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The Almost Blank Slate Making a Case for Human Nurture

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The Almost Blank Slate Making a Case for Human Nurture 34 The Almost Blank Slate Making A Case For Human Nurture HENRY D. SCHLINGER IN 2002, THE PSYCHOLOGIST STEVEN PINKER A Case for Human Nurture appeared on the New York Times bestseller list In his review of Pinker’s book, the behavioral with The Blank Slate: The Modern Denial of biologist Patrick Bateson wrote that it may lead Human Nature,1 a book that attempts to catapult to “yet another round of the tedious and increas- the nature-nurture issue back into public debate, ingly irrelevant nature/nurture debate.” 2 while squarely coming down on the side of Although I resist being drawn into more tedious human nature. I shall argue, however, that there debate on the nature-nurture issue, Pinker’s is overwhelming evidence that learning exerts prominence as a public intellectual demands a the most significant influence on human behav- rejoinder and compels me to make the following ior—a fact that is rarely acknowledged, publi- assertions: cized or even understood. If anything, there is a • Humans come into the world much closer modern denial of human nurture, not human to the blank slate end of the continuum than any nature. other species. VOLUME 11 NUMBER 2 2004 THE ALMOST BLANK SLATE 35 • Most of what humans know or know how The crux of the debate is not whether genes to do is not present in any form at birth. influence learning or behavior—no behavioral • Many, if not most, of the important similari- scientist would claim they don’t—but rather how ties and differences in behavior between individ- they influence learning and behavior.5 The flip uals can parsimoniously be explained due to side of the question, and the one of interest to learning. me as a behavioral psychologist, is how the These are so obviously true it seems odd to experiences we call learning influence behavior. have to repeat them, but the scientific evidence This question is much easier to answer because for the influence of learning on human behavior the experiences that produce learning are easily is overwhelming. accessible to experimental scrutiny and there All other species rely more upon reflexes or already exist decades of sound experimental fixed-action patterns that, although not insensitive work from which to draw. But first we must clar- to learning experiences, are relatively stable. ify the relationship between learning and evolu- Examples include aggressive displays, courtship tion by natural selection as causes of behavior. and mating, migration, imprinting, and care of young. Human behavior, on the other hand, is Ultimate Causation of Behavior noteworthy for its variability. As the evolutionary The nature-nurture debate is typically portrayed biologist Douglas Futuyma so aptly put it: “On as a simplistic paradigm where, in the nature cor- balance, the evidence for the modifiability of ner, proponents claim that genes exert the over- human behavior is so great that genetic con- riding influence on human behavior, such as lan- straints on our behavior hardly seem to exist. guage, intelligence, and social and sexual rela- The dominant factor in recent human evolution tions. In the nurture corner, proponents argue has been the evolution of behavioral flexibility, that learning exerts the overwhelming influence. the ability to learn and transmit culture.” 3 Put in these terms the nurture proponents win The renowned evolutionary biologist, Ernst hands down. In other words, even though our Mayr, has also acknowledged the flexibility of ability to learn is made possible by a nervous human behavior with his distinction between system shaped by a particular evolutionary histo- open and closed programs. According to Mayr, ry, the experiences scientists call learning “closed programs” include reflexes and account for most of the similarities and differ- fixed-action patterns controlled by areas of the ences between individuals. In this regard, as brain that are rigidly programmed by genes. behavioral psychologist Galen Alessi suggests, Other areas of the brain (e.g., the language learning may be viewed, along with evolution, as areas) are suitable for “open programs” because a set of ultimate causations of behavior.6 the information is not rigidly programmed the Since at least the early 1960s, Ernst Mayr has way that reflexes are. These areas are primed by argued that every process in living organisms is certain learning experiences early in life while the result of two separate causations called proxi- even more general areas of the brain (e.g., the mate (i.e., functional) and ultimate (i.e., evolu- association cortices) remain malleable to learning tionary). Ultimate causation explains why an experiences throughout life.4 organism is the way it is, as a product