Genetic Influences on Personality free essay sample

Genetic influences appear to contribute significantly to the differences between people in personality’. Discuss. The research carried out in the field of behavioural genetics has indicated, over the course of many studies, that genetic influence has a direct affect on individual differences in personality. We will write a custom essay sample on Genetic Influences on Personality or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page Still, behavioural genetics has a lot to provide to the study of personality than inheritability predicts. This paper will discuss a few of the findings from research carried out on behavioural genetics in personality that go beyond the basic question; nature vs. nurture. The findings from the research include genetic continuity and environmental change during development, the impact of shared and non-shared environmental influences on personality and personality as a go-between of genetic influence on environmental measures. There are two general methods that have commonly been employed by behavioural geneticists investigating the genetic influence on personality: twin studies and adoption studies. Recently, there has been a surplus of behavioural genetic studies in the aetiology, particularly when discussing individual differences in personality. The results conclude that ‘Most personality traits show some genetic influence’; this has now become accepted within the study personality, (Plomin, DeFries, 1996). A very important discovery in genetic research on personality relates to the environment. It has been stated that genetic aspects are responsible for approximately 20 to 50% of the phenotypic variation in personality. The remaining variation is said to be the cause of environmental aspects. On the other hand, the study of twins and adoption find that shared family environments are accountable for only a small portion of variation in a majority of element of personality (Plomin, DeFries, 1996). It is important to note that there are a few aspects of this study that have grown to be quite complex. One of these aspects is the theory and research stating the differences between environmental influences on personality. First of all, a majority of researchers focus on comparing how shared and non-shared environmental aspects influence personality. Eysenck (1991) uggested that siblings or twins who shared environmental influences contribute only slightly to personality differences. Though an interesting point surfaced as a result of studies carried out by Plomin et al (1992); environmental aspects, unique (non-share) to family members, are influential over shared environmental aspects. Family personality is similar primarily due to the DNA which is shared with one another and not because of the shared family environments. This was established in a study of infants personality where a correlation was found for temperament to be about . 0 for genetically unrelated adoptive siblings—which provides a direct test of shared family environment—and . 20 for genetically related non-adoptive siblings (Braungart, Plomin, DeFries, Fulker, 1992). A question can be posed based on these results, if shared family environments do not shape personality, then what does? The answer lies within families and not between families. â€Å"The environmental influences that are important to personality are those aspects that are not shared by members of the same family—that is, environmental influences that are unique to family members† (Pedersen et al. 1992). These environmental influences (non-shared) make family members different from each another (Plomin Daniels, 1987). Non-shared environmental aspects could include differential parental treatment; differential extra familial relationships with friends, peers, and teachers; and non-systematic aspects such as accidents or illness (Plomin, Chipuer, Neiderhiser, 1994). The examination of environmental aspects that differ across families is not as beneficial to this study as the examination on environmental factors that differ within families. However, Reiss (1997) and Harris (1995), suggest that effects within-family pose problems when considering genetic heritability. The effects of children and parents can be under and over estimated; as a result it is vital to look into why each member of a family differ so much when it comes to personality. The solution will involve studying more than a single individual per family and discovering the association of experiential differences within a family with differences in personality. Harris (1995) has stated that non-shared aspects outside the family maybe more important in developing people’s personality. He explained the importance of non-shared environmental aspects by presenting the groups socialisation theory to determine personality. Social Learning Theory and Social Categorisation are the main elements of group socialisation. In social categorisation, similar individuals are placed into their in groups and individuals who are viewed as being different are placed within their out group. Harris utilised this concept to present how social groups can have an influence on people’s personality and how these non-shared environments that occur in children of the same family can have huge effects on personality. It has been possible to obtain encouraging results when associating non-shared environmental aspects to personality. For example, in the Sibling Inventory of Differential Experience (SIDE; Daniels Plomin, 1985), sibilings that had different experiences were linked with the personality differences in adolescence and adulthood (Baker Daniels, 1990; Daniels, 1986). However, it is not entirely correct to assume that shared family environments are unimportant to personality. For example, studies carried out on twins show considerable shared environmental influence for juvenile delinquency (Plomin, Thompson, 1995). Bouchard et al. (2003), in a study called the Minnesota Study of Twins Reared Apart, discovered that even when identical twins were bought up separately there was strong evidence showing similarities in personality. Bouchard also discovered that fraternal twins who are raised up separately do not show signs of similarities to the same extent as separated identical twins. Similarly, Pederson et al. (1988) stated that of 99 separated identical twins and 200 fraternal twins, in contrast to same numbers of non-separated identical and fraternal twins, separated twins had more dissimilar personalities. These results confirmed that identical twins reared apart appear to have more similar personalities than fraternal twins reared apart. Similarly, observational measures of shyness, activity, and aggressiveness show some shared environmental variation, whereas parent ratings of the same behaviours do not, but this was only the case during early childhood (Plomin, DeFries, 1994). Stein et al. (2002) observed the heritability of negative evaluation fears by using a twin sample (437 twin pairs aged between 18 and 86 years). Genetic correlations between twin scores on submissiveness, anxiousness and ocial avoidance aspects of a personality test were high. A study by Borkenau et al. (2002), testing 525 identical twins and 268 fraternal twins, reported that identical twins were more alike in their personalities than fraternal twins that were reared apart. These findings suggest the need for more observational research to assess the possible role of shared environment in personality develop ment. The challenge to personality researchers is to discover what non-shared experiences are relevant to personality change. There are, however, a number of recognised weaknesses within the method with adoption and twin studies. For instance, it is assumed that the adoptive