Genetic

• Twin studies state that if one member of a family has criminal genes, it is likely his or her blood relatives will too.
• Identical twins, or monozygotic twins, share exactly the same genes as they developed from the same egg. Non identical (fraternal) twins, also known as dizygotic twins. Early twin studies were flawed for judging the difference between the two twins based on appearance, not genetics.
• Christiansen's study (1977) was conducted on 3586 twin pairs in Denmark. He found a 52% concordance rate between MZ twins. Among DZ twins, there was only a 22% chance.
• A strength of twin studies would be that because MZ twins are genetically identical, it is logical to examine whether their offending behaviour is also identical.
• A second strength of twin studies would be that twin studies give some support to genetic explanations. Ishikawa and Raine found a higher concordance rate for identical than for non-identical twins. (the concordance rates measure the probability of both twins being criminals, if one of them is)
• A limitation of twin studies is that if genes were the only cause of criminality, identical twins would show 100% concordance but studies show only 50% or less. There must be some other factor.
• Another limitation of twin studies would be that higher concordance rates between identical twins may be due to sharing the same home, class etc. Their shared environment might cause similarities in their criminal behaviour, not biological disposition.
• A limitation of twin studies would be that parents treat identical twins more alike than they do non-identical twins. Also, identical twins may feel closer than non-identical twins, so they could potentially influence each other.
• A limitation of twin studies would be that it is impossible to isolate and measure the effect of genes separately from environmental effects.
• A limitation of twin studies would be that in early studies, a lack of knowledge surrounding DNA would have made it impossible to tell the genetics of their participants.
• Adoption studies have been used to explore the genetic origins of crime. Environment is shared with adoptive parents and genes with biological parents.
• Mednick et al examined data on 14,000 adopted sons in Denmark 1924-47. Sons were more likely to have a criminal record if their parents did. 20% concordance rate. A smaller proportion (14.7%) had a criminal record if their adoptive parent had one.
• A strength of adoption studies is that they overcome the problem faced by twin studies - where biologically identical twins are raised in the same household, which makes it impossible to separate genes from environment.
• A strength of adoption studies is that the research design is logical. In theory, it allows us to see the relative importance of 'nature' and 'nurture'.
• A strength of adoption studies is that findings of these studies give some support to genetic explanations. They show adoptees were more likely to have criminal records if their biological parents had criminal records.
• A limitation of adoption studies would be that Gottfredson and Hirschi argue that adoption studies show that genes have little effect on criminality.
• Adopted children are often placed in environments similar to those of their birth family, with families of the same class, ethnicity etc. - similar environments may produce similar behaviour.
• A limitation of adoption studies is that many children are not adopted immediately after birth but stay with their biological family for some time. This early environment may be the true cause of their criminality.
• Jacob et al's XYY theory states that some crime may be attributable to chromosomal abnormality. XX is a woman, XY is a man. XYY is known as super-male syndrome.
• Jacob et al studied imprisoned criminals in psychiatric hospitals. XYY men tend to be tall and well built, and of lower intelligence. Jacob et al claimed they they were more aggressive and potentially violent. XYY men are over represented in the prison population - there are 15 sufferers per 1000 in prisons vs 1 per 1000 in the general population.
• A strength of XYY theory is that Jacobs et al found a correlation between imprisoned violent offenders and this syndrome.
• A strength of Jacobs et al is supporting evidence. Price and Whatmore found a link between XYY syndrome and property crime.
• A limitation of Jacobs et al is that even if some violent offenders have the syndrome, it doesn't necessarily mean that it is the cause.
• A limitation of Jacobs et al is that XYY males are tall and well built, so they fit the stereotype of 'violent offenders' and get labelled as such by the courts, so they are more likely to get a prison sentence. As a result, XYY males are over-represented in samples drawn from the prisoners and this overstates the importance of the syndrome as the cause of crime.
• A limitation of Jacobs et al is that, alternatively, XYY males may be over-represented in prison because they often have low intelligence, meaning they are more likely to be caught. Samples drawn from prisoners are therefore skewed.
• The syndrome is vary rare (only 1 in 1000 men have it) so it cannot explain much crime.
• Genetic theories state that criminality is caused by genetic factors, so eugenicists believe in punishment before an actual act has been committed. Eugenicists are also controversial for believing that the human race is degenerating due to the lower classes 'breeding' with the upper classes.
• Eugenicists believe in compulsory sterilisation. They set up pressure groups to campaign for this legislation, which was introduced in many countries. For example, in 1927, the US Supreme Court ruled that it was compulsory to sterilise the 'unfit'.
• Other forms of eugenicist policy include restrictions on marriage and abortions.
• The most extreme case of eugenic policy was in Nazi Germany. They wanted to 'purify' the 'Aryan master race'. Initially, the mentally and physically disabled were targeted first - with 400,000 sterilised against their will. The Holocaust escalated this, murdering 6 million Jews alone.