Nature vs. Nurture
Psychologists have often questioned whether personality traits are inherited, and therefore a result of genetics, or if they are caused by the environment, and are therefore made. This has come to be known as the nature versus nurture controversy. Many psychologists throughout history have asked this question, and most agree the answer is both.
Nature versus nurture has been an on going argument for over a century and will carry on further. Scientists have been unable to conclude this question of which carries most responsibility for behavior. The argument of nature versus nurture is examined through the role of genetics in one’s personality. Then the role of environment in a one’s personality. Finally showing how both nature and nurture coincide to influence behavior in children, that the genetic makeup shapes one’s personality, thus determining how their environment is perceived.
Though one’s personality is not determined strictly by genetics, there is more evidence to support the idea that personality is inherited than there is to support the idea personality is made based on the environment and based on one’s experience. Many experiments and studies have been done to determine where one’s personality stems from, yet, few studies have been as effective as those studies based on twins, and adopted children. Both types of studies are extremely successful in determining where one’s personality comes from. In a twins study, the genes are regulated while in an adoption study the environment is regulated. Thus, question comes of introverted and extroverted personalities. (Plomin,1993)
One who is introverted is often thought to be someone that keeps to himself and rarely chooses to socialize in large groups. He is thought to be a longer and in many cases to lack the social skills necessary to enjoy himself in situations that are new to him. In reality, someone who is an introvert is simply more affected by stimuli than someone who is an extrovert. While an extrovert may be able to study in a noisy environment with many interruptions and distractions, an introvert is more likely to opt for a quiet corner of the library, free of extemporaneous noise.
A study was conducted that tested identical adult twins pairs that had been raised living apart from one another (Plomin, 1993). The twins were given self report tests to rate the extent to which they felt that they had grown up in an environment that was based around acceptance or rejection. In addition to testing these two traits, the extent to which their parents disciplined the twins was also tested. The reason for the self report tests to be centered around these topics because Plomin thought that it was important to determine a correlation between the environment one is raised in, and one’s personality.
Plomin tested 59 pairs of identical twins reared apart and 142 pairs of fraternal twins reared apart. What Plomin discovered was that traits once thought to be created based on the environment that one lives in, are really "influenced by genetic factors" (Plomin and Bergman, 1991). Many of the twins studied were said to have similar personalities, yet because they were raised apart, the only basis for the similarity is a genetic one. Though the twin studies were successful in proving that personality is in fact genetically based, many scientists were not convinced that one’s genes are the only factor that create one’s personality. Because "twins share the same womb, birth date and family, many possible environmental confounds were controlled" ( Plomin 1993) thus making adoptive studies a more accurate assessment of the inheritance of personality.
It has been hypothesized that adopted twins raised independent of their parents will develop a personality more similar to their adoptive parents than to their birth parents. The reason for this hypothesis is that many people assume that one learns who is and how one should act from the people living around them. Through extensive studies, Plomin (1993) was able to discern that adopted children are actually more similar to their birth parents than to their adoptive parents. Additionally, adopted twins reared apart are more similar to one another than similar to their adopted siblings. Though scientists have been able to conclude that genes do effect behaviors and personality, the question still remains what genes effect what behaviors.
Studies that look at the influence of genetics and environment on personality use of the concept of genetic similarity of siblings. By examining genetic similarity one can look at the differences in siblings as they grow up, with the knowledge that the subjects came from similar genetic backgrounds. Lynn, Hampson, and Agahi (1989) found support for the idea that traits are inherited in a study that examined Irish siblings. The siblings were not twins. The authors hypothesized that shared family environment has an effect on intelligence but not on personality. The study examined correlations between young Irish siblings in the areas of intelligence, neuroticism, extroversion, and psychoticism. 386 sibling pairs were used in the study. Using the Junior Mill Hill Vocabulary Test and a version of the Junior Eysenck Personality Inventory to measure these traits, the authors correlated the scores of siblings against one anothers. It showed that shared family environment does have and effect on personality, and it therefore supports that personality traits are a result of environment.
By comparing the level of extroversion in one child against his or her sibling, a correlation of .31 was obtained. This correlation is higher than the correlation predicted from the additive genetic model , which predicts the correlation predicted from the additive genetic model, which predicts the correlation between the siblings based only on their genetic makeup. This suggests that the difference is a result of some shared environmental factors, and these factors cause the siblings to more alike than the genetic model alone says that they should be. These environmental factors include the copying of each other by the siblings and the parents acting as socialization models. Although the siblings were found to have a high extroversion correlation when their levels of extroversion were compared as adolescents, this correlation decreased to .19 when they become adults and left home. These findings suggest that the drop from .31 to.19 is a result of the fact that after growing up, the socialization/observational learning effects diminish. In other words, siblings naturally influence one another while they live together, however this influence diminishes once they are separated. This study clearly shows environmental factors contribute to the personality characteristic of extroversion and it supports the argument that personality traits are a result of environment ( Agahi, Hampson, and Lynn, 1989).
