Discuss Genetic Factors in Aggressive Behaviour

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Discuss Genetic Factors in Aggressive Behaviour

Both twin an adoption studies have shown an important role for a genetic factor in aggression. For example, Cocker et al found that nearly 50% of the variance in aggressive behaviour could be attributed to genetic factors. Due to monozygotic (MZ) twins sharing 100% of the same genes, we would expect a higher concordance rate for their behaviour than Dizygotic (DZ) twin who only share 60%.

Research by McGuffin et al support this in their findings of an 87% concordance rate for aggression in MZ twins and a 72% in DZ twins. A concordant analysis by Christianson reinforces these findings. Of over 3.5k Danish twins he found MZ twins were more likely to be registered on by the police for criminal activity than DZ twins, especially males.  

Christianson’s research provides strong support due to the large sample size used. This means that it has high population validity and can be generalised to the population. Yet, it should be noted that they were all Danish twins and is subjected to cultural bias and lacks ecological validity and they cannot be generalisable to outside Denmark.

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Also, using criminality as a measure of aggression can be questioned as not all crimes are aggressive such as shop lifting. Therefore, it lacks sample bias.

Additionally, another weakness is MZ twins get treated alike because they look the same. Evans et al argued that findings within twin studies had low validity as MZ twins get treated in the same way which could contribute to aggression.

It should also be considered that results never showed 100% concordance rates in MZ twins which means that there must be other factors that contribute to aggression such as the environment.

Therefore research ...

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