Genetics

Aggression based on genetics is a biological approach which suggests that beahaviour is pre-determined through our genes, ignoring the role and influence of social factors.

There is a large amount of research which shows that aggression is primarily influenced by genetic factors. It is clear that our genes determine how much testosterone and oestrogen is produced and how sensitive our receptors are to it.

One method into studying aggression in genetics is through heritability studies.

Turner found that aggression in pigs is a heritable trait which can be passed on from parent to offspring.

Lagerspetz found that genetic factprs do not absolutely determine aggressive behaviour, but environmental factors are also important. Animals such as big cats can be taken from the wild and conditioned to be less aggressive suggesting that there is some control over aggression levels.

Psychologist chose to study identical twins for research into genetic factors due to them being genetically identical and any similarities in aggression will be caused by genes and any differences through environmental stimuli.

Canter found a correlation of 0.14 for MZ twins reared together and levels of aggression where O'Connor found a correlation of 0.72.

Miles and Carey carried out a meta-analysis of twin and adoption studies and found a heritability measure of aggression of 50%

Waldman et al, meta-analysis. the variability was due to the use of different methods in assessing aggression levels..

Early theories have focussed on XXY syndrome, where aggression was prevalent in males who have an extra Y chromosome.

Jacobs found that when studying men in instiutions 3% had XXY syndrome compared to only 0.1% in the general public. Individuals with XXY sydrome tend to be taller, have higher testosterone levels and lower intelligence which overall equates to aggression.

However, more recent research has disproved this theory. Wilkin found no link between an extra Y chromosome and aggression. XXY syndrome does equate to lower intelligence and so a higher likelihood of crime.

The theory cannot be discounted as due to low aggression brought with the extra Y chromosome the person gets agitated more easily and so are more likely to show aggression as they lack the skills to deal with stressful situations. This however may be better explained through SLT as they learn how to act aggressively in stressful situations.

Specific gene for aggression. Relationship has been found between MAOA and aggression. The gene breaks down serotonin, noradrenaline and dopamine which are all related to mood. If the gene does not work effectively then there is a build up of hormones causing a person to respond excessively to certain situations.

Brunner carried out a study on a dutch family and found that the Low MAOA gene is passed from females to males. Family records showed a history of violence in relation to stressful events.

Studies on mice have found that when the MAOA gene is disabled, male mice become aggressive, however there was no effect on females.

There is a great deal of research to support that aggression is genetically controlled. However, most believe that genetic factors do not work in isolation but alongside other factors.
Capsi studied 3 groups of males.

1. Mistreated as a child = anti-social behaviour

2. MAOA-L gene = conduct disorder and 3x more likely to have been convicted of violence

3. MAOA-L gene and mistreatment = most aggressive 44% of crime.