Role of Genetic Factors in Aggression Flashcards
What have twin studies told us about the role of genetic factors in aggression?
What did Coccaro et al study?
What did Coccaro et al expect to find?
What did Coccaro et al find?
Several twin studies have suggested that heritability accounts for about 50% of the variance in aggressive behaviour.
Coccaro et al studied adult male monozygotic (MZ) and dizygotic (DZ) twins.
Because MZ twins share 100% of their genes but DZ twins only share 50% (on average), we would expect to find greater similarities in aggressive behaviour between MZ twins if aggression is mostly influenced by genetic factors. This is because both MZ and DZ twins are raised together in the same environment, but MZ twins have a greater degree of genetic similarity than DZs.
Direct physical assault:
concordance rates of 50% for MZ twins and 19% for DZs.
Verbal aggression:
Concordance rates of 28% for MZs and 7% for DZs.
What have adoption studies told us about the genetic factors in aggression?
What did Hutchings and Mednick find?
What did Rhee and Waldman find?
Adoption studies can help to untangle the relative contributions of environment and heredity in aggression. If a positive correlation is found between aggressive behaviour in adopted children and aggressive behaviour in their biological parents, a genetic effect is implied.
A study over 14000 adoptions in Denmark found that a significant number of adopted boys with criminal convictions had biological parents with convictions for criminal violence, providing evidence for a genetic effect.
They carried out a meta-analysis of adoption studies of direct aggression and anti-social behaviour, a prominent feature of which is aggressive behaviour. They found that genetic influences accounted for 41% of the variance in aggression, more or less in line with the findings from twin studies.
How do genes cause aggressive behaviour?
What is MAOA and what does it regulate?
What happens when the operation of this gene dysfunctions?
What is the warrior gene?
A gene responsible for producing an enzyme called monoanime oxidase A (MAOA) has been associated with aggressive behaviour.
MAOA regulates the metabolism of serotonin in the brain, and low levels of serotonin are associated with impulsive and aggressive behaviour.
A dysfunction in the operation of this gene may lead to abnormal activity of the MAOA enzyme, which in turn affects levels of serotonin in the brain.
MAOA-L is much more frequent in populations with a history of warfare, with about two-thirds of people in these populations having this version of the gene. Contrastingly, only about one-third of people in Western populations have this low activity version of the gene. This has lead it being referred to as the warrior gene.
What did Brunner et al study and find?
What did Stuart et al study and find?
Brunner et al studied male members of a large church family who were repeatedly involved in impulsively aggressive violent criminal behaviour such as rape, attempted murder and physical assault. The researchers found that these men had abnormally low levels of MAOA in their brains and the lower activity version of the MAOA gene.
Stuart et al studied men who because they had been involved in inflicting intimate partner violence (IPV), were part of a batterer treatment program. Men with the low activity MAOA gene were found to be the most violent perpetrators of IPV. They engaged in the highest levels of physical and psychological aggression and inflicted the worst injuries on their partners.
How are gender differences in aggression supporting evidence of the role of genetic factors in aggression? (AO3)
Niehof explains that males and females have differential genetic vulnerabilities to the MAOA gene. The MAOA gene is linked to the x chromosome. When men inherit an x-linked gene from their mothers, they are more likely to be affected by it, whereas when women inherit the same gene they are generally unaffected (as they have a second x chromosome with a normal gene for MAOA that prevents expression of the abnormal version of the MAOA gene).
The fact that 18 to 24 year old men make up the greatest demographic in prison indicates this is a suitable explanation as it explains the uneven rate of aggression between men and women. This increases the external validity of the role of genetic factors as an explanation for aggression.
However, this explanation discredits the fact that women can also be aggressive.
How is nurture a limitation of the genetic explanation for aggression? (AO3)
Genetic explanation for aggression is in favour of nature in the nature/nurture debate. An example of the genetic explanation could be the warrior gene which involves a gene MAOA-L being frequently found in aggressive populations. This indicates aggression being an innate characteristic.
However, it could be argued genes are not enough to explain aggression as there needs to be a trigger such as abuse for the gene to result in aggressive behaviour. This is supported by the fact that Frazetto et al found an association between high levels of antisocial aggression and the low activity MAOA gene variant, as expected. However, this was only the case in those who had experienced significant trauma (such as sexual or physical abuse) during the first 15 years of life. This indicates that the diathesis-stress model could be a better explanation of aggression.
How can the deterministic approach of the genetic explanation for aggression be a limitation?
According to Morley and Hall, the knowledge that there is a possible aggression gene has interesting implications for the treatment of criminals and legal cases. Genetic explanations for aggression may result in criminals not being held responsible for their behaviour and actions as it pushes that idea that their actions are determined by genetic factors rather than their own free will. This can lead to lower charges and convictions which is beneficial for the perpetrator but not the victim. For example, Bradley Waldrop killed his wife’s friend with a machete. Instead of being convicted for murder which is punished with death penalty, he was charged with manslaughter which is punished with life in prison, due to the fact that he had the warrior gene. Therefore, this explanation could be limited as it doesn’t consider free will and responsibility.
