Aggression - Gentic Factors Flashcards
Explain twin studies and the findings that are produced.
MZ twins share 100% of their DNA and DZ twins share 50%.
Coccaro studied adult male MZ and DZ twins.
Concordance rates for physical assault was 50% for MZ and 19% for DZ.
Concordance rates for verbal aggression were 28% for MZ and 7% for DZ.
If the concordance rates are the same or very similar it suggests it’s how they’ve been brought up rather than a genetic basis. These results show some genetic basis.
Explain adoption studies in Agression
Hutchings and Mednick studied over 14,000 adoptions in Denmark. They found a significant number of adopted boys with criminal convictions had biological parents with convictions for criminal violence, showing a genetic link for aggression.
What does the MAOA gene do?
It regulates the metabolism of serotonin in the brain. It’s role is to mop up neurotransmitters in the brain after a nerve impulse has transmitted from one neutron to another. It does this by breaking down the neurotransmitter into constituent chemicals to be recycled or excreted. The production of this enzyme is determine by the MAOA gene. If this gene is dysfunctional it may lead to abnormal activity of the MAOA enzyme, which in turn effects the serotonin levels in the brain.
Study of a Dutch family, Brunner et al - The MAOA gene.
Brunner et al indicated a defect in the MAOA gene of a Dutch family whose male members behaved in violent and aggressive ways. A large proportion had been involved in serious crimes including rape and arson. They were found to have abnormally low levels of MAOA in their bodies.
Is the MAOA gene a gene for aggression?
A variant of the MAOA gene, MAOA-L has been named the warrior gene, it’s most frequent in populations with a history of warfare. 2/3 of these populations have this version of the gene. Only 1/3 of western populations have the variant of the gene.
Evaluation - Problems of Sampling
Many of studies in this area have focused exclusively on individuals convicted of violent crimes which causes 2 particular difficulties.
Convictions for violent crime are relatively few compared to the vast number of violent attacks that never result in a conviction. Therefore, he convicted ones represent just a small minority of those regularly involved in aggressive behaviour.
Evaluation - Difficulties of determining the role of genetic factors
The connection between genetic factors and aggression is far from straightforward because of problems determining what is, and what isn’t, a product of genetic inheritance. It’s difficult to establish genetic contributions to aggressive behaviour because:
- more than one gene usually contributes to a given behaviour
- As well as genetic factors, there are many non-genetic influences, ie environmental influences.
Evaluation - Evidence for the role of MAOA gene
Tiihonen et al (2015) studied Finnish prisoners, revealing that the MAOA low-activity genotype (MAOA-L) in combination with another gene (the CDH13 gene) was associated with extremely violent behaviour. There was no substantial evidence for either of these genes among non-violent offenders, indicating that this combination of genes was specific for violent offending only. However, critics argue that genes make it harder to control some urges but may not determine behaviour.
