses. Moreover, the larger the capacity to attend to mental representations and maintain them in working memory, the better one can comprehend speech, read, write, reason, solve problems, and think in general. These mental skills are collectively assessed by a test of general fluid intelligence. Scores on such tests can be accurately predicted by knowing the capacity of executive attention.

Cognitive psychologists have devised a test to measure individual differences in how well one can update the contents of working memory, shift between two tasks, and inhibit old irrelevant information. The test involves two tasks that have to be performed concurrently. A mental arithmetic problem is presented first, followed by a word. The test takers calculate the answer to the arithmetic problem and then shift attention to storing the word in working memory. Then another arithmetic problem and word are presented. After several of these trials, the person must try to recall all of the words that had been presented up to that point. Individuals with a large capacity for storing the words in verbal working memory, and, most importantly, a large capacity for executive control, can remember the most words
correctly after correctly performing each arithmetic problem. Scores on this test of executive attention and working memory storage correlate moderately to strongly with general fluid intelligence.
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Fluid intelligence refers to the ability to solve novel problems. It differs from the breadth and depth of knowledge that a person has learned and stored in long-term memory—a construct known as crystallized intelligence. Although both forms of intelligence are important for human beings, the capacity to solve novel problems provides the engine of innovation that propels cultural evolution. It is notable, then, that the capacity of executive attention is such an important determinant of fluid intelligence.

Neuroimaging of the human brain while it solves novel problems taken from standardized tests of fluid intelligence has revealed portions of the network of executive attention. For both verbal and spatial novel problems that require a high degree of fluid intelligence, the lateral region of the prefrontal cortex in the left hemisphere showed strong activation.
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Thus, the massive frontal lobes of the human brain provide an abundance of cortical space for the support of an advanced system of working memory and, in particular, its central executive component. The extended juvenile period that characterizes human development provides an extended period for pruning synapses in the frontal lobe of the brain and for completing the myelination of neural axons that allows for highly efficient neural networks. Metaphorically speaking, the executive suite of the human brain is well furnished by the time it takes one to reach young adulthood. The adult human brain allows a level of executive control that is never attained at all in other primate species. In commenting on comparative research with mature rhesus monkeys, for example, Michael Posner and Mary Rothbart observed that the “results of the tests with monkeys seemed more like those of young children whose executive attention is still immature than like those of adult humans.”
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Human beings eventually develop a capacity for delaying gratification, inhibiting inappropriate behaviors, and planning solutions to complex novel problems.

The human capacity for fluid intelligence—the ability to solve novel problems—is of particular importance in understanding the unique cultural world in which we live. Human beings stand apart from other species in our
capacities for behavioral innovation and the cultural transmission of those innovations from one generation to the next. It has been argued in the present chapter that an advanced form of working memory is critical for the innovation part of this equation. In the
next chapter
, the advanced form of social intelligence found in human beings will be addressed. Although human beings have attained a highly advanced form of both working memory and social intelligence, there is nonetheless evidence of continuity with other primates with respect to both. Instances of behavioral innovation have been observed in numerous primate species—this refers to behaviors observed in the field or in captivity that were never seen before, as opposed to traditional behavior patterns of the species. Examples of social learning have been documented as well. By tallying the frequency of such instances of innovation and social learning across different species of primates, it was possible to examine the relation of both to brain development.
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The volume of the neocortex and striatum taken together provided an index of what the researchers called the “executive brain.” This reflects in part the sheer amount of cortical capacity available for executive attention and the other components of working memory in nonhuman species. Because primate species differ widely in body and overall brain size, the executive brain ratio was computed by dividing the neocortex and striatum volume by the volume of the brainstem. In essence, the executive brain ratio calibrates the extent to which the forebrain can support an advanced working memory and advanced social intelligence. The researchers found a significant positive relationship between the executive brain ratio and both innovation and social learning. In fact, innovation and social learning were also correlated with each other, indicating that the two are not entirely independent of each other. Thus, even while confined to nonhuman primates, there is a clear relation between the amount of cortex that supports the executive functions of working memory and the likelihood of engaging in novel behaviors or learning behaviors from observing others.

