Crash! Bang! Wallop! Just when you think that Nature is on top, with an unbreakable headlock on Nurture, Nurture breaks free and starts pummeling Nature. The Nature-Nurture combat continues, a struggle raging since at least the time of Plato and Aristotle. More recently, the evolutionary psychologists have been wooing the press with their beguiling stories of the Darwinian origins of every behavior under the sun, and the geneticists have been singing the same seductive song with their genes for violence, anxiety, and personality. Nurture, it appeared, was down for the count.
Now Stephen Quartz and Terrence Sejnowski take the side of battered Nurture —culture, if you will—and ﬁght the good ﬁght against Nature, or genetic determinism. In their quest to slay the beast of genetic determinism and proclaim the victory of cultural biology, Quartz and Sejnowski range over vast and sometimes strange territory: the origin of high school killers; the inﬂuence of TV on social capital such as education; Dr Spock’s empathic skills; Mother Teresa’s immorality; Woody Allen’s personality; the neurochemistry of sex; why no society should have more than 150 members; the nature of intelligence; the meaning of happiness; the origin of personality; the sex life of bonobos; and why the Twin Towers were brought down.
Terry Sejnowski is “the world’s foremost theoretical brain scientist” (according to the book’s dust jacket), a professor of biology, physics, and neuroscience; director of the Institute of Neural Computation at the University of California, San Diego; and director of the Computational Neurobiology Laboratory at the Salk Institute in La Jolla. His work on neural networks— artiﬁcial systems capable of learning to read words—helped spark the neural-networks revolution of the 1980s, and since then Sejnowski has been pioneering the use of computers to model neuronal and brain behavior. He models single synapses, individual neurons, networks of neurons, and vast assemblies of neurons in an effort to understand the complex behavior that emerges from the interaction of relatively simple components. Stephen Quartz worked with Sejnowski at the Salk Institute and is now an associate professor and director of the Social Cognitive Neuroscience Laboratory at the California Institute of Technology in Pasadena. He recently received a million-dollar grant from the Packard Foundation to explore the neurobiology of moral and economic decision making.
The authors bill themselves as theoreticians, practitioners of the venerable trade that designs theories to catch the facts of the world. They wish to create a new scientiﬁc ﬁeld of “cultural biology,” which would study how our culture—our environment as social humans—affects our neurobiology and how our neurobiology affects our culture.
As an illustration of how culture affects neurobiology, Sejnowski recently found that exercise stimulates the birth of new neurons and new connections in an area of the brain central to memory (the hippocampus), thereby improving memory formation. As an example of how neurobiology affects culture, Quartz is using brain imaging to investigate how the structure of our visual cortex determines our visual aesthetic, which in turn will determine what kinds of things we surround ourselves with, and in what we ﬁnd aesthetic pleasure.
The authors are offended by genetic determinism. They view as demeaning the explanation that our psychology is based on “selﬁsh” genes. Still, they are far from being environmental determinists, as are the empiricists or behaviorists who maintain that the mind at birth is a blank slate to be written upon by experience. Rather, they believe that it is the interaction between genetics and culture that shapes the individual self.
HOW TO GROW BIGGER BRAINS FAST
Culture changes the structure of our brains in myriad ways. Every time we open our eyes or attune our ears, the electrical and chemical activities of billions of neurons and their connections are almost instantly changed. Every electrical and chemical change, if sustained, leads to a change in gene expression, and eventually a change in neuronal shape and connection. This is called plasticity. The building of our brains during development and beyond is done in concert with culture. If something is missing from a child’s culture—light, sound, novelty, maternal love—then corresponding parts of the brain shrivel up or do not develop fully. On the other hand, if the culture is ﬁlled with many novel experiences, then corresponding parts of the brain may expand or even change function. For example, brain imaging of blind people reading (touching) braille showed that their visual cortex was transformed into a touch-processing area.
Quartz and Sejnowski suggest that development and learning, traditionally considered separate processes, are in fact part of the same process called “constructive learning.” If we learn over several months to play the piano, the structure of our brain changes. The area of the motor cortex controlling our ﬁngers enlarges and is reconﬁgured such that complex patterns of movement that initially required our intense concentration become unconscious programs. A similar change may take place in the auditory cortex as the experience of music reshapes our neuronal connections, allowing us to perceive patterns in the sound that we could not perceive before. Humans share almost identical genes, but, the authors conclude, the cultural/environmental diversity of our childhoods and later years creates a diversity of brains and selves.
