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Reinig 1 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 Reinig 2 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 Reinig 3 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). Reinig 4 “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 Reinig 5 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 Reinig 6 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. Reinig 7 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.