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Genetic Theories of Criminality - Coggle Diagram
Genetic Theories of Criminality
Twin Studies
Non-Identical: Dizygotic (DZ) - born at same time but come from 2 separate eggs & share 50% DNA
Identical: Monozygotic (MZ) - born at same time come from one egg & share 100% of DNA
Concordance Rate: probability that if one twin has a characteristic the other twin will have that characteristic
MZ concordance rate should be higher than DZ for genetics to play a role
Lange (1929)
Found MZ twins showed a much higher concordance rate than DZ twins for criminal behaviour. 10/13 MZ twins had both served time in prison compared to 2/17 DZ twins
Ishikawa & Raine
Found a 44% concordance rate for identical twins but only 21.6% for non-identica'
Key Idea
Crime has a genetic cause. MZ twins are genetically identical so if one is criminal the other should be too
Evaluation
Strengths
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 & Raine found a higher concordance rate for MZ & DZ
Weaknesses
If genes were the only cause of criminality MZ twins would show 100% concordance rate, but studies have shown around half/less
Higher concordance rates between MZ may be due to sharing the same home/school etc. (shared environments might cause similarities in their criminal behaviour not identical genes Nature vs. Nurture)
Parents treat MZ twins more alike that DZ -> MZ may feel closer than DZ so one twin may be influenced by the others' criminality to become a criminal too
The Kray Twins
Ronald & Reginal Kray were English organised crime figures in the 1960s
Reginald murdered John McVitie whilst Ronald reportedly held him down whilst his brother was stabbing him the body was never found
Ronald shot & murdered George Cornell in front of a witness but was released as the witness could not identify him
Both arrested & convicted of murder & sentenced to life in May 1968
Adoption Studies
Show whether the genetic/environment shows a stronger effect on a child’s behaviour.
If (in criminal behaviour) the child is more like the biological parents than the adoptive we can suggest a genetic basis for criminality and vice versa.
Key Idea
Comparing adopted children’s level of criminality & their adoptive parents may allow us to see how far genes influence criminality
Evaluation
Strengths
Research design is logical as it allows us to see the importance of nature vs. nurture
Findings of studies give some support to genetic explanations. They show adoptees were more likely to have criminal records of their biological parents have records
Overcomes problems faced by twin studies, whereby identical twins are brought up in the same household which makes it impossible to separate the nature vs nurture debate
Weaknesses
Gottredson & Hirschi argue adoption studies show genes have little effect on criminality
Many children are not adopted immediately after birth but remain with biological parents for some time. The early environment may be a true cause of their criminality.
Adopted children are often placed in environments that are similar to those of their birth family, families of the same class & ethnicity in same location. Similar environments may produce similar behaviours
Aileen Wuornos
Convicted for murdering 6 men in Florida in 1989 & 1990
Mothers parents legally adopted her & her brother -> biological father was imprisoned for child rape & died by suicide whilst in custody
Made her living as a sex worker on Florida's highways
XYY Theory
A chromosome abnormality means that you can be born with an X & two Y chromosomes (XYY) (Supermale)
Jacobs et al (1965)
Suggested XYY's are more aggressive than XY's -> research found 9/315 patients that were XYY's in a max security hospital in Scotland -> over representation of XYY pop. in criminal behaviour
