AC 2.1 & 3.2 Biological- Genetic Flashcards
What are the genetic theories under biological?
XYY THEORY
Twin studies
Adoption studies
What is Jacob’s XYY theory?
Key idea - some men have an extra Y chromosome (XYY), which was once believed to make them more aggressive and more likely to commit crimes
What is supermale syndrome?
The idea that men with an extra Y chromosome are more aggressive
What is genetic predisposition?
Suggests that some people may be biologically more likely to engage in criminal behaviour
What is the research for Jacob’s XYY theory?
Jacob et al. Found that XYY men are over-represented in prison. 15 in 1000 men have the condition in prison - compared to 1 in 1000 in the general population.
John Wayne Gacy may have had XXY syndrome. He sexually assaulted, tortured and murdered at least 33 men in the USA.
Jacob’s XYY study - EVALUATION
STRENGTHS
- There has been supporting evidence for the theory
Jacob’s et al. Found an association between XYY syndrome and offenders imprisoned for violent behaviour
- Price and Whatmore found some links between the syndrome and property crime
WEAKNESSES
- studies found that genetic abnormalities are widespread throughout the general population
It doesn’t prove the cause of violence from violent offences
- the theory focuses too heavily on genetics
XYY males are over-represented in samples drawn from prisoners and this overstates the importance of the syndrome as a possible cause of crime - although there has been supporting evidence, there has also been evidence that refuses the explanation
Syndrome is very rare (1 in 1000 men have it), so cannot explain much crime.
What are the twin studies?
Key idea - identical twins share 100% of their genes, while non-identical twins share only 50%. If identical twins show more similarity in criminal behaviour than non-identical twins, it suggests a genetic influence on crime.
Theory behind the ‘criminal gene’
Nature VS nurture debate - questions whether genetics (nature) or environment (nurture) has a greater effect on criminal behaviour than
What are monozygotic twins (MZ)?
Key idea - identical twins share 100% of their genes, while non-identical twins share only 50%. If identical twins show more similarity in criminal behaviour than non-identical twins, it suggests a genetic influence on crime.
Theory behind the ‘criminal gene’
Nature VS nurture debate - questions whether genetics (nature) or environment (nurture) has a greater effect on criminal behaviour
What are dizygotic twins (DZ)?
Dizygotic twins are non-identical twins, sharing genes
Born at the same time but come from two separate eggs and share 50% of the DNA (fraternal twins)
What are concordance rates?
The probability (as a percentage) that if one twin has a characteristic the other twin will have the characteristic
What is the research for twin studies?
Johannes Langes
- investigated 13 MZ twins and 17 DZ twins
- found that 10/13 MZ twins had both served time in prison
- only 2/17 DZ twins had both served time in prison
Christensen
- investigated 3586 twin pairs born in Denmark between 1881 and 1910
- 52% concordance rate between MZ twins (if one twin was criminal there was a 52% chance that the other twin was also criminal)
- non-identical twins (Dizygotic) there was only a 22% chance
The research suggests that there is a genetic link between crime and criminal behaviour as there was a higher concordance rate for identical twins, compared to non-identical twins
Twin studies - EVALUATION
STRENGTHS
-Twin studies are natural experiments, as the biological relationships between the twins a naturally occurring variable
Because MZ twins are genetically identical, it is logical to examine whether their offending behaviour is also identical
- Twin studies give some support to genetic explanations. Ishikawa and Raine found a higher concordance rate for identical tins than for non-identical twins
WEAKNESSES
- early twin studies were not controlled and due to this lacked validity
If genes were the only cause of criminality, identical twins would show 100% concordance rate, but studies only show around half or less
-another weakness of twin studies is that the samples used are usually quite small
Impossible to isolate and measure the effect of genes separately from environmental effects
What are adoption studies?
Key idea - compares adopted children’s criminal behaviour with their biological and adoptive parents to see whether crime is inherited or learned
Adopted children do not grow up in the same environment as their biological birth parents and so researchers can see whether genetics or environment has more of an effect n crime and criminal behaviour
Researchers have used adoption studies to test for a genetic cause of crime
What is the research for adoption studies?
- Mednick et al examined data on over 14000 adopted sons in Denmark from 1924-1947. They found that sons were more likely to have a criminal record if a birth parents also had a criminal record (concordance rate 20%). They found that a smaller percentage (14.7%) has a record if their adoptive parents also had one.
Hutchins 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.
Adoption studies - EVALUATION
STRENGTHS
- dotted children are exposed to a different environment to their biological parent to separate out of the influence of genes.
- the research design is logical in theory it allows us to see the relative importance of ‘nature’ (biological parents) VS nurture (adoptive family)
- Findings of adoption studies give some support to genetic explanations. They show adoptees were more likely to have criminal records if their biological agents had criminal records
WEAKNESSES
- the age of adoption may mean that children have already been influenced y their birth parents Gotfredson and Hirschi argue that adoption studies show genes have little effect on criminality
- similar environments may produce similar behaviour