children, their adoptive parents and their circumstances are mirroring the general population and, as a result, this flaw in the method of sampling leads to a bias which may cause researchers to underestimate or over estimate the genetic heritability across the whole population. Also, how can we be sure that people who adopt children are similar to those people who do not seek to adopt? Another problem with this method is the placement of the children themselves into an adoptive environment. Children who are placed with adoptive parents that are matched closely to their biological parents (as often happens) confuse matters further. Are the children behaving as they do because of their genes, sharing similar genetic makeup with their biological parents or because of environmental influences, as their adoptive parents are so similar to their biological parents. It would become difficult to answer this question. The wide range of concepts and theories of personality do state there to be stability from age to age, even in infancy, a period known to be of rapid developmental, (Costa McCrae, 1994). Not a lot is known, however, about the aspects that change in personality development. It is often assumed that stability is caused by genetic aspects and that environmental aspects are responsible for change. It would be incorrect to assume that the stability of personality is entirely associated with genetic aspects. It would be fair to state that stability can also be influenced by environmental factors, e. g. Freudians believed childhood experiences have a long term impact on personality. Conversely, it would be incorrect to assume the change in personality is entirely associated with environmental aspects. Genetic inheritance does not imply that there would be stability in personality this is due to the genes being dynamic in nature; altering in the amount and quality of their effects on the human as it, (Plomin, 1986). In recent studies of personality, it has been found that personality development throughout infancy is effected by both genetic and environmental change. An example of this can be seen in the MacArthur Longitudinal Twin Study (MALTS). It showed the stability of personality in over 300 pairs of twins, across 14, 20, and 24 year old. The results indicated that at these ages genetic influence was a key factor in the development of personality, (Saudino et al. , 1996). Furthermore, researchers came to an agreement on genetic links across age, suggesting that there was a very little change from 14 to 24 months. During this stage there were huge changes in the non shared environmental influences. The results obtained doing such a study has consistent with longitudinal twin studies of adult personalities showing that non-shared environmental influences are highly linked with personality stability (Bacon,Lykken, 1993). The finding that personality change, is due to non-shared environmental influences is, perhaps, not surprising. Adoption studies see if identical twins who have been adopted by different families differ in their personalities. If the researchers found that, even though the identical twins are separate, their personalities are similar this would suggest a strong reason to believe that biology has a huge role to play as opposed to environment in personality. The opposite is also true, that if they do have different personalities it is due to the environment as opposed to it being genetically inherent. In recent studies of behavioural genetics came to an unusual conclusion stating that genetic aspects provide considerably to many widely used measures of environment (Plomin, 1994). When this is looked upon as a phenotype in genetic analyses, â€Å"environment issues†, such as life events and social support frequently show as much genetic influence as measures of personality (Plomin Bergeman, 1991). The finding indicate that even though the environment has no DNA is has a direct implication and has genetic effects. The answer to this problem is not as controversial or vague as it seems: Genetic influences on measures of the environment are the result of variation with genetically influenced characteristics of the individual. The next step, then, is to identify those genetically influenced characteristics that are responsible for genetic variance on environmental measures. Genetic study of environmental and personality measures propose that personality traits contribute to a portion of genetic effects on environmental measures during infancy and adulthood. An example of this can be seen in the Swedish Adoption/Twin Study of Aging (SATSA). The genetic effects on Neuroticism and Extraversion were reported to contribute largely to genetic effects on measures of the current family environment (Plomin Nesselroade, 1993). These ‘super factors’ show approximately 20% of the genetic variation on two Family Environment Scales of personality. Studies on personality and self reports of life events concluded that all genetic variation on life events that were controllable were widespread to personality (McClearn, Plomin, in press). Reporting’s on life events stated that there were no unique genetic variation on personality, indicating that for adults, genetic influences on life events are entirely affected by personality aspects. What are the mechanisms by which personality traits come to mediate genetic influence on environmental measures? The answer is dependent on the degree to which the environmental measure is accurate. Plomin, 1986). When the self-report method is used to measure environment, there is the possibility that the responses to the questionnaire are not true results based on experience; instead it reflects ones individuals view on the environment. These personal views are sorted through their genetically influenced personality which would cause genetic variation between personality and environmental measures. However, if the self-reports were accurate and the major genetic variation between personality and the environmental measure were found then this would imply genotype–environment link, i. . , individuals are exposed differently to environments as a function of their genetically influenced personality. Using objective measures of the environment genetic links between personality and environments are not just â€Å"in the eye of the beholder†. For instance, in the Colorado Adoption Project (CAP) genetic effects based on observation/interview measurements of two infants (aged 2) home environments were governed mainly by genetic effects on task orientation that were free of genetic effects shared with cognitive development (Saudino Plomin, in press). The results that followed showed that infants’ environments reflect parents’ responses to genetically influenced attentional type of the infants. This discovery is important, as results show that in some instances the environment reflects rather than affects characteristics of individuals, the assumption made by developmentalists has been the opposite; where links between environmental measures and developmental outcomes are caused environmentally, it can now be shown that this is not the case. Behavioural genetic research has contributed much more to the study of personality than heritability estimates. In the past decade researchers have begun to document the importance of environmental factors on personality traits, track the developmental course of genetic and environmental contributions to personality and evaluate the role that personality plays in the line between nature and nurture. Also the method in which one conducts the research must be altered to attain more tangible results, for example, in current research behavioural genetics has used the self-report personality questionnaire for adolescents and adults, and the use of parent reports for children.