AO3

• Genetic Explanations: Problems with Twin Studies

  • Early studies, such as Lange, were poorly controlled and judgements related to Zygosity (whether twins are MZ or DZ) was based on appearance rather than DNA testing, lacking validity.
  • Twin studies usually involve small samples and twins are an unusual sample which is not representative of the population.
  • Most twins are reared in the same environment which is a cofounding variable as concordance rates may be due to shared learning experiences rather than genetics.
• Genetic and Neural Explanations: Evaluation Points

  • Problems with twin studies
  • Genetic research support: Medrick
  • Neural research: Kandel and Freed
• Genetic and Neural Explanations: Genetic research

  In 1974, Mendrick conducted a study of 13,000 danish adoptees. He found that 13.5% of adoptees had a criminal conviction when neither of their biological or adoptive parents did, 20% of adoptees had a criminal conviction when either their biological or adoptive parents did and 24.5% of adoptees had a criminal conviction when both their biological and adoptive parents did. This shows the influence of genetic and environmental factors in offending behaviour, as suggested by the diathesis-stress model.
• Genetic and Neural Explanations: Neural research

  Kandel and Freed (1989) studied the link between the frontal lobe and crime. They reviewed evidence of frontal lobe damage, including the prefrontal cortex, and antisocial behaviour. Those with frontal lobe damage tended to show emotional instability, impulsivity and inability to learn from their mistakes. The frontal lobe is responsible for planning behaviour. This supports the frontal lobe and prefrontal cortex as an explanation of offending.