This human variation is striking compared to the relative uniformity of, for example, chimpanzees—yet humans and chimpanzees share 98.4 percent of their genes. How does this minuscule difference in genes result in such a huge difference in way of life? The authors argue that human brains evolved to be receptacles of culture; furthermore, this culture drove our evolution. One of the pivotal biological differences between humans and our nearest relatives— chimpanzees and bonobos—is that our brains are three times larger.
The authors speculate that this difference in size could easily have been brought about if we evolved to reach older and older ages before our neurons stopped proliferating, leading to larger brain size and extended brain development. Recent research indicates that the human brain continues to grow and develop throughout childhood and adolescence, particularly in areas such as the prefrontal cortex that are involved in higher-order processing and the sense of self. In fact, humans require a remarkably long time to develop into adults. From the point of view of survival and reproduction, this is wasted time, but Quartz and Sejnowski see the long developmental period of the nervous system as an increased opportunity for culture to produce an adaptable brain.
Furthermore, the last million years or so has been a period of extremely varied climate, with the repeated advance and retreat of ice sheets accompanied by large and rapid changes in temperature and rainfall. Environmental variability could have favored the evolution of humans able to adapt to the prevailing conditions. One way to do that would have been to evolve culture, the transmission of knowledge and behavior by language or mimicry. Thus, the cerebral cortex spread out on the top of the brain to receive the culture, and the culture spread from brain to brain, maximizing the ability to survive. The existence of cultures inﬂuenced evolution, creating a feedback loop that may have accelerated the evolution of brain and culture in tandem.
By delaying the age at which neurons stop increasing, humans could grow bigger brains over a longer period, with ample time for cultural conditioning. As receptacles of culture, human brains became both adaptable and diverse, and the emergence of culture inﬂuenced our genes to produce brains that were even more receptive to culture. In short, we bootstrapped ourselves to bigger brains.
THE CHEMISTRY OF SELF
Having sorted out human origins, Quartz and Sejnowski go in search of the origins of self within the brain. They discover a dichotomous self consisting of an “internal guidance system,” embedded in our ancient neuromodulatory apparatus, and a “user’s guide to life,” located in the outermost (and most recent) parts of the brain, speciﬁcally the prefrontal cortex. The internal guidance system consists mainly of the brain’s arrangements for motivation, addiction, and reward—the dopaminergic neurons of the ventral tegemental area (VTA) of the basal ganglia. Stimuli ranging from a hug or candy to gambling and sex have motivational value, triggering surges of dopamine. Those surges feel good, while the absence of dopamine feels bad. Back in the 1960s, rats with stimulating electrodes inserted into this dopamine system were found to self-stimulate themselves continuously, ignoring even food and sex.
Quartz and Sejnowski do not believe, however, that the VTA is solely a pleasure center. Their view is that, based on past experience, VTA cells predict a reward from an anticipated action, then compare the actual outcome to the prediction. If the outcome is better than predicted, a big surge of dopamine is produced, and if it is less than predicted, dopamine activity drops. This was shown in the dopamine neurons of monkeys when they were taught to associate a light signal with the subsequent presentation of a slice of apple. Initially, the neurons ﬁred when the apple was presented, but once the monkeys learned the association, the neurons ﬁred when the light signaled. If the apple was not presented after the light signal, though, the neuron response decreased dramatically.
Thus the dopamine neurons appeared to be measuring the divergence between the prediction of a reward and the actual outcome. This measurement of divergence can then be used to make better predictions, and forms the basis of a powerful form of learning in which the system optimizes its function based on predictions of outcome or reward. The same form of learning has been incorporated into computer programs to help them learn from their mistakes. For example, this is how the TD-Gammon program became a world master at backgammon. Sejnowski has made a computer model of VTA neurons based on these principles and believes that the neurons learn to predict future reward based on past experience. This is the basis of the internal guidance system, which is trying to predict and maximize certain rewards—originally programmed by our genes—such as the pleasure associated with sex and food.
The ancient internal guidance system in the VTA is connected to the modern “user’s guide to life” in the prefrontal cortex. It is mainly in the prefrontal cortex, according to Quartz and Sejnowski, that culture is represented in the brain: beliefs, values, and reasoning. Through connections to the VTA, which in turn is connected to and can release dopamine in the brain (including into the prefrontal cortex), cultural beliefs can affect motivation and emotion can color reasoning. Self-concepts and cultural identities are lodged in the prefrontal cortex, and this area adjusts behavior to match the speciﬁc context or environment. Damage to the prefrontal cortex results in socially inappropriate behavior and emotion; this may be what is going on in people we label sociopaths.