In sum, the executive function of human working memory is highly advanced, and it undoubtedly played an important part in the emergence of the modern human mind. Another major change is the addition of a phonological loop specialized for the learning of language. Yet continuity with nonhuman species is also not difficult to discern. Primates in general, including
even the relatively small-brained rhesus monkey, make use of the prefrontal cortex for the temporary storage of stimuli that are currently out of sight. Baboons are severely limited to storing only about four chunks of information in the visuo-spatial sketchpad of working memory, but then so are human beings. Although human beings possess a much larger frontal lobe than other species, it is not larger than what would be expected for a great ape with a similar overall brain size. Thus, it is not relative space allocation but rather the connectivity of the brain's neural circuitry that appears to be where a reorganization of the frontal lobe took place in the transition from nonhuman to human. The puzzle piece of working memory appears different in human beings than in our close genetic neighbor, the chimpanzee, but not unrecognizably so. It is when the piece is put together with other parts of the modern ensemble that a qualitatively different kind of mind emerges. One example of this interaction has already been described with the addition of the phonological loop in human beings as an adaptation for the learning and use of language.

The second part of the ensemble of the modern mind is an advanced social intelligence that enables human beings to invent—through active collaboration—the language, beliefs, behavioral practices, and societal traditions that envelop us in our social environment. The innovations made possible by an advanced form of working memory alter the natural world into a social and technological environment of our own design. The cultural world that we invent serves as communal glue that binds us together with common values and ways of living. It invades the brain from the moment of birth, creating a mind shared by many. It is information as valuable to pass on to the next generation as the genetic information encoded in DNA. Just as DNA transmits the traits of our parents and direct ancestors forward to us, so, too, does the culture of “our people” replicate and survive into the future. The advanced social intelligence of human beings provides us with the tools to observe others and imitate their behavior. Through these tools, the mantle of culture is passed from one generation to the next.

Besides providing the means for the inheritance of culture, our advanced social intelligence enhances our capacity to innovate new ways of living. It opens us to the possibility of collaboration among individuals for mutual gain, rather than relying exclusively on competition for self-survival. In
Homo sapiens
, individuals both learn from each other and work together to solve common problems. Through such collaboration, the power of human fluid intelligence to innovate is leveraged many times over. The executive functions of working memory provide the ability for any human being to solve a novel problem. But imagine multiplying that ability by five, ten, or twenty times as
groups of human beings collaborate together. Here, then, is a prime example of an interaction between two parts of the modern mental ensemble. From this interaction, innovations flourished and were socially transmitted from one group of human beings to another, and especially from one generation to the next. Rapid innovation plus cultural inheritance released human beings from the glacially slow pace of biological evolution. Tens of thousands, if not hundreds of thousands, of years were no longer needed for dramatic changes in the functioning of the human mind. Through an advanced social intelligence and its leveraging of fluid intelligence, human beings were launched onto the fast track of evolution—the evolution of culture rather than genes.

Culture—the words used to refer to ideas and events, the political and religious beliefs, the preferences for clothing and food, and thousands of other practices and traditions—sets us in a different world from all other species. We simultaneously inhabit a physical world—one we certainly share with chimpanzees—and a cultural world, which is reserved for the human mind. Human beings swim in culture in much the way fish swim in water. Culture surrounds us, and we breathe it in as a kind of mental oxygen. It is the sum total of the human way of life, accumulated through history and inherited from generation to generation since the Stone Age. People living in close proximity in a group often develop common beliefs about the world, just as they come to share food preferences, clothing styles, means of adorning the body, tools, and language. The group finds common ground for social interactions among its members and expectations of what is normal and what is deviant. Such norms provide the social glue that holds the group of people together.