of evolu- No one would deny that genes, selected tion. According to Mayr, because ultimate causa- throughout human evolutionary history, code for tion relates to the origin of adaptation or diversity, a nervous system that makes possible our it answers “Why?” questions, such as “Why are extraordinary ability to learn, or that some genes desert animals usually colored like the substrate?” may be specialized for such learning. But let us Such questions “deal with the historical and evo- not forget that all genetic expression, from rela- lutionary factors that account for all aspects of tively simple Mendelian traits such as eye color, living organisms that exist now or have existed to complex behavioral tendencies such as verbal in the past.” Mayr reminds us that it was Darwin behavior, is dependent on environmental input. who was responsible for making “Why?” ques- Such input can be located on a continuum from tions scientifically legitimate and for bringing “all the very simple stimuli that elicit reflexes to the of natural history into science.”7 complex associative processes that produce If we want to know why an organism learning. exhibits a particular behavior, we are asking WWW.SKEPTIC.COM 36 Nature or Nurture? about the behavior’s natural history and its ulti- point, however, locating areas of the brain relat- mate causation. Therefore, it makes sense to ed to certain behaviors in no way implicates adopt Alessi’s modification of Mayr’s strictly evo- inheritance as an ultimate cause. For example, a lutionary (or phylogenetic) account of ultimate recent study compared brain scans during recog- causation to include the life history (or ontogeny) nition tests in adults, who as children were of the organism. Thus, in this neo-Mayrian view, judged as shy or inhibited, with adults who were the ultimate causes of behavior, especially in not judged as shy.13 The results showed more humans, occur in both the evolutionary history activity in a certain area (the amygdala) of the of the species and in the learning history of the brains of the once-shy adults. The media report- individual. Explanations involving both types of ed that the study lent support for the inheritance ultimate causations necessarily involve specula- of shyness. However, nothing in these, or any tive accounts of the natural history of the behav- other results purportedly showing brain-behavior ioral phenotype—interpretations based on basic relationships, suggests inheritance as the ultimate principles of evolution and learning and carried cause. Simply identifying structures in the brain out by evolutionary biologists and behavioral that seem to relate to behavior does not in and psychologists respectively. of itself implicate either evolution or learning as the ultimate cause. Evolution, Learning and the Nervous System In fact, a sizeable body of research shows Naturists try to buttress their position by mar- that learning changes the physical and chemical shalling evidence from neurobiology. They do structure of the brain. Readers may already be this in at least two ways. First, evolutionary psy- familiar with experiments by Mark Rosenzweig, chologists assert that there are specifically William T. Greenough, and their colleagues evolved modules in the brain that underlie partic- which show that placing rats in either impover- ular human abilities.8 Other scientists seriously ished or enriched environments produced question such claims, however. For example, changes not only in their behavior but also in the neuroevolutionary psychobiologists Jaak and structure of neurons and synapses in their brains Jules Panksepp bluntly state, “By simply accept- (e.g., dendritic branching, synaptic and neuronal ing the remarkable degree of neocortical plastici- density, and synapses per neuron).14,15,16 Other ty within the human brain, especially during research on non-human animals shows that spe- development, genetically dictated, sociobiological cific learning experiences produce measurable ‘modules’ begin to resemble products of dubious changes in the nervous system. For example, the human ambition rather than of sound scientific Nobel prize-winning neuroscientist Eric Kandel reasoning.”9 Psychologist William Uttal calls this and his associates have shown changes in the modular approach “the new phrenology.”10 In structure and function of individual neurons as a fact, serious scholars argue that instead of con- function of classical (Pavlovian) conditioning.17 taining specifically evolved and specialized mod- And research by Joseph LeDoux and his col- ules (for emotion, language, etc.) as evolutionary leagues has shown that classically conditioned psychologists suggest, the human brain is more fear in rodents changes the amygdala, which accurately described as consisting of subcortical controls fear reactions by way of output projec-
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