2.1 biological theories

• Criminological theories


  Theories about the causes of crime, can be grouped into three main types: biological, individualistic and sociological
• Biological theories of criminality

  1. Criminals are biologically different from non-criminals and this difference causes them to commit crime

  2. Physiological theories focusing on criminals' physical characteristics

  3. Genetic theories that see criminality as inherited

  4. Brain injuries and disorders that cause people to offend

  5. Biochemical explanations involving factors such as hormones in offending
• Physiological theories


  Claim that the physical features of criminals differ from those of non-criminals
• Lombroso's theory of 'born criminals'

  • Criminals were physically different from non-criminals and could be identified by their distinctive physical features
  • Criminals were atavistic, throwbacks to an earlier, primitive stage of evolution
• Sheldon's somatotypes theory


  • Certain body types or 'somatotypes' are linked to criminal behaviour
  • Mesomorphs are the somatotype most likely to engage in crime
• Genetic theories


  Criminality is inherited and passed down from parent to child
• Twin studies


  • Identical twins share the same genes, so if one twin is criminal, the other twin ought to be criminal too
  • Adoption studies compare adopted children's behaviour to their biological birth parents and adoptive parents
• XYY syndrome


  An abnormality where a person has an extra Y (male) chromosome, which has been linked to aggression and potential violence
• Brain injuries and disorders

  Certain diseases, lesions and functions of the brain have been linked to criminal behaviour
• Biochemical explanations


  Biochemical substances and processes, such as sex hormones, blood sugar levels and substance abuse, can affect brain chemistry and mental processes, leading to criminal behaviour
• Substances linked to criminal behaviour

  • Alcohol
  • Cocaine and 'crack'
  • Cannabis, heroin and MDMA
  • Lead and synthetic food colouring
  • Vitamin B deficiency
• Adoption studies


  Studies that compare adopted children to their biological birth parents and to their adopted parents to test for a genetic cause of crime
• The thinking behind adoption studies is that an adopted child (especially if adopted soon after birth) shares the same environment as their adoptive parents, but the same genes as their biological parents
• If the adoptee's behaviour in regard to criminality is more similar to their birth parents' behaviour


  This would support a genetic explanation
• Mednick et al examined data on over 14,000 adopted sons in Denmark from 1924 to 1947
• They found that sons were more likely to have a criminal record if a birth parent also had a record (a concordance rate of 20%)
• They found that a smaller proportion (14.7%) had a criminal record if their adoptive parent had one
• Hutchings and Mednick compared adoptees with and without criminal records
• They found that adoptees with criminal records were more likely to have biological parents with criminal records than adoptees whose birth parents did not have criminal records