Genetic factors in aggression Flashcards
How have twin studies demonstrated a genetic factor in aggression
Studies have found that nearly 50% of the variance in direct aggressive behaviour can be attributed to genetic factors
How have adoption studies demonstrated a genetic factor in aggression
A study of over 14,000 adoptions in Denmark by Hutchings and Mednick found that a significant number of adopted boys with criminal convictions had biological parents, particularly fathers, with convictions for criminal violence
What research has been done on the genetic factors in aggression
A meta-analysis by Rhee and Waldman combined the results of 51 twin and adoption studies and concluded that aggressive anti-social behaviour was largely a product of genetic contributions. However variables like age of participant and assessment method moderated genetic influence of aggression in some studies, suggesting that the influence of other factors than genes influence the genes expression
Who a meta-analysis of 51 twin and adoption studies
Rhee and Waldman
Who did an adoption study on over 14,000 adoptions in Denmark
Hutchings and Mednick
What gene has been associated with aggression
A gene producing an enzime called monoamine oxidase A (MAOA).
What does monoamine oxidase A do
It regulates metabolism in the brain, and low levels of serotonin are associated with aggression. A dutch family in the 80’s had a large proportion of it’s male members involved in violent crime, and the men were found to have abnormally low levels of MAOA in there bodies, with the defect in the gene later identified
What are the two types of MAOA
MAOA-H - A variant of the gene associated with high levels of MAOA
MAOA-L - A variant of the gene associated with low levels of MAOA
In a study by Caspi with 500 kids, those with MAOA-L were significantly more likely to grow up to exihbit anti-social behaviour but only if they were mistreated as children
Who studied 500 kids for their MAOA
Caspi
Describe the ‘Warrior gene’
MAOA-L is much more frequent in populations with a history of warfare, with about two thirds of people in these populations having a version of this gene. In contrast only one third of people in western cultures have MAOA-L. This has been referred to as the warrior gene
Why is sampling an issue for studies into genetics of aggression (eval)
Many studies have focused on individuals convicted of violent crime.
-The first problem with this is that convicitions of violent crime are relatively few compared to the vast number of violent attacks by individuals that are not convicted. They therefore represent a small minority of those regularly involved in aggressive behaviour.
-Secondly, those offenders designated as ‘violent’ in court are not necessarily the most serious, persistent offenders. For example a convicted murderer would be designated as violent on one offence with no history of crime.
These could explain why many studies show no evidence of heritability
What are the difficulties in determining the role of genetic factors (eval)
-More than one gene contributes to a behaviour
-There may be environmental influences on the manifestation of aggressive behaviour
-These influences may interact with one another, e.g genetic factors may influence environmental ones
What are the problems with assessing aggression (eval)
Many studies of aggression have relied on either parental or self reports, whereas others have used observational techniques. Miles and Carey did a meta-analysis, and mode of assessment was found to be a significant moderator of aggressive behaviour in the 24 studies analysed. They found that genetic factors explained a large proportion of the variance in aggressive behaviour in studies that used parental or self reports. However those that used observational ratings showed significantly less genetic contribution and greater environmental influence
Who did a meta analysis finding that the results of genetics depended on how you rated aggression
Miles and Carey
How might the MAOA gene explain gender differences in aggression (eval)
Niehoff suggests that gender differences may be a consequence of a genetic vulnerability that males and females have to the MAOA gene. The gene is linked to the X chromasome, and women have two of them, whereas men only have one. When men inherit the MAOA gene linked to the x chromasome from their mothers, they are more likely to be affected by it, but women may not be affected by an abnormal MAOA gene as they have a backup
Who suggested that the differences in chromasomes may result in genetic vulnerabilities in the MAOA gene between genders
Niehoff
