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Genetic Explanations Aggression

The main ways the role of genes in aggression has been examined is through the use of Twin Studies, Adoption Studies and looking at Individual Genes that may play a role. In twin studies; identical twins are compared between nonidentical twins for levels of aggression between them. This is because identical twins share the exact genetic makeup as each other while non-identical share only up to 50%. If identical twins have more similar levels of aggression then it is thought to be due to genetics.

McGuffin et al found that when studying sets of identical and non-identical twins; Identical twins aggression levels correlated more highly at 87% compared to non-identical twins that correlated 72%.On first glance this appears to support the basis of genetics being behind such similarities as aggression is shared more closely with those twins with identical genetics suggesting shared genes may be responsible.

However what is important to note here is that non-identical twins also had high levels of similarity in aggression levels and this could be argued to be due to the environment and learning similar aggressive behaviour. Therefore the family environment may also play a huge factor.

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Genetic Explanations Aggression

Adoption Studies have looked at examining levels of aggression between adopted children and that of their biological parents. If a positive correlation is found between adopted children and their biological parents then a genetic effect is implied. If a positive correlation is found between the adopted children and their rearing family; a environmental effect is implied suggesting aggression may be due to learning.

Hutchings et al conducted a study of reviewing 14’000 danish children who had been adopted. They found a significant positive correlation between the number of convictions for criminal violence among the biological parents and that of their children who had been adopted. This appears to add weight to the argument that genetics is behind such behaviour and such genes may have been passed onto their children.

However it must also be noted that the environment could be a factor here with adopted children having a more difficult time adjusting to their environment, learnt behaviour from biological parents previously or even the stigma that is attached with being adopted affecting how they are treated by friends, family and even how they view themselves.

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Genetic Explanations Aggression

Another major problem with such twin studies is that finding large numbers of identical twins who are reared apart is extremely rare to compare differences and most studies rely on comparing identical and non-identical twins.The problem here is that non-identical twins are likely seen by family, friends and those around them as actual individuals and thus treated as such. Identical twins may however be treated in exactly the same way as they are perceived to be the same by those around them; making their behaviour in turn similar due to exposure of the same things in the environment. Therefore the argument here is that such similar behaviour can actually be due to learnt behaviour and not genetics.

Also with Hutchings study, it could be argued to have cultural bias as the sample of children and parents were based only on Danish people and may therefore findings may not generalise to other cultures.

Individual genes have also been examined and some candidate genes have been identified that may play a role. MAOA is a gene that regulates the metabolism of Serotonin which low levels of such have been associated with aggressive impulsive behaviour. A faulty variant of the gene however could result in low levels of serotonin and thus lead to such aggressive behaviour

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Genetic Explanations Aggression

Brunner et al conducted a breakthrough study examining a dutch family who had a history of many of its male members involved with serious violent crimes (****, Arson). Studying them low levels of MAOA were found and later a defective gene was identified in the male members. This seems to add much weight to the argument that genetics could be at work and lead to some people being more prone to violence due to certain genes.

However such similar behaviour could also be explained due to similar exposure and learning from role models within the family influencing such behaviour through the principles of social learning theory and observation and imitation. Only male members were tested and found to generally have aggressive traits however none of the female members were checked nor were they commonly found to have aggressive tendencies despite having a 50% chance of carrying the gene. Again the results remain inconclusive.

Caspi et al found evidence that may clarify such and offer an alternative view and how genes actually interact with the environment studying the MAOA gene which is involved in Serotonin metabolism. Studying 500 children, one half were identified to have high levels of MAOA while the other were identified to have low levels of MAOA. Those with low levels were associated with higher levels of aggression however only if they were maltreated previously. Those with high levels of MAOA and were mistreated and those with low levels of 

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Genetic Explanations Aggression

and were not mistreated did not exhibit any anti-social behaviour. This suggests that faulty genes may increase the possibility of aggression however there needs to be psychological stressors too to activate such.

Issues, Debates and Approaches.

Reductionist – Theories which propose genes alone as responsible for aggression as reductionist as they do not take into account cognitive, psychological or cultural factors simplifying aggression down to genetics which people have little control over.

Deterministic – This is therefore Deterministic in assuming genes control people and they have little ability for free will or conscious thought which is clearly possible by people. People have the ability of free will and making their own decisions and those found to have “aggressive” genes are not always found to be aggressive.

Methodological problems – Much research into genes and aggression is based on correlation data such as the studies mentioned. The problem with this is we cannot infer cause and effect with correlation date as many unknown variables may exist in between that contribute to the results.

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