Genetic factors

• What are genetic factors?

  • No individual gene has been responsible for aggression but a gene called MAOA (monoamine oxidase A) is responsible for metabolism of monoamines such as serotonin in the brain. 
  • Different forms of the MAOA have been evident but a low activity one called (MAOA-L) has been found to cause abnormal levels of serotonin.
  • This links with impulsive or aggressive behaviour. It is known as the warrior gene. 
• Dutch family study?

  • In 1980’s, a Dutch family found that many of its male members behaved in a particularly violent way and were involved in many crimes of violence and rape.
  • They found lower levels of serotonin, which had to do with the low level of the MAOA-L gene. 
  • The aggressive gene seems to only affect the problems from their X chromosomes from their mother.
  • Even though women can inherit the gene, they don’t show aggressive symptoms as they have a second X chromosome carrying a good copy of the gene
• Supporting twin study?

  • Evidence for the role of genes in aggression.
  • Comes from twin studies comparing DZ twins to MZ twins.
  • MZ twins share 100% of genetics but DZ twins share 50% of their genes.
  • If MZ twins are more alike in their aggressive behaviour, it is due to genes rather than environment.
  • O’Connor found that concordance rates for MZ twins reared together was 72% compared to 42%.
  • Both MZ and DZ were reared apart, MZ = 64% and 34% for DZ twins.
  • This suggests a role for genes because the MZ's are higher than DZ but concordance rate is never 100%, aggression can't be genetic.
• Reductionist?

  • Aggression is caused by genetic influences and focuses on nature.
  • Environmental factors needs to interact with genetic ones to produce aggression.
  • Longitudinal study of 1037 children over 25 years - Caspi (2002) found males maltreated in childhood were likely to engage in anti behaviour, including violence in adulthood if possessing MAOA- L
  • Maltreated males with MAOA-L were 2x as likely than ones with MAOA-H to have conduct disorder and 3x to go to prison by 26 of violennce
  • Maltreatment nor MAOA predicted aggression but both did, interaction causes aggression (diathesis)
• Determinism?

  • We do not have free will over our behaviour.
  • leads to implications for crime and punishment.
  • In 2007, Bayout got convicted of stabbing and killing, being sentenced for 5 years and 2 months but his sentence reduced due to the finding that he had the MAOA-L gene.
  • Should criminals be granted leniency if they have faulty genes or should they be locked away forever as we cannot control it?
  • This research is socially sensitive and leads to ethical dilemmas where we would have unborn infants tested for aggression.
  • This type of ethical thinking illustrates behavioural genetics.
• Methodological issues?

  • The methods of measuring aggression differ between studies.
  • Criminal convictions, self-report, teacher/parent reports have all been used.
  • However, the results differ depending on the method used, a meta-analysis of 51 twin and adoption studies found that self-report studies found higher genetic influence than studies which used prent/teacher reports.
  • If research findings vary depending on how aggression is used, it is difficult to draw valid conclusions about the role of genetic factors in aggression.