Genetic Explanation

• Who proposed the idea that criminals may have an inherited characteristic?

  Lombroso
• What do genetic explanations suggest about offending behavior?

  That it is inherited as one or more genes predispose people to commit crimes
• What types of studies provide evidence for genetic explanations of offending behavior?

  • Twin studies
  • Adoption studies
  • Family studies
• What do twin studies help identify in terms of behavior?

  A genetic basis of behavior
• How do monozygotic (MZ) twins differ from dizygotic (DZ) twins in genetic studies?

  MZ twins share 100% of their genetic make-up, while DZ twins share 50%
• What were the concordance rates for offending behavior found by Christiansen (1977) for male MZ and DZ twins?

  Male MZ twins: 35%, Male DZ twins: 13%
• What were the concordance rates for offending behavior found by Christiansen (1977) for female MZ and DZ twins?

  Female MZ twins: 21%, Female DZ twins: 8%
• What do the low concordance rates for monozygotic twins suggest about criminal behavior?

  That the environment plays a significant role in criminal behavior
• What interesting question does the difference in concordance rates between male and female twins raise?

  The role of gender in criminal behavior
• What are two limitations of twin studies?

  1. Findings can't be generalized to a broader population due to lack of randomization.
  2. MZ twins may have genetic differences due to mutations after fertilization.
• What is a key criticism of genetic research in relation to environmental effects?

  It cannot rule out the effect of the environment on behavior
• What did Crowe (1972) find regarding adopted children and their biological mothers' criminal records?

  50% of adopted children with a biological mother who had a criminal record also had one by age 18
• What percentage of adopted children in the control group had a criminal record by age 18 according to Crowe (1972)?

  5%
• What do adoption studies aim to demonstrate regarding criminal behavior?

  • They aim to rule out the effect of the environment.
  • They examine children raised by adoptive parents with no genetic similarity.
• What genetic condition was identified in the family studied by Brunner et al. (1993)?

  Brunner syndrome
• What is the average IQ of the family studied by Brunner et al. (1993)?

  85
• What deficiency is linked to Brunner syndrome according to Brunner et al. (1993)?

  A deficiency in the MAOA gene
• What is a limitation of case studies like the one conducted by Brunner et al. (1993)?

  • They may lack generalizability due to the unique circumstances of the case.
  • They often focus on a small number of individuals, limiting broader conclusions.
• what is MAOA enzyme responsible for?


  breaks down neurotransmitters in the brain (serotonin, dopamine, noradrenaline)
• what happens if you have a low variant activity version of the MAOA gene?


  less MAOA to break down neurotransmitters, more serotonin, dopamine and noradrenaline
• how have scientists researched the MAOA gene in the lab?


  • mouse models genetically reproduced who have knock out MAOA (no MAOA) so mice became more hostile
• describe the Brunner study

  • females in family noted pattern
  • males were repeatedly aggressive, antisocial, had low IQ and had impulsive behaviours
  • repeated behaviour appeared across Netherlands, not just one family/group so shows it was due to genetics
  • genetic tests revealed aggressive individuals all shared unusual unavailable MAOA gene
  • combination of not having gene and context is necessary
• describe the Caspi et al 2002 study

  • followed 1000+ males age 3 to 26, closely following up with them
  • made sure that at the end they had 96% of people from original sample
  • strong longitudinal study
  • collected data about maltreatment between 3-11, variance of MAOA, reports of aggressive behaviour
  • found that maltreatment alone was a significant predictor of aggression, but not low activity of MAOA
  • combination of both was a significant effect on aggression