The authors believe that the self is created in the interaction between the prefrontal cortex and the VTA. This concept of self harks back to that of Plato, who likened the mind to a chariot drawn by two horses, intellect and emotion—together an unruly pair. The authors believe that intellect and emotion are intimately linked, making it possible to be addicted not only to love but also to beliefs and ideologies that evoke strong emotions.
MUTANT MONOGAMOUS MICE
Quartz and Sejnowski turn next to the origin of society, another piece of the puzzle of how culture affects the brain and development of the self. Why do we humans live in society? Is it, as Thomas Hobbes suggested, that society originally consisted of warring individuals who gave up their independence to a supervisory state or leader in exchange for protection against murder, rape, and pillage by their fellows? Or is it, as Aristotle suggested, that humans have a social instinct or need, like the mother-baby bond, that glues us together?
The authors gamely set out to identify the biological basis of such an instinct somewhere in the depths of the brain. They invoke research suggesting that parent-child bonds, the bonds of romantic love, and the bonds of friendship may all have a common root in the brain. All, for example, activate brain systems using the chemicals oxytocin and arginine vasopressin (AVP); endogenous opioids such as the endorphins, which mimic the actions of heroin inside the brain; and dopamine. These chemicals surge in the brain during breast-feeding, sex, and the friendly touching involved in social grooming; since we want more of the feelings they produce, we are motivated to maintain our social and cultural bonds.
They mention the strange case of the mutant monogamous mouse. Mice are usually polygamous; but there is a species of related rodent, the vole, that is monogamous, displaying afﬁliative behavior with one partner only. In general, injection of AVP into the brain increases this afﬁliative behavior in voles, but does not have a similar effect in mice. Transgenic mice that were created to have the vole’s AVP receptor did, however, increase monogamous afﬁliative behavior when injected with AVP.
Human evolution may have hijacked these neurochemical systems to create a social bond, so that we are, in effect, addicted to society and culture. To yield a truly social human, however, Quartz and Sejnowski believe that this social urge had to be complemented by the development of both social identities and a theory of mind.
VISIONARY SCIENCE GRAPPLING WITH REALITY
At times one cannot help thinking of Quartz and Sejnowski as being on a quest to conquer all known problems in the universe using a conceptual system—cultural biology—that is only partially visible to the bemused reader. Are they visionaries or deluded fools? Are they theoreticians who have cut loose from reality into a parallel universe of their own imagining? For many important problems they propose plausible explanations, but there may be thousands of plausible explanations for problems such as the origins of violence, intelligence, self, or society. In science, proposing a plausible theory of how things are is the easy part; grappling with reality in order to prove it is where the difﬁculty lies.
The authors are implicitly asking us to trust them because their soft explanations are supposedly based on hard science. The subtitle of the book is What the New Brain Science Reveals About How We Become Who We Are, but their new insight often turns out to be simply that one neurochemical or brain structure may be involved, which does not really help us understand the social or psychological issue. The authors rightly condemn simplistic notions of there being a gene for violence, personality, or self, but then they defend a brain structure or a neurochemical for the same immensely complex phenomena.
To its credit, the book is miraculously accessible. Its style is conversational and magazine-like in its use of stories, anecdotes, people, and analogies. You will learn a lot by reading it, and have a lot of fun along the way. But given the authors’ backgrounds in explaining complex behavior using computer systems, I expected more insight into how complex behavior emerges from interaction among simpler units. They succeed when talking about reward-based learning, using research on the neural circuits of bees and then computer models. But when they move on to more complex behaviors in humans, where relatively little of the neuroscience is known, their explanations tend to ﬂoat free of the underlying science. The speculative reasoning that follows is not science, but is it in some legitimate sense popular science? Perhaps we could call it “visionary science,” pushing back the boundaries of what can be imagined at the interface between biological science and social science.
Quartz and Sejnowski would unchain us from genetic determinism and provide us with a more empowering vision of ourselves, but all they offer us in exchange are the bonds of cultural determinism. Why should we ﬂee our selﬁsh genes only to become enmeshed in a web of cultural constructivism?
