Lesson 3 - Genetic factors in aggression Flashcards
What extra chromosome can cause increased aggression in men?
XYY
What study found the XYY chromosome?
Court Brown’s study. He discovered 314 patients that had the XYY chromosome and claimed that they should remain hospitalised due to their increased aggression.
What was the concordance rate for aggression in MZ and DZ twins?
Coccaro studies pairs of adult male twins, and found that the concordance rate for aggression as in physical aggression was 50% in MZ twins, but only 19% in DZ twins.
What was the concordance rate for these twins for verbal aggression?
MZ: 28%
DZ: 7%
What were the results of adoption studies?
Rhee and Waldman carried out a meta-analysis of adoption studies for direct aggression and antisocial behaviour, and found that genetic influences accounted for 41% of the participants. This is combined with twin studies.
What is the MAOA gene?
It is responsible for the production of the protein monoamine oxidase.
It allows for the metabolising or noradrenaline, serotonin and dopamine.
Explain the MAOA-L gene.
This is the low activity version of the MAOA gene. This gene makes someone more likely to be aggressive. It is known as the ‘warrior gene’. Lea and Chambers found that it was possessed by 56% of Zealand Maori men (compared with 34% of caucacians).
What are the 3 neuro transmitters MAOA-L has an effect on?
Dopamine - High levels (rewards aggression).
Serotonin - Low levels (Lack of inhibition)
Noradrenaline - High levels (Overreaction to threats)
Evaluation of the genetic factors - Coccaro
Coccaro supports the role of genetics, because the concordance rate of physical aggression in the form of criminal behaviour for MZ twins was higher than DZ twins.
Evaluation of the genetic factors - Godar
Godar supports this, as they managed to refine selective breeding, by removing certain genes in mice. This was done by removing the MAOA gene. The mice then showed heightened aggression and abnormal levels of serotonin. However, when they were given fluoextine, and their serotonin levels rose, they returned to normal behaviour.
Evaluation of the genetic factors - Brunner
Brunner studied 28 men from a large Dutch family, who were repeatedly involved in impulsively aggressive violent criminal behaviour. All the men in this family possessed the MAOA-L gene.
Evaluation of the genetic factors - Stuart
Stuart studied 97 men who had been involved in severe domestic abuse cases. They found that the most violent of the men had a faulty MAOA gene. These men inflicted the most physical and psychological damage onto their partners.
Evaluation of the genetic factors - Theilgaard
Theilgaard counters the XYY gene concept. They investigated research into XYY men, and found that while it does cause an increase in height, it does not cause an increase in aggression.
Evaluation of the genetic factors - Twin studies lack validity
Every pair of twins share the same environment (as they are raised together), yet DZ twins may not share the same environment to the same extent as MZ twins. MZ twins are often treated the exact same way by people, whereas DZ twins may not be, especially if they are not the same sex. This means that they will have different environments, and this may cause a difference in later behaviour.
