Genetic explanations

• Twin study by Lange (1930)

  -        Lange (1930) investigate 13 identical twins and 17 non-identical twins, where one of each of the twins in each pair had served time in prison. Lange found that 10 of the identical twins but only 2 of the non-identical twins had a co-twin in prison.

  -        This suggests that identical twins (who share more genes than DZ twins) are more likely to both go to prison, showing that there could be a genetic component similar in criminals.
• Twin study by Rain (1993)

  -        Additionally, Raine (1993) reviewed research on delinquent behaviour of twins and found a 52% concordance for MZ twins and 21% for DZ twins.

  -        However, the issue here is that if criminality was purely genetic then the concordance rate would be 100% for MZ twins, suggesting that there is an environmental component as well.
• Kray twins

  -        Notorious London gangsters, boxers when young and violence runs in the family (grandad and older brother boxers).
• Candidate genes

  One gene seems to be associated with violent crime:

  -        Low levels of the MAOA gene – MAOA gene is responsible for production of monoamine oxidase A.

  -        This breaks down neurotransmitters in the brain (e.g. serotonin, dopamine and noradrenaline). Low levels of MAOA have been linked to aggression and impulsive behaviour.
• Mobley case and the MAOA gene

  -        Mobley’s statement that he should not be held responsible due to having a criminal gene was based on the research of Brunner (1978).

  -        Brunner studied 28 male members of a Dutch family (family study) who had histories of impulsive & violent criminal behaviour such as rape and attempted murder.

  -        They all shared a gene that led to low MAOA levels.
• Moffit et al (1992)

  -        Conducted a longitudinal study on 442 New Zealander males recording which ps had been abused as children and what level of MAOA gene they had.

  -        Abuse + low activity MAOA = 9x more likely to be aggressive.

  -        Suggests there is an environmental and genetic component to aggression – interactionist approach.
• Diathesis stress model – a better explanation?

  -        Diathesis – a predisposition or vulnerability

  o   Inherited predisposition to develop the disorder.

  -        +

  -        Stress – environmental stressors

  o   Prenatal trauma, childhood sexual or physical abuse, family conflict, significant life changes.

  -        Development of the disorder

  o   The stronger the diathesis, the less stress is necessary to produce the disorder.
• -        One limitation is the methodological problems with twin studies of criminality.

  o   Lange’s research was poorly controlled (e.g. judgements of whether twin pairs were MZ or DZ based on appearance not DNA testing.)

  o   Also, most twins are reared in the same environment – so concordance rates may be due to shared learning experiences rather than genetics.

  o   Methodological issues such as confounding variables mean twin studies of criminality may lack internal validity.
• -        One strength is the support for a diathesis-stress model of crime.

  o   Mednick et al. (1984) studied 13,000 Danish adoptees and criminality (operationalised as having at least one court conviction which was checked against police records).

  o   When neither biological nor adoptive parents had convictions, the percentage of adoptees that had a conviction was 13.5%. This rose to 20% when either of the biological parents did, and 24.5% when both adoptive parents and biological parents did.
• -        A final limitation is that these explanations are also biologically determinist.

  o   The notion of a ‘criminal gene’ presents a dilemma. The legal system is based on the premise that criminals have personal and moral responsibility for their crimes.

  o   Only in extreme cases (e.g. diagnosis of mental illness) can someone claim that they were not acting entirely of their own free will.

  o   This raises ethical questions about what society does with people who are suspected of carrying criminal genes and who therefore have limited choice.