Genetic explanations

• Lange (1930) investigated 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.
• Raine (1993) reviewed research on delinquent behaviour of twins and found a 52% concordance for MZ twins and 21% for DZ twins. 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.

  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.
• The Kray twins are notorious London gangsters, boxers when young and violence runs in the family (grandad and older brother boxers).
• 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 gene 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’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.
• 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. They all shared a gene that led to low MAOA levels.
• Abuse + low activity MAOA = 9x more likely to be aggressive.
• -        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.

  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).

  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. This suggests that both genetic inheritance and environment influence criminality – supports diathesis stress.
• -        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.