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Erica Reinig
Article Summaries
January 28, 2004
“Mirror of Reality”
People, especially philosophers, have pondered about perception and the nature of
reality for hundreds of years. Most philosophers would agree that every animal perceives
its reality differently. Recently, studies have been conducted on how perceptions are
different and why. Scientist Lettvin, while studying perception in frogs, discovered that a
frogs visual brain (its eyes and optic nerve) is predisposed to look for quick uneven
movements in its surroundings. Lettvin calls these “bug perceivers.” If a person were to
try to help a frog in a contained environment by killing all the bugs for the frog, the frog,
ironically enough would starve because it could not “see” the bugs. In a related
perception experiment, two groups of kittens were placed in two different environments:
one chamber with vertical strips and one chamber with horizontal stripes. When
released, the kittens raised in the vertical environment were unable to see any objects on
the horizontal plane (for example, a table top). The kittens raised in a horizontal
environment were unable to see any objects on the vertical plane (for example, a table
leg). The conclusion developed was that visual processing would program itself
according to the surrounding environment. According to this conclusion, the perception
and visual programming of a lab animal can be programmed during a critical period of
development. The large differences between perceptions in different animals can be
related to survival techniques. The animals “see” only what the brain is programmed to
“see,” bugs jumping for example. Studies have also shown that perceptions of reality can
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be difficult to change later in life. When a blind man, S.B., was given back his sight after
being blind since the age of ten months, he fell into a state of melancholy. He was unable
to function in a visual world after learning to work his way around by touch and hearing.
As a result, he became less confident and more disappointed in the world, which seemed
a “drab place.” Human beings’ knowledge of reality also can be decided by early
experiences in life.
“The Nervous System and Behavior”
The cells that make up the nervous system are called neurons, typically consisting
of a cell body (containing the nucleus), an axon with synaptic processes, and dendrites.
Dendrites send information to the cell body which in turns sends information along the
axon. Providing insulation and metabolic support for nerve cells are glial cells. The two
divisions of the nervous system are the central nervous system (the brain and spinal cord)
and the peripheral nervous system (all nerves connected to the CNS). A neuron sends
information by using action potential. Initially, the neuron at rest is negatively charged,
called resting potential. When the neuron is stimulated, ions move across the membrane
of the neuron, temporarily changing the charge of the neuron during a phase called action
potential. This action potential is transmitted down the axon to the synapse. If the
synapse is a chemical synapse, the nerve impulse is transmitted via neurotransmitters.
With an electrical synapse, where neurons are closer together, the action potential of the
presynaptic neuron provides enough current to stimulate the postsynaptic neuron and
create action potential. Bilaterally symmetrical nervous systems have evolved though the
process of cephalization, the evolution of a head region where sense organs are
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concentrated. The evolution of vertebrates is marked with the enlargement of the CNS
and further cephalization.
“Intelligence”
Split twin studies have always been an essential part of the study of the
heritability of intelligence. Studies have shown that intelligence in split twins is very
similar, despite lack of shared environment. There are a few ways in which science
determines whether a trait is genetic or not. The direct method determines a correlation
between genetics and intelligence by studying split twins. According to this method,
about 74% of intelligence is genetic. The indirect method compares similarities in
intelligence between identical twins raised together and fraternal twins raised together.
According to this method, about 54% of intelligence is genetic. There is a great deal of
room for error in both methods. As a result scientists speculate that the actual heritability
of intelligence is somewhere between 30% and 70%. Studies also suggest that
heritability of intelligence could increase as people age. While the environment and
genetics are both important in the formation of intelligence, studies suggest that genes
continue to contribute as people grow older. Some scientists also speculate that the
heritability of intelligence may vary with the degree of intelligence. Mathematical
models are also being used to try to determine the heritability of intelligence. According
to one mathematical model used, the heritability of intelligence is between 47% and 58%.
After examining mathematical data, some scientists conclude that the average genetic
influence on intelligence is around 60%. This means that the environment accounts for
about 40% of intelligence. One important environmental influence on intelligence is
socioeconomic status (SES).
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“Nature and Nurture”
C.D. Darlington, a geneticist, suggested that genetics contribute to environment.
