Genetics Essay

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It has often been suggested that genes have an influence on human aggression. Twin and adoption studies have often been used to determine the influence an individual’s genetic makeup has over aggressive behaviour. For example, Rhee and Waldman conducted a meta-analysis of twin and adoption studies on antisocial behaviour. They found that identical twins (share 100% genes) were more similar in anti-social behaviour than fraternal twins (50% share). This supports the theory that genetics influence aggressive behaviour, even allowing for the more closely similar environment of identical twins compared with fraternal twins. Also, Mason and Frick did a meta-analysis of 12 twin studies involving 3795 twin pairs. They concluded 50% of the difference between anti-social and non-antisocial behaviours could be attributed to genetics, with larger estimates of genetics found for more violent behaviours than for less violent behaviours. However, not only do Mz twins share genes but also share an environment that frequently treats them more similarly than it treats Dz twins. They are not perfect experiments. Court-Brown found that of a sample of 314 patients in a high security hospital, 15 had chromosomal abnormalities, including 9 who had extra Y chromosomes. Since the Y chromosome is the male sex chromosome and the incidence of XYY in the general population is 1 in 1000, this suggests that having an extra Y chromosome may have predisposed these men to increased aggressive behaviour. Concluded that those with XYY would be best kept hospitalised due to an increase likelihood of aggressive behaviour. Further research into the XYY karotype has revealed that although XYY people are on average taller than the general population, there is no evidence of increased aggression (Milunsky 2004) or higher testosterone levels (Ratcliffe et al). This suggests that the XYY karotype may not

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