CREATIONS OF OUR OWN SELVES
In the end, I fear, the authors’ vision of the self lacks a beating heart. It lacks even a semblance of free will, a free agent to ponder, decide, and act. They do discuss the narrative self, the image of ourselves in the past and future that we and society construct to hold our memories, hopes, and fears, but they shy away from dealing with the self-conscious self of the present: the stream-of-consciousness self that is apparently pondering, deciding, and acting as a free agent. They excuse themselves from dealing with this embarrassing feature of mind by saying that to do so would require solving the infamous mind-body problem and that, besides, consciousness is an overrated feature of the mind. This is a poor excuse. Recognizing a module of mind that is apparently pondering on experience and deciding on action does not necessitate solving the mind-body problem or even abandoning determinism.
Indeed, many psychologists have given deterministic accounts of a self-monitoring and attention-directing module within our brain. If you close your eyes and plug your ears, you will experience a continuous internal monologue, a stream of hopes, fears, and fantasies, as well as half-constructed images and half-digested memories. This monologue provides a narrative commentary on all your experience, like an excitable sports commentator narrating a football game. But this internal monologue also ponders choices and makes decisions—the conscious thought process. No vision of self is acceptable or empowering without an account of the conscious self and its apparent ability to act within the mind. If a future ﬁeld of cultural biology aims to discover how culture determines human behavior, it needs to provide an account of how culture affects the internal monologue and the stories we tell ourselves. We are not determined only by our genes and our culture. We are also creations of our own selves.
Quartz and Sejnowski imagine this new world of cultural biology for us, and by persuading us to see that world through their eyes they hope to bring it into existence. As with Don Quixote and Sancho Panza, even while laughing at their naiveté, we feel a sneaking respect for their bravery and intensity of vision, and perhaps a niggling worry that we simply lack the vision to share their fantastical world.
From Liars, Lovers, and Heroes: What the New Brain Science Reveals About How We Become Who We Are, by Stephen R. Quartz and Terrence J. Sejnowski. © 2002 by Stephen R. Quartz and Terrence J. Sejnowski. Reprinted with permission of William Morrow and Co.
EMOTION’S ANCIENT ROOTS What is so surprising about this tangled web is that its roots are in ancient brain structures whose basic functions can be found in animals as diverse as bees and humans. We took the fact that these structures are so highly conserved across species to suggest that they must hold some essential truth about how brains work. For example, one structure, called the ventral tegmental area (VTA), is buried in the deep recesses of your brain in a region called the basal ganglia, which lies beneath the cerebral cortex, and is part of a powerful reward system; indeed, this is the system that drugs of addiction hijack. We postulated that perhaps emotions, motivation, and reward are all facets of a single, powerful way to design brains.
Computer models of the VTA in Terry’s lab were revealing that this brain area could learn to predict future reward based on past experience. For example, if you perform well at work, you might expect a bonus at Christmas, as happened last Christmas. We realized that the VTA and related structures are your internal compass. It fills your world with values, provides emotional tone to your experiences, and helps you decide what fork in the road to take when you face decisions. It is your internal guidance system, creating desires, propelling you to action, and helping you get on in the world by predicting the benefits of possible decisions. It is why you are not just an inert piece of clay to be molded by the world, or a collection of genetic reflexes optimizing fitness.
The intrigue deepened when we discovered that the VTA sends its fibers to the prefrontal cortex, which is a key to your humanity, mental flexibility, and sense of self. How and why was an ancient structure, the VTA, intertwined with the prefrontal cortex? An important clue came from development. Damage to the VTA impairs the development of the prefrontal cortex and leads to severe mental retardation. We realized that this ancient structure is at the core of a tangled web that bootstraps us into culture and helps construct the human mind.
The VTA first sparks to life in the child. It is the vital force that propels you to actively engage the world with the human texture that a Spock could never know. Evolution shaped your brain not by departing from the powerful reward-based systems that you share with the bees, but by adding new layers onto this basic architecture and extending its development. Even in adulthood, these two intertwined brain systems operate in close concert. Together, they underpin your everyday thinking, planning, and decision making. Indeed, their joint workings suggest that the age-old dichotomy between thought and feeling, intellect and passion, is a faulty one, carrying important implications for your inner life.
This, then, is the basic view of the mind that cultural biology reveals, a sort of Upstairs, Downstairs in which old and new come together to create your immensely complex behavior. The human dramas that we will encounter in later chapters have their roots in the interplay between the VTA, other subcortical structures that utilize the chemical messenger serotonin, and the prefrontal cortex, and in the tension between old and new components of this normally integrated behavioral system. It is at once ancient and new, a far more powerful way to generate flexible behavior than genetic reflexes and far stranger and more fascinating than Plato or psychoanalysts ever imagined.