Most individuals readily accepts that physical human characteristics such as hair color, skin color and height are controlled by genes. How ever the question of the importance of the genetic and environment all factor in the control of human psychological characteristics, such as behavior and intelligence, is more controversial. This question has a long history and is often referred to as the Nature vs Nature controversy. The question I s not whether the genotype has any effect; clearly genotype and environment both influence personality and behavior . The questions are how largely a contribution each make and which is the dominant influence. In Western society, the prevailing opinion has long been that behavior is most strongly influenced by environment. This implies that personality disorder has its cause in childhood experience. And societal influences, not in the genome. This controversy is hard to test scientifically because doing quantities genetics studies of human behavior is difficult. Large scale experiment involving controlled human mating cannot be made, nor is it possible to control the environment of human population. It is possible, however to study cases in which humans with identical genotypes are exposed to different environment by studying cases of monozygotic twins who have the same genotype in principle, all difference in behavior characteristics is for environmental influences, whereas similarities may result from genetic influences.
T.J Bouchard at the University of Minnesota performed an important twin study . Science 1979, Bouchrd has studied over 1000 pairs of monozygotic twins raised together(MZT) or raised apart (MZA). Twins participating in the study undergo over 50 hours of intelligence and psychological testing, the result suggest that genetics has large influences on intelligence and behavior. Calculation of H2 for IQ, for example suggest that more than 70% of the variance in IQ can be traced to genetics. Comparing MZA with MZT suggest that being reared together actually has only a minor effect on IQ . The together ness factor was more pronounced in childhood and early adolescence but declined greatly during adulthood.
Some of the most interesting result came from test measuring personality and behavior characteristics. For Characteristics such as aptitude , leisure time activities and vocational interest the twins showed a strong genetic influence, as largely as for IQ. No aspect of behavior was unaffected . Overall ,the genetics influence on all behavioral characteristics was been 50 and 70%. Major personality disorder (manic depression) also have significant genetic basis.
Individual study cases cannot be the basis for a strong conclusion. But taken together , the many cases suggest that genotypic differences may account for many, or even a majority of, the difference in behavior between individuals in human populations, including behaviors normally assumes to be under conscious control. It is becoming clear that the brain ,like other organs of the body , is strongly influenced by the genotype, and these influences may shape our behavior to a much greater extent than was previously believed.
T.J Bouchard at the University of Minnesota performed an important twin study . Science 1979, Bouchrd has studied over 1000 pairs of monozygotic twins raised together(MZT) or raised apart (MZA). Twins participating in the study undergo over 50 hours of intelligence and psychological testing, the result suggest that genetics has large influences on intelligence and behavior. Calculation of H2 for IQ, for example suggest that more than 70% of the variance in IQ can be traced to genetics. Comparing MZA with MZT suggest that being reared together actually has only a minor effect on IQ . The together ness factor was more pronounced in childhood and early adolescence but declined greatly during adulthood.
Some of the most interesting result came from test measuring personality and behavior characteristics. For Characteristics such as aptitude , leisure time activities and vocational interest the twins showed a strong genetic influence, as largely as for IQ. No aspect of behavior was unaffected . Overall ,the genetics influence on all behavioral characteristics was been 50 and 70%. Major personality disorder (manic depression) also have significant genetic basis.
Individual study cases cannot be the basis for a strong conclusion. But taken together , the many cases suggest that genotypic differences may account for many, or even a majority of, the difference in behavior between individuals in human populations, including behaviors normally assumes to be under conscious control. It is becoming clear that the brain ,like other organs of the body , is strongly influenced by the genotype, and these influences may shape our behavior to a much greater extent than was previously believed.
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