The Contribution of Genetics and the Environment to Personality Development.

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The Contribution of Genetics and the Environment to Personality Development.

The Nature Vs Nurture debate has been an integral question that has influenced many divisions of psychology, including personality theory. Some theorists have focused on the side of genetic determinism, whilst others have placed a greater emphasis on the role of the environment, however the debate is in itself a false dichotomy. The existence of monozygotic and dizygotic twins, as well as adopted children has allowed psychologists a unique method of untangling the influences of genes and the environment on personality. The results of these studies indicate that the environment and genetics are not mutually exclusive factors in determining personality, their interaction is consequently what produces unique individuals. Behavioural geneticists while striving to determine the genetic aspects of personality have ironically played a major role in helping to uncover environmental influences on personality. (Plomin, Ashbury, Dip & Dunn, 2001; Loehlin, 2010). The environment can be split into two distinct categories; shared and unshared. The shared environment consists of any mutual experiences that siblings have encountered which distinguish them from the general environment. This can include such factors as gross family income, relatives, and the home environment. Conversely the unshared environment is the differences that siblings from the same home experience, such as differential treatment from parents, distinctive friends and hobbies. (Maltby, Day & Macaskill, 2010). In contrast to socialization theorists who believe that the shared environment is what contributes to similarity in personality amongst siblings, behavioral geneticists have found that shared heritability is what influences similarities whilst the unshared environment is what encourages personality uniqueness. (Plomin et al., 2001) The shared environment has been questioned as having little relevance to the personality similarity found between siblings. Studies of twins reared apart provide evidence for the lack of influence of the shared environment. (Dilalla, Gottsman, Carey & Bouchard, 1996; Pederson, Plomin, McClearn, & Friberg, 1988; Tellegen, Bouchard, Wilcox, Segal, Lykken & Rich, 1988). As these twins have different experiences in their shared environment it suggests that the unshared environment and genetic heritability are the more important factors in contributing to personality. In Pedersen et al, (1988) study, they found through comparison of twins reared together and twins reared apart, that the shared environment accounted for a mere 10% of similarity in personality. Correspondingly, adoptive families also provide insight into the breakdown of personality similarity. Unrelated adoptive siblings only have in common the shared environment, thus looking at the correlation in their personality traits can provide insight into the impact of shared environment on personality. Loehlin (1992) found that a correlation between adoptive siblings was .02, thereby proposing no significant influence of the shared environment. Interestingly though Rose, Koskenvuo, Kapriio, Sarno and Langinvainio (1988) found that increased social interaction between twins contributed to greater correlations in personality traits of Neuroticism and Extraversion. These findings challenge the notion that shared environments do not significantly affect personality similarity in siblings. However although this finding is noteworthy it only looks at association between the factors of interaction and personality, not causation. Rose et al. (1988) acknowledge that perhaps these findings are evident due to an interaction effect between genes and environment. Twins who are more genetically alike may choose to spend more time together, therefore increasing their shared environment. The environment is important in shaping personality, however it does not contribute to...
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