In some ways, people are able to choose aspects of their environments, and those choices
are often influenced by genetic preferences. This only works to a certain degree because
not all aspects of environment are chosen, some are imposed. During the beginning of
the century, scientists were often divided between extreme hereditarianism and extreme
environmentalism. Today, most scientists agree that both heredity and environment play
a role in behavior. The main question of the nature-nurture debate is how much
environment and heredity influence actions of the individual. Behavior research has
focused mainly on how much environment and genetics influence behavior and not how
they influence behavior because the issue of “how much” is far easier to address than
“how.”
“The Murder of a Child”
Characteristics of mankind are greatly influenced by the limbic system. There are
many behaviors influenced by the limbic system, such as Xenophobia (fear/hatred the
unfamiliar), that can be observed cross-culturally. However, while every culture may
exhibit Xenophobia, the way in which Xenophobia is expressed varies from culture to
culture. Basically, the emotion is determined by the limbic system and expression is
determined by culture. Using this idea, many scientists have come to the conclusion that
systems of values are probably influenced by the emotional programming in the limbic
system.
One of the biggest dilemmas with Darwinism is the evolution of the brain.
Science, so far, has had problems explaining why the human brain has advanced so far
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beyond the requirements of primitive man. One possible solution developed is that at
some point, culture became a more important evolutionary factor than biology. The
importance of culture may have been realized when humans began to realize that what is
best for the individual may not be best for the group. In this case, individuals are forced
to go against their own limbic system and personal desires to meet the needs of the group.
When a people go beyond biological norms, they often are forced to work very hard and
pay a price. Vegetarians, for example, are required to put far more work into planning
and knowledge of their diet than typical meat-eating people are required to do.
Another question involving the evolution of the brain is when the majority of
evolving took place. In most animals, the brain enlargement was reached early in
evolution and maintained to the present day. However, the human brain went through the
greatest amount of evolution and growth in the past two hundred and fifty thousand
years. While scientists are still investigating the mechanisms behind the evolution of the
human brain, they do know that the brain most likely evolved due to changes in the
environment toward a temperate climate as opposed to a tropical climate. Humans
moved to a savannah grass habitat and evolved in response to the new surroundings.
When humans began to walk on two legs, their hands were freed up to work with tools.
Inventions, such as the wheel, would be rewarded because they would assist the
community. As a result, such analytical thinking would become favorable. Hunting
skills would still be essential, so both traits would be encouraged.
“Genetics and Behavior”
Genetic scientists are using several techniques to establish genetic connections
with different traits in different organisms. Inbred mouse strains are being used to
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determine possible genetic preference for alcohol. Inbred strain comparisons are used
primarily to establish a behavior is genetically related, not to identify genes associated
with the trait. Open field tests have been used to study certain types of behavior in mice,
such as exploratory and emotional behavior. After testing, an allele was identified that
affects both exploratory and emotional behavior and coat color. Another type of test used
in genetic testing is done by developing a strain that expresses a genetic behavior and
seeing if that behavior can be passed to another strain that did not previously display the
behavior. In one experiment, strains of both maze bright and maze dull rats were
established. After several generations, scientists observed that the dullest of the maze
bright rats were still brighter than the brightest of the maze dull rats. A similar
experiment was conducted involving geotaxis in Drosophila flies. This experiment
suggested that geotaxis in Drosophila is controlled in a polygenic manner. Scientists
often use animal models to examine human polygenic traits and identify behavior genes.
By using such animal models, it is easier to control population, mating, and surroundings.
Studies have also been conducted on possible genetic ties in mating preference in
Drosophila flies. Scientist Margaret Bastock has observed that the yellow mutant gene
affects the pattern of male courtship. Other behaviors in Drosophila flies that have
mutant genetic ties include visual behavior, learning, movement, and stress response. By
analyzing behavior in Drosophila flies, scientist now have a new understanding
functional mechanisms in the nervous system as well as genes involved in learning.
Behavior in humans is often difficult to study because scientists are unable to use them as
genetic test subjects and human behavior is difficult to define and greatly affected by
environment.
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Oftentimes genetic disorders in humans result in abnormal behavior by targeting
the CNS and altering operation or structure. One example of such a disorder is
Huntington disease. More than one gene is often responsible for a genetic disorder.
Mood disorders and schizophrenia are examples of polygenic traits that are greatly
influenced by the environment. Scientists are attempting to use transgenic animal models
of some diseases (especially HD) and to use microarrays in polygenic disorders (such as
schizophrenia). With microarrays, it is possible to observe changes in more than one
gene at the same time. The findings microarrays may provide will make it easier to
develop transgenic animal models for polygenic disorders.