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Why the Topic of Bioethics in Science Classes?

A New Look at an Old Debate

by Carolyn Csongradi

"Nurture" Is In Equilibrium With "Nature" During Critical Periods Of Vulnerability:

During critical windows of exposure, experiences chemically and anatomically modify the brain structures over a lifetime. We have inherited important capabilities and tendencies, but these require shaping.

Physiological evidence:

The mammalian visual system has been studied extensively for more than forty years. In 1981, neuroscientists David Hubbel and Torsten Wiesel received a Nobel prize for their work on the developing visual cortex .(20) They performed experiments recording the activities of individual brain neurons after selectively depriving newborn animals of different types of visual stimulation. Early experiences (or lack thereof) have a direct influence on how the animal perceives the world as an adult and structural differences were observed in the brains of these animals. Scientist Francis Crick reflects the philosophy of Reductionism when he said, "The scientific belief is that our minds - the behavior of our brains - can be explained by the interactions of nerve cells (and other cells) and the molecules associated with them".(8) This "reductionist" approach, which means a complex system can be explained by understanding the behavior and interactions of the components, has been a driving force in scientific development.

The evidence supporting the hypothesis that environmental experiences influence shape anatomical brain structures is powerful has been substantiated by neurophysiological experiments. For example, recent studies done on spinal cord paralysis and the role of a molecule called GAP-43, which turns on for cell growth and repair, suggests that the nervous system has critical periods of plasticity from a biochemical point of view as well as a structural one. This finding elegantly supports the behavioral observations of Piaget while offering an explanation for why children may recover from serious brain injuries where adults would have a very poor prognosis.

Additional support is found in a second relevant article, " Male Call " reprinted from a book by Robert Sapolsky.(38) Sapolsky studied the relationship between aggression and testosterone levels in males. What he observed was that in castrated animals, changing the levels of testosterone over a wide range produced little differences between pre-surgical aggression and that seen with differing amounts of chemical replacement. He concluded that a minimum amount of testosterone was required to allow for aggressive behavior - "give permission" was his term. Social conditioning seems to more than make up for much of the lower hormone levels. The picture appears to be a complex interaction between environment, previous social experience and chemistry.

In his recent book, Nobel laureate neurobiologist Gerald Edelman developed a hypothesis supported by extensive neuroanatomical and physiological studies. He argued that repeated common experiences strengthen key neuronal connections through frequent firings.(10) The result is to develop and reinforce anatomically based concept maps which are formed from groups of neurons linked by common experiences, not unlike the categories proposed by Kant. These concept maps subsequently modify how sensory information is processed and organized.

Behavioral observations:

A recent article, " Name That Tone ", was written by two geneticists who studied perfect pitch and its relationship to musical training.(15) Some people have the ability to recognize or play a specific musical note without hearing a reference note. This is called "perfect pitch". To cast some light on whether "perfect pitch" was inherited and/or learned, a study was conducted in which 620 music students were surveyed for their ability to recognize a particular musical note. Those who received musical training before the age of two had the highest percentage of individuals with "perfect pitch" (about 7%), while only 2% had "perfect pitch" when given musical training after age twelve. Both nature and a critically timed nurturing were responsible.

A more familiar example is the medical condition known as " lazy eye". If the brain fails to receive input from both eyes in the early years of life, the information from the eye with very poor vision is permanently discounted even after corrective surgery or lenses. Yet, a baby swaddled for most of its first year of life will still walk normally during the second year. Plasticity seems at a maximum during the earlier years of human life, but there is evidence of residual plasticity in adults who recover from the devastating effects of strokes. (11)

In species other than mammals, a similar pattern of critically timed vulnerability for the nervous system also exists. The acquisition of bird songs has been extensively studied in the context of what is inherited and if critical windows of exposure exist for normal song to develop. Some birds such as doves, who have a species specific cooing rhythm, are unaffected by efforts to disrupt their learning. Their song must have a genetic model which does not require environmental "priming". The sparrow, however, needs to acquire a "model" or template for the species specific song sometime during its first four months of life or it fails to produce a normal song even with subsequent adult song exposure.(19)

One last thought provoking comment by an evolutionist, Ernest Mayr, "Man is distinguished from all other animals by the openness of its behavioral program... so in human beings ethical norms and definite values are laid down in the open behavior program of an infant."(29) He further states this is a very special type of learning akin to imprinting based on an innate capacity to acquire the ethical beliefs. There is disagreement during what period humans most easily acquire these values. Daniel Keating, a cognitive scientist, believes adolescence is the period when individuals discover a role for feelings and aspirations which make sense in terms of the overall community needs and expectations.(24) His work is strongly supported by the observations of educational psychologist Carol Gilligan, who concludes after a longitudinal study of young girls that adolescence is a period during which self in relationship to others becomes critically important.(13)

Nature and Nurture Continued:

In Summary...

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