Genetic Factors in Aggression

• Who studied men who were monozygotic or dizygotic in 1997?

  Coccaro et al
• What is expected if aggression is influenced by genetic factors?

  Greater similarities in aggressive behaviour
• What were the concordance rates for physical assault in monozygotic twins?

  50%
• What were the concordance rates for physical assault in dizygotic twins?

  19%
• What were the concordance rates for verbal aggression in monozygotic twins?

  28%
• What were the concordance rates for verbal aggression in dizygotic twins?

  7%
• What did Rhee & Waldman (2002) conduct a meta-analysis on?

  Adoption studies of aggression and antisocial behaviour
• What percentage of variance in aggression is accounted for by genetic influences?

  41%
• What does the MAOA gene regulate in the brain?

  Activity of MAO-A
• What role does serotonin play in aggression?

  It is thought to influence impulsive aggression
• What is the low-activity variant of the MAOA gene?

  MAOA-L
• What is linked to high levels of aggressive behaviour?

  MAOA-L gene variant
• Who studied 28 men from a Dutch family with impulsive aggressive behaviour?

  Brunner et al
• What did the men in Brunner et al's study have abnormally low levels of?

  MAO-A
• What is the relationship between MAOA-L gene activity and adult aggression?

  It may relate to early traumatic experiences
• What did Frazzetto et al (2007) find about antisocial aggression?

  It is associated with MAOA-L and childhood trauma
• What was found in individuals without childhood trauma regarding MAOA-L?

  They did not have high adult aggression
• What are the evaluation points regarding the MAOA gene and aggression?

  • Research Support: MAOA-L linked to greater aggression
  • Environmental Factors: Non-genetic factors are crucial
  • Complex Link: Serotonin levels are disrupted, not simply low
• What did Mertins et al (2011) find about MAOA-H variant men?

  They were more cooperative and less aggressive
• How did participants with MAOA-L behave when aware of others' cooperation?

  They behaved cooperatively rather than aggressively
• What is a problem with twin studies regarding environmental factors?

  Dizygotic twins may not share environments equally
• Why might concordance rates in twin studies be inflated?

  Monozygotic twins are treated more similarly
• What does the assumption about twin environments suggest about genetic influences?

  Genetic influences may not be as great
• What is a strength for the Genetic Factors in Aggression?

  Research Support

  • The MAOA-L variant is associated with greater aggression
  • Mertins et al (2011) found that men with MAOA-H variant were more co-operative and made fewer aggressive moves compared to those with MAOA-L
  • This finding supports the relationship between MAOA gene activity and aggression
• What is a limitation for the Genetic Factors in Aggression?

  Environmental Factors

  • However, Mertins et al (2011) also showed that non-genetic factors are crucial
  • Participants with MAOA-L behaved cooperatively rather than aggressively when they were made aware that others in the study were behaving cooperatively
  • Therefore, genes are influenced by environmental factors that are at least as important in aggression
• What is a limitation for the Genetic Factors in Aggression?

  Complex Link

  • Research linked aggression with low levels of serotonin, but the MAOA-L gene causes low activity of the MAO-A enzyme which should lead to higher serotonin
  • In people with the MAOA-L variant, it may be more accurate to say that their serotonin levels are disrupted rather than they are lower or higher than normal
  • This shows that the relationship between the MAOA gene, serotonin and aggression is not yet fully understood
• What is a limitation for the Genetic Factors in Aggression?

  Problems with Twin Studies

  • In every pair of twins, both individuals share the same environment as each other, however dizygotic twins may not share their environment to the same extent as monozygotic twins
  • We assume they do, but this assumption may be wrong because one aspect of the environment is the way twins are treated by others, where monozygotic twins are treated more similarly than dizygotic
  • This means that concordance rates are inflated and genetic influences on aggression may not be as great as twin studies suggest