Genetic influences on aggression
Genes do not directly cause aggression but influence elements of our biology that contribute to it. This can be demonstrated through the following methods; 1.Animal Breeding Studies In animal breeding studies, animals are selectively bred for certain traits. If it is possible to breed for aggression, this would suggest that genes contribute to aggressiveness. Lagerspetz (1979) bred 25 generations of mice. In each generation, she chose the least aggressive individuals to breed together and the most aggressive ones to breed together. The result was two very different strains. One group of mice were super-aggressive, the other very docile. Even when cross-fostered to nonaggressive mothers, mice from the ‘aggressive’ strain still demonstrated more aggression. This showed that there is, at least in animals, a genetic component to aggressive behaviour However, a problem with research on animals is that it is difficult to generalise the results to humans, nevertheless, mice are often used in genetic studies because their genes are homologous to those of humans, this means they produce the same proteins, which are used in a similar way. 2. Heritability Studies (Twin and adoption studies) Research on humans has also supported the notion that genes are an important factor in aggressiveness. Grove et al ( 1990) studied 32 sets of MZ twins who were separated and raised apart shortly after birth. A continuous score for anti-social behavior in both childhood and adulthood was derived by interviewing each subject with a standardised interview schedule; as such this assessment of antisocial behavior was a selfreport measure. Statistically significant heritabilities were obtained for anti-social behavior in both childhood (0.41) and adulthood (0.28). Rhee and Waldman (2002) conducted a meta-analysis of 51 twin and adoption studies. Aggression was measured (operationalised) through psychiatric diagnoses such as conduct disorder, criminal records...
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