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Smithin tutkimustyö on perustunut paljolti laboratoriokokeiden käyttöön taloustieteellisessä tutkimuksessa. Nykyisin Smith toimii taloustieteen professorina George Mason Universityssä ja tutkijana yliopiston poikkitieteellisessä taloustutkimuksen laitoksessa.
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Many children who grow up in poverty have higher levels of behavioral problems and lower IQ scores than children who grow up in middle class families. However, some children from poor family backgrounds are resilient -- that is, they behave better and score higher on intelligence tests than might be expected given the level of social and economic deprivation they have experienced.
Researchers have identified several protective factors that promote children’s resilience, including a child’s easy, sociable personality, a mother’s warmth toward her child, and a stimulating home environment. However, we still don’t know to what extent these protective factors and children’s resilience might be associated with a common genetic factor.
It may be that the genes involved in promoting the protective factor are the same genes that promote child’s positive development under conditions of poverty. For instance, the genes that contribute to a mother’s emotional warmth could be the same genes she passes onto her child, which promote the child’s resilience. In this study, we tried to determine the degree to which genetic versus social-environmental influences explain children’s resilience against poverty.
Children’s behavioral and cognitive resilience to poverty was influenced by their genetic makeup. This suggests that children themselves are agents in rising above their experience of poverty. For example, we found that children with a genetic disposition to be friendly, sociable, and outgoing had the most resilience against poverty.
Importantly, however, children’s resilience was also affected by their rearing environment. After controlling for genetic effects, we found that mothers who engaged in more stimulating activities with their twins helped promote their children’s resilience against poverty. This finding suggests that encouraging parents to engage in activities with their children (e.g., a long walk or a museum visit) can help protect children’s intellectual development from the damaging effects of socioeconomic deprivation.
Thus, both genetic and social-environmental sources of protection are involved in helping children overcome the hardship of growing up poor.
Child Development, Vol. 75, Issue 3, Genetic and Environmental Processes in Young Children’s Resilience and Vulnerability to Socioeconomic Deprivation by J. Kim-Cohen, T. E. Moffitt, A. Caspi, and A. Taylor.
"Nurture" Is More Influential Than "Nature"
Experiences are written onto the mind, which is essentially a blank slate. We have knowledge of the world because we learn from experiences. "Prior to experience, the human mind is a 'white paper', void of all characters, without any ideas. " Each aspect of behavior is acquired from the environment.(23)
Philosophical discussion
The philosopher Hume thought the mind a blank slate(tabula rasa) on which experience could be written. Hume was preceded by another philosopher, John Locke who was also a contemporary of Isaac Newton. They belonged to a school of thought known as Empiricism which states that knowledge is derived from experiment and observation and were joined by science contemporaries, Sir Francis Bacon and Robert Boyle.(16) Locke thought all knowledge of the world was gathered through sensory experience. This information coul d be manipulated into more complex ideas by reflection and reasoning. He saw the mind as having innate powers of observation, but not of ideas which were to be constructed from sensory input. Hume, expressing the extreme of skepticism, felt nothing was objective, everything was chaotic, connections between impressions were imagined.
Critics observed that this line of thinking could not explain cause and effect in a novel situation unless one was allowed to rely on a multitude of previous experiences. Berkeley, a contemporary of Locke, argued that Locke's logic led to the conclusion that all knowledge ultimately becomes ideas in the mind which may or may not resemble reality. Our perception of nature is a mental experience. Kant, who was familiar with the discoveries of Newton, helped solve this conflict. He argued that while knowledge came from sensory information, we have inherited the ability to categorize sensory information with respect to time, space and causality. A rock thrown at a window will break the glass. The future should look like the past.
The "Natural Law Theory" argued that moral principles could be discovered through careful reflection.(31) Reasoning was needed to counter or balance the natural inclinations of individuals. These laws of nature, rather than the individual customs and preferences, determined what action was "right". While the powers of reason were a part of the mind, principles were not. They remained to be found by observing nature.
Essentially, this is a philosophical discussion about how sensory knowledge is organized by the mind. Do we have an innate ability to manipulate objective sensory information or must this be learned entirely from experience? This difference in opinion is not likely to lead to any resolution of questions concerning the origin of values or moral knowledge nor explain the large body of scientific literature eq uating structural changes in biologic systems with learning.
Neurological studies
In a recent best seller, neurologist Oliver Sacks examined a man, Virgil, who had had cataracts clouding both eyes following an early childhood illness.(37) Earlier, several physicians had examined Virgil's eyes and concluded his retinas had been damaged as well by the same illness and concluded cataract removal would be futile. As an adult Virgil was functionally blind. At age fifty, Virgil was once again examined by a specialist whose opinion differed from earlier recomnnendations. This physician felt Virgil's retinas might have limited function and recommended removing both cataracts. Virgil agreed and thus became a fascinating opportunity for Sacks to study perception and the role of nature in visual learning.
