genetic theories of criminality

• twin studies:

  monozygotic twins are 100% genetically identical.

  dizygotic twins are 50% genetically identical

  If criminality is genetic, both monozygotic twins should be criminal.

  If criminality is genetic, you would expect more identical twins to be criminal than non-identical.
• Adoption studies:

  Adopted children share the same environment as their adoptive parents.

  Adopted children share the same genetics with their biological parents.

  opportunity to investigate nature and nurture.

  If they are similar to their adoptive parents, then criminality is learnt.

  If they are similar to their biological parents, then criminality is inherited through genetics.
• Jacob’s XYY chromosome:

  role of sex hormones in crime.

  24 pairs of chromosomes, last pair being sex chromosomes.

  Males = XY Females = XX

  An abnormality can occur called the ‘super male syndrome’ (XYY)

  A male with this is more likely to be more aggressive and violent and have lower intelligence =.

  A higher-than-average number of men in prisons for violent crimes have been found to have the XYY chromosome variant.
• strengths of twin studies?

  -Christianson studied 3,586 twin pairs in Denmark, 52% of monozygotic twins were concordant, in contrast to 22% of dizygotic twins (genetics must play a role, shared genetics in identical pairs mean both are likely to turn to crime)
• weaknesses of twin studies?

  -role of genetic questioned as concordance rates are never 100%, likely genetics only plays a part in criminality rather than causing criminality

  -hard to separate the effects of nature and nurture, twins share genetic informations and are likely to share experiences (meaning it is not possible to identify which influences behaviour more which leads to both twins committing crime)
• strength of adoption studies?

  -mednick researched data on 14,000 adopted boys, 20% risk of criminality if the boys had biological parents who had committed crime, 14.7% risk if the boys had adoptive parents that had committed crime (suggests that crime is more likely if you are genetically related to someone who commits crime)

  -good way to separated the effects of nature and nurture, adopted children grow up away from their biological parents, possible to investigate the influence of genetics without the influence of exposure to criminal behaviours
• weaknesses of adoption studies?

  -not entirely possible to separate the effects of nature and nurture, someone who is adopted at 3 years old could have long-time effect from early experiences with their biological parents

  -possible that adoptive parents not too dissimilar to biological parents since children are often placed in similar families (e.g. location, background), life of adopted child may be similar to life child would have had with biological parents
• strengths of XYY syndrome?

  -research evidence that supports, Price and Whitemore found XYY males were unstable and likely to commit motiveless crimes, suggests the lower intelligence of people with XY syndrome may be a factor that influences their criminality
• weaknesses of XYY syndrome?

  -XYY syndrome is rare, occurring in 1 in 1000 males, despite this crime rates involving male are not rare, meaning XYY is not a common cause of crime, other explanations need to be considered.

  -though XYY pattern is found in some violent offenders, it is not possible to determine whether the XYY pattern caused them to commit the crime, other factors like moral upbringing, socio-economic factors could have influenced their behaviour