Because culture is everywhere in our lives, it is generally invisible to us, so taken for granted as to be imperceptible. But such transparency can quickly turn opaque when human beings migrate from one part of the world to another. Imagine an American raised on a farm in rural Kansas transplanted to the Asian metropolis of Shanghai. Or imagine the life-long New Yorker relocated to the remote mountains of Afghanistan. For immigrants, the pain of separating from family, friends, and the country of one's childhood is compounded by the uncertainty and novelty of the adopted land.
Culture shock
aptly captures the disorientation of being dumped from familiar to foreign
cultural waters overnight. The immigrant must acclimate to the strange waters and learn to swim again in the new culture. Travelers, too, experience culture shock, although only temporarily while visiting a foreign country before returning to the familiarity of home.

Human beings are a richly diverse species. The differences among human populations, however, are much less a matter of genetic differences and much more a matter of cultural differences. The sounds we utter, the clothes we wear (or, equally significant, do not wear), the food we eat (and the way we eat it), the rules we follow in living together, and the beliefs we hold about government, health, ethics, religion, destiny, and all else in between separate us from one another in ways that our genes do not.

A definitive feature of the human mind is our massive addition to the physical world of things that we need or imagine we need. For example, the human capacity to make tools, from prehistoric stone tools to the machines of the twenty-first century, has transformed the physical landscape. The invention of agriculture prior to 4000 BCE laid the foundation. The invention of industry in the late nineteenth century yielded a massive expansion of artifacts to satisfy the material, psychological, and spiritual needs of human beings. The globalization of industry, driven by technological innovation, in the late twentieth century vastly accelerated the process. Buildings, furniture, appliances, books, blogs, paintings, photographs, sculptures, graffiti, musical scores, telephones, cell phones, Blackberries, iPods, iPhones, desktop computers, laptop computers, and plastic containers in every conceivable shape and size, are now as much a part of the biosphere as plants and animals.

THE FAST LANE OF EVOLUTION

The cultural practices of modern human beings in the Upper Paleolithic or Late Stone Age of thirty-five thousand to eight thousand years ago have been deciphered by archeologists using evidence from human artifacts dated to the time period. As discussed in
chapter 1
, the cave paintings and engravings of the Cro-Magnon people of southern France provide an example of such evidence, and similar images of rock art have been found in nearby Africa and in distant Australia. Such art first emerged during the Upper Paleolithic, and it marked
the advent of the modern human mind. The number, variety, and sophistication of tools, weapons, and bodily adornment also exploded.
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Most significant for the point made here is that the rate of cultural change began to accelerate during the Upper Paleolithic, and it accelerated still more in the Neolithic period, continued unabated into the ancient world, and today overwhelms us with scientific and technological innovation almost on a yearly basis.

Early modern humans lived as roving bands of hunters and gathers, a means of survival that dates back millions of years to the origins of primates. However, by eight thousand to five thousand years ago, this nomadic lifestyle of tracking down the food sources needed for survival changed momentously during the Neolithic into a lifestyle in which small groups of villagers farmed resources. The invention and evolution of agriculture occurred rapidly compared with the long static period of hunting and gathering practiced by the immediate and deeply remote ancestors of
Homo sapiens
. Then, in just a few thousand years, farming villages expanded and became more socially and politically complex, with larger and larger populations, leading to temple towns, city-states, and eventually national states.
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By five thousand to three thousand years ago, state societies had appeared with a specialized institution of government. Having evolved from small groups of hunters and gatherers with relatively simple social organizations, state societies became richly diverse and complex, with individual members differing widely in wealth, status, and political power to influence others. Consider ancient Egypt, for example. The pharaoh governed all and commandeered the resources of the professional classes, such as engineers and accountants, as well as the physical labor of slaves to erect his own burial tomb for the afterlife. The shift from hunter-gatherers to the complex society of Egypt took, of course, multiple generations. Yet all this happened in the blink of an eye when framed against the time scale of millions of years of biological evolution and the deep time of geology.