After the surgery, Virgil reported seeing blurred visual images and had little ability to identify what he was seeing. For instance, a face seen wasn't known as a face until touched and he was unable to make sense of facial expressions. His primary route for knowledge of objects continued to be tactile. Over time, he showed little sense of depth perception, having difficulty judging objects in the distance from those which were close. He was as Sacks said, mentally blind.
After struggling for many months to learn to navigate visually, Virgil began to have long periods of spontaneous blurriness which were not observed by his doctor in patients who had had cataracts for a much shorter time. Sacks and the opthamologist concluded Virgil's visual cortex was in neural overload and responded by a sudden shutting down. This process of disconnection has been observed in many different animals when feeling overwhelmed.
In the end, his retinas continued to have the same physical appearance and Virgil's perception continued to deteriorate. Virgil became more blind than he had been befo re his operations, although he experienced rare moments when he could see something accurately. Whether this ultimate loss of vision was related to an intervening bout of a near lethal pneumonia or excess sensory stimulation could not be determined. What is clear is that nurture plays a major role in our ability to make sense of visual stimuli. Seeing is not necessarily "to see". Even if an alternative mode is developed for object identification, this coneptual information does not appear to transfer readily between sensory systems.
"Nature" And "Nurture" Interact In Sequential Stages:
Certain experiences are crucial to the maturing brain which develops in a series of stages such that the success of the next developmental stage depends upon the previous one. Our inherited nature is augmented by appropriately timed stimulation and the results can be tested behaviorally.
Behavioral observations
In the early 1900's, Piaget was the best known proponent of the hypothesis that children are born with few of the concepts possessed by an adolescent. His ideas were based on a series of elegantly designed experiments which studied how babies and young children acquired the concepts of object, space, and cause and effect. He proposed that children pass through a series of developmental stages where one stage builds upon the other by a process of assimilation followed by accommodation to the realities of the world. The process is largely one of brain maturation with appropriately timed environmental stimulation.
Piaget has been criticized for emphasizing a specific form of thinking which is more relevant to Western cultures. Subsequent experiments have demonstrated that individual stages are achieved in a less step-wise, more continuous fashion over a wider range of ages than he would have predicted. His theories do not always generalize across different content areas. For instance, the same child may show a grasp of the conservation of volume in one situation but not in another.
Another way to look at the interaction between the developing mind and environment has been to study the mother-infant bond. The mother is often considered the infant's first experience with an object from the world. During the 1930's Renee Spitz followed by John Bowlby studied infant deaths in foundling homes and in long term hospitalization. These sterile environments lacked visual and tactile stimulation and although they had adequate care in the strict sense, human contact was notably absent. A significant percentage of these babies died in the first year. In the early 1950's Harry Harlow experimented with social isolation in newborn monkeys which extended from birth to as long as one year. These monkeys were severely socially impaired as a result of the isolation. Such vulnerability was not detected when older animals were isolated.(17)
D.W. Winnicott, a 20th century British psychiatrist, coined the term " good enough mother", theorizing that there was never just an infant, but an infant-mother pair. Babies gain knowledge about objects from their experiences with the mother. If young children are deprived of a nurturing environment, such as in the case of an alcoholic or abusive parent, infants learn that objects come and go unpredictably. He believed this early exposure to the concept of object permanence (or impermanence) continued to influence how these children learned about other real world objects in a skewed way through out their lives.(43) A colleague, Arnold Modell, went one step further by stating the capacity to know and the capacity to love are not separate functions.(22)
While the pre-programmed information for grasping, sucking and orienting toward human faces are instinctual requirements for Piaget's developmental theories, they may become impaired through neglect and abuse by caregivers. Reality is constructed from what we know and what we value as important from experiences occurring at a very early age.
In the developmental model, natural selection has encouraged the brain to be flexible at certain key periods rather than emphasizing an assessment of the environment. The nature based model valued receptors for gathering environmental information. The genes selecting for brain plasticity were less important. While we might reasonably expect to find a gene or genes for instinctual behaviors, the full development of an individual would depend on being exposed to certain stimuli, to establish the basic building blocks for sequential development.
A generous interpretation of all these data is that humans might learn anything at any time given sufficient stimulation with rare exception. Exceptions, such as autistics who seem not to develop empathy for others, despite repeated exposure, are demonstrating a different neural learning program. Perhaps a more rationale conclusion is one which acknowledges that each species is primed to receive certain kinds of information which is most easily incorporated during critical windows of developmental opportunity. The nervous system likely has periods of greater flexibility with respect to learning in culturally sensitive periods. What also seems clear is that the loss of brain plasticity is neither linear with time nor completely predictable.
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