2.1 Genetic Theories of Criminality

• Concordance Rates


  - means the liklihood of the other twin showing the behaviour if their identical twin shows this behaviour

  - if this is high, it suggests behaviour is caused by genes

  - if concordance rates are higher in identical twins, then behaviour is caused by genetics. if they are higher in non identical twins, it is caused by the environment
• Tshikawa and Raine


  - found a concordance rate of 44% for monozygotic (identical twins) and 21.6 for dizygotic (non identical)
• Christiansen (1977)


  - studied 3586 twins in denmark and found a 35% concordance rate for male monozygotic and 13% for male DZ

  - 21% for female MZ and 8% fir female concordance
• Which suggests that.....


  - you are more likely to be a criminal if your identical twin is one

  - suggests genetics are the cause

  HOWEVER

  since concordance rates are not 100, it suggests genetics are only a contributing factor to crime but is not the only cause and theory of crime
• Crowe (1972) adoption studies


  - compared group of adopted children whose biological mother had a criminal record to a control group, whose parents had no criminal record

  - found that biological mum group, 50% of the children went on to get criminal records by age 18

  - in the control group, only 5% had a record
• Hutchins and Mednick (1975) - adoption 


  - carried out an experiment and found if both biological and adoptive fathers had a criminal record, 36.2% kids became criminals.

  - when only biological parent had a criminal record, 21.4% became criminals (bio)

  - and 11.5% had record when adoptive parent had a record (environment)

  - this can be compared to the control group, where no one parent had a record, and 10.5% went on to get records
• Which show....


  - biology is a bigger contributing factor than environment but isn't the only explanation for criminality
• XYY STUDY


  - suggests inheritance of an extra y chromosome as a male can lead to criminality

  - xyy males tend to be tall and well built, making it easier to offend with a low intelligence

  - Jacob et al believed they were more likely to be aggressive and violent than other males

  - studies suggest xyy males are over represented in prison population with an estimate of 15 in 1000 prisoners being xyy

  - Price and Whatmore found them to be immature and unstable with a tendency to commit motiveless property crime - 1 in 1000 are born with xyy
• STRENGTHS - twin


  - evidence to support it such as the increased concordance rates found in studies by psychologists ie christiansen. This shows the theory has some evidence
• WEAKNESSES - twin


  - twin studies have small sample sizes as its rare to find criminals that are also identical twins. This means that results could be anomolous and cant be generalised which could imapact validity.

  - despite studies shwing increased concordance rates, they are never 100% which suggests genetics are not the only cause of criminality, for example similarities could occur due to shared environment not genes
• STRENGTHS - adoption


  - studies concluded that there is a correlation between adopted children and their bilogical parents
• WEAKNESSES - adoption

  - some children are not dopted immediately after birth and may spend time with their bio parents prior to adoption meaning they may show similarities to them, this is known as the contamination effect

  - they can have small samples, if samples are small it is hard to make generalisations
• STRENGTHS - XYY


  - jacobs found evidence to support it -- more men in prison with xyy than in general population

  - adler et al 2007 indicated that is possible that violence and agression is partly determined by genetic factors which makes the theory more reliable
• WEAKNESSES - XYY


  - this theory only applies to males so doesnt explain all of criminality

  - Theilgard compared xy and xyy nd found agression was not specifically linked to xyy men

  - ignores xyy males who do not commit violent crime and how they avoid this

  - xyy males are overrepresented and this may be explained as they are less intelligent and more likely to be caughtxyy males tend to look more criminal and taller which may lead to a self fulfilling prohecy. they may be labbeled as criminal and live up to this title. the courts may also be harsher when punishing them due to their appearance