McCartney, Harris, and Bernieri (1990), examine the developmental changes in twins by doing a meta-analysis of various twin studies from 1967 to 1985. Initially, the genetic makeup of the sets of twins was identified by determining if the twins were monozygotic, sharing all of their genes, or dizygotic, sharing about fifty percent of their genes. Then the differences within the genes of the twins were measured. With each set of twins, the study looked the correlations between the two with respect to intelligence, sociability, and activity. The results on sociability are the ones that are useful to us, as this characteristic is closely related to the trait of introversion/extroversion. To see what role, if any, environment plays in determining personality traits, the study then correlated sociability with the variables shared environment and non-shared environment to see if differences existed between the two. When all the pairs of MZ twins were used, those that had a shared environment, meaning that they grew up together instead of being separated after birth, had a correlation of .40. Those twins who did not share the same environment had a correlation of .33. When only the two twins with a mean age greater than five years of age were used, a difference of .22 was found. These differences suggest that the environment does influence sociability. The difference in the correlations does not suggest that environment is the ultimate factor in determining personality, but it does provide clear evidence that environment plays a role in affecting personality (Bernieri, Harris, and McCartney, 1990).
Stanley Greenspan, a clinical professor of psychiatry, behavioral science, and pediatrics at George Washington University Medical School, has been concerned with how parents can shape the personalities of their children. He proposes that some combination of genes and early and ongoing environment shape a childs personality. Greenspan’s work is not limited to one personality trait, but rather all personality types. He acknowledges that genes predispose children to a basic personality type. He also says that parents who are aware of their childs personality can create and environment for them that will help develop positive personality characteristics. For example, and aggressive, active child can become more aggressive, and possibly antisocial if his or her parents do not impose rather strict limits. This child can learn to deal with the aggressiveness in positive ways, such as expending his energy in physical activities, if the parents provide opportunity for the child to do so. This is just one example of how with an understanding of their children parents can shape the childs personality. Greenspan’s book the Challenging Child, which describes his work , provides additional support for the premise that environment plays a role in the development of one’s social development of one’s personality.
Personality traits are not set at birth. On the other hand, they are not caused completely by environment. The nature versus nurture argument will never have a clear winner, but the research this paper has found shows that genetics is not the only cause of personality traits. McCartney, etal. (1990) and Lynn, etal. (1989), showed that environmental factors played a part in raising the similarity between the two individuals in a pair of siblings. The work of Greenspan also shows that this is the case. This research show that environmental factors indeed play a part in developing one’s personality
The "Nature vs. Nurture" debate is summed up best when one says that is neither strictly the environment or one’s genes that determines one’s personality. It seems that one is given the basis for his personality through the genes that his parents pass on to him, yet this blue print for personality can be altered based on influence from the environment. "You are born with a certain temperament. But your experience in your early years, in you childhood, then ..modifies that temperament. It can change that temperament ...[A] child is born with a temperament that makes the child very bold, assertive, reckless, perhaps even violent, ..that.. dispositions can be changed through socialization" (Gergen and Gallagher 1996)
Thus it seems that while this "Nature vs. Nurture" argument is still somewhat unresolved there is more evidence based on twin and adoption studies that lead researchers and scientists to conclude that one’s personality is in fact inherited than there is to say that personality is made. While the environment plays a role in determining one’s genetic disposition, the world around a person never exclusively determines ones’ personality, but rather shapes his or her already existing disposition. The genetic makeup shapes one’s personality, thus determining how their environment is perceived.
Agahi, Hampson and Lynn (1989). Genetic and environmental mechanisms determining intelligence, neuroticism, extroversion, and psychoticism: An analysis of Irish siblings. British Journal of Psychology, 72-85
Bernieri, Harris, and McCartney (1990). Growing up and Growing Apart: A Developmental Meta-Analysis of Twin Studies. Psychological Bulletin, 107, 226-233.
Braungart, M., Plomin R., Defries,J., etal. (1992) Genetic Influence on Tester-Rated Infant Temperament as Assessed by Bayley’s Infant Behavior Record: Nonadoptive and Adoptive Siblings and twins. Developmental Psychology 28, 40-47.
Chipuer, H. Plomin, R. ,Penderson, G. etal. (1993) Genetic Influence on family Environment: The Role of Personality. Developmental Psychology, 29, 110-118.
Gergen, D. (1996, May) How Heredity and Experience Make you Who You Are. . Web-cr01.pbs.org [on line]. Available http://web- cr01.pbs.org/newshour/gergen/gallagher_5-14.html
Greenspan, Stanley. The Challenging Child. Reading, Mass: Addison- Wesley, 1995
"The Nature/Nurture Question " 1995 . \parInternet, available <http://homearts.com-
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