The invention of pottery illustrates that innovation began to pick up steam during the Upper Paleolithic.
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Firing ceramic containers is a sophisticated step ahead of baking small clay objects and figurines in terms of its technical demands. The invention of pottery also implied an interest in cooking and preparing and storing food. Archeologists traditionally posited that first came the invention of farming and permanent settlements—an advance over the
hunting-gatherer culture that endured for tens of thousands of years—followed by the invention of pottery. It was believed that agriculture and pottery were thus innovations of the Neolithic period and were certainly no older than eight thousand years. The recent discovery of shards of pottery from the Xianrendong Cave in the Jiangxi Provence of China convincingly falsifies this assumption. Radiocarbon ages of the site indicate that pottery had been invented nineteen thousand to twenty thousand years ago in the Upper Paleolithic. The technology of pottery thus preceded agriculture. It was a much earlier innovation of hunter-gatherers to cook their food: “Pottery making introduces a fundamental shift in human dietary history, and Xianrendong demonstrates that hunter-gatherers in East Asia used pottery for some ten thousand years before they became sedentary or began cultivating plants.”
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Cultural change happens rapidly, as the relatively rapid ascent from hunter-gatherers to nation-states illustrates. The acceleration of cultural change in modern humans has continued to the point that within a couple generations the world can change so as to be almost unrecognizable. Consider the technological innovations of the past hundred years. In an editorial on consumption as an indicator of economic well-being, the
New York Times
published in its Sunday Opinion section (February 10, 2008) a chart plotting the percentage of US households with specific technologies from 1900 to 2005.
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For the argument advanced here, the chart (prepared by Nicholas Felton and titled “Consumption Spreads Faster Today) documents how quickly technological innovations penetrate our culture in recent years compared with a century ago. The telephone and electricity were scarcely used in 1900 and the automobile was as yet unknown. Radio and refrigerators were unknown until 1920. Air conditioning, clothes dryers, and dishwashers did not emerge until nearly 1950. Yet all of these technologies are taken for granted by Baby Boomers born after World War II. The acceleration of cultural change in the first half of the twentieth century altered the technological world of a Baby Boomer's parents and grandparents profoundly. As stunning, if not more so, is the explosion of technology during in the second half of the twentieth century. Among the technologies taken for granted by the Boomers’ children are microwave ovens, personal computers, cell phones, smart phones, and the Internet. It took less than twenty years for microwave ovens to penetrate into
80 percent of all US households. Telephones and automobiles required sixty years to do the same! It took more than forty-five years before 90 percent of households had electricity. From 1990 to 2005, cell phone use jumped from less than 5 percent of households to 90 percent, while personal computers did much the same by entering more than 70 percent of all households from less than 20 percent in the same fifteen-year interval. Only radio and refrigerators from the first half of the twentieth century showed adoption rates even close to those of the technological innovations of its last quarter.

Human beings alone manufactured advanced stone tools and symbolic art, invented and propagated language, and organized small villages and eventually large nation-states. These astounding cultural advances have taken place in a geological blink of the eye since the origin of the modern human mind a few tens of thousands of years ago. As Michael Tomasello has argued, biological evolution could not possibly explain the cultural world of modern humans. Our genetic similarity to other great apes is “the same degree of relatedness as that of other sister genera such as lions and tigers, horses and zebras, and rats and mice…. There simply has not been enough time for normal processes of biological evolution involving generic variation and natural selection to have created, one by one, each of the cognitive skills necessary for modern humans to invent and maintain complex tool-use industries and technologies, complex forms of symbolic communication and representation, and complex social organizations and institutions.”
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The radically different process of change underlying the human story is called cultural evolution. It alone can account for the acceleration of change that has characterized the history of our species. Cultural innovations added in one generation are carried forward into the future and are generally not forgotten and lost. Rather, they are learned by the next generation, either through imitation or by direct instruction. This allows innovations to accumulate from one generation to the next. The accumulation of past cultural accomplishments explains why the pace of change accelerates through time. As the cumulative total of innovations grows larger and larger, there are more and more places in which to innovate further. Thus, one would expect an acceleration of change from prehistory to modernity. Now, in the twenty-first century, after tens of thousands of years of cultural innovation, one should not
be surprised to see dramatic changes over the course of as little as one hundred years.