discuss the evidence for biological influence on personality

In the early 1900s, Edward Thorndike decided to do comparative studies of twins, siblings, and unrelated individuals of family histories and school eliminations. The findings convinced him that the main factor that influences our personality is genetics. However, John B. Watson (1925) claimed that he could train any healthy, well-formed infants in his own specified world to become any type of specialist he might select. This essay will be looking into the evidence for genetic influences on personality, mainly focusing on twin, adoption, and family studies.

Twin studies play a very important role into determining whether or not personality is genetically influenced. Identical twins are siblings who share 100 percent of genes with each other. They are more or less the best participants to prove whether or not personality is genetically influenced. Fraternal twins share 50 percent of genes with each other. They are excellent participants to compare with identical twins. Twin studies generally rely on findings of identical and fraternal twins; if identical twins have more similar behaviour than non-identical twins then this provides evidence for genetics influence on personality. James Olson et al. 2001) looked at whether attitudes are genetically influenced by evaluating earlier studies and also carried out research on identical and fraternal twins. While traditional psychological theory claimed that attitudes are learned and mostly influenced by environment, Olson et al. and colleagues argued that biological and genetic factors also influence attitudes. They assumed that genes perhaps influence natural inclinations, then environmental factors will develop different traits and attitudes. Another interesting study by Amy Abrahamson, Laura Baker, and Avshalom Caspi (2002) looked at the genetic influences on attitudes of teenagers.

The idea of their study was to investigate causes of family influence on teenagers’ social attitudes in order to understand whether and how much families influence the attitudes of them. Abrahamson, Baker and Caspi (2002) wanted to discover the age when genetic influences come to view and to look at how much parents and siblings affect the teenagers’ views on contractive issues. Genetic influences in social attitudes were being investigated in 654 adopted and nonadopted children. From the age of twelve to fifteen, children were annually measured for their conservatism and religious attitudes.

During the twelve year old visit, parents were also being measured. The study showed that shared-family environmental factors strongly influenced both conservatism and religious attitudes. Families’ similarities for conservative attitudes occur from both genetic and environmental factors, and religious attitudes are mostly influenced by family environmental factors. Compare to the findings from the twin studies before, this study by Abrahamson, Baker and Caspi (2002) suggests that until adulthood, genetic influence on social attitudes do not occur.

However, the Colorado Adoption Project study identifies that genetic influence in conservatism happens since the age of twelve, but there was no evidence on genetic influence on teenagers’ religious attitudes. Abrahamson, Baker and Caspi (2002) concluded that genetic factors influence social attitudes much earlier than they previously claimed. Adoption studies were also done to investigate genetic influences on personality. They are important because they include biological parents and environmental parents that affect differences in behaviour and personality. In the first adoption study on schizophrenia done by Plomin et al. 1997), the findings suggested that environment factors have very little influences on a child’s risk of getting disorders such as schizophrenia. During the study, interviews were given to both adopted children: the adopted children whose biological mothers suffered from schizophrenia and the ones whose biological parents did not suffer from any mental disorders. The finding shows that a number of the adopted children of biological mothers with schizophrenia also suffered from schizophrenia and the adopted children whose biological parents did not suffer from schizophrenia also did not suffer from it.

The study supports the theory that whether the biological parents or psychological parents raise the child, it does not increase nor decrease the chance of the child getting mental disorder. Moreover, another study which is also conducted by Plomin et al. (1997) proved that high percentages of the adopted children whose biological parents suffered from schizophrenia suffered from chronic schizophrenia or had symptoms similar to schizophrenia. Only a small numbers of the adopted children whose biological parents did not suffer from schizophrenia suffered from symptoms similar to schizophrenia and none of them suffered from schizophrenia.

This study again proved the genetic influences on personality. Nonetheless, regardless of numbers of study provided, genetics cannot be proved to be the only reason that causes schizophrenia or similar symptoms. Studies mentioned above only considered whether or not the children suffered from schizophrenia, many other factors such as development of the childhood were not accounted for. This decreases the reliability of the study to some extent. Through various studies, it has been shown that adopted children who are already biologically at risk are more likely to develop antisocial personality disorder.

Adopted children who are not biologically at risk do not normally develop the disorder while living in with their adoptive parents. It was also suggested that adopted children who both biological and psychological parents came from criminal backgrounds are more likely to develop antisocial personality disorder. However, since most of the adoption studies only used samples of the biological mother but not the biological father, a lot of factors and causes are being missed out such as which of the biological parents are more likely to pass the disorder to the children.

It is often difficult to make reliable conclusions on adoption studies because adopted children themselves display a higher rate of personality disorders. However, compare to the rest of families, adoptive family environment is generally better in terms of care, education, stability and health. Consequently, it is hard to determine what factor causes the development of disorders the most. Family studies usually look into the level of risk that family members carry mental disorders to relatives.

The studies compare how big the chances are for relatives of family members who suffered from mental disorders to also suffer from it than relatives of family members who did not suffer from any mental disorders. These studies are often conducted using molecular genetic studies. Linkage analysis is the most common molecular genetic study. An interesting study was carried out by Lilenfield et al. (1998) to investigate whether eating disorders were carried through family genetics. Participants whose relatives suffered from eating disorder and participants whose relatives did not suffer from eating disorder were both interviewed.

The interview included whether the participants themselves had eating disorders and if they were suffering from mood, anxiety and any personality disorders. The findings suggested that participants whose relatives suffered from eating disorder have a higher risk of developing eating disorders and depressive disorders. There was definitely a connection between participants who suffer from eating disorder and their relatives who also suffer from eating disorder. However, it cannot be proven that there is a link between participants’ risk of suffering from depressive disorders.

Relatives of suicide victims are more likely to develop suicidal behaviour; nevertheless, the cause of this behaviour is still uncertain. David A. Brent, Jeff Bridge, Barbara A. Johnson, and John Connolly (1996) carried out a study to investigate if suicidal behaviour is genetically influenced. Teenage relatives of suicide victims and relatives of similar teenagers were both examined for Axis I and II psychiatric disorders, lifetime histories of aggression, and histories of suicidal behaviour.

Relatives of suicide victims were more likely to develop suicidal behaviour and other psychological disorders. Also, participants who are more aggressive are likely to develop suicidal behaviour. However, relatives who share the same genes usually also live under the same environment which factors can be caused by environmental influences. Therefore, it is hard to rely on the findings of family studies. In conclusion, studies have provided sufficient evidences for genetic influences on personality. Twin studies indicated that identical twins have ore similar behaviour and personality than fraternal twins. There are also positive correlations between the adopted children and their biological parents which provide evidence of genetic influence. However, some factors are neglected in the studies which can affect the result of the findings. References Brent, D. A. , Bridge, J. , Johnson, B. A. , Connolly, J. (1996). Suicidal behavior runs in families: A controlled family study of adolescent suicide victims. Archives of General Psychiatry, 53, 1145-1152 Bergeman, C. S. , Plomin, R. , McClearn, G.

E. , Pederson, N. L. , & Friberg, L. T. (1988). Genotype-environment interaction in personality development: Identical twins reared apart. Psychology and Aging, 3, 399-406 Berrettini, W. H. (2000). Are schizophrenic and biological disorders related? A review of family and molecular studies. Biological Psychiatry, 48, 531-538 Brent, D. A. , Bridge, J. , Johnson, B. A. , Connolly, J. (1996). Suicidal behavior runs in families. A controlled family study of adolescent suicide victims, 53, 1145-52 Michael C. Ashton. Individual Differences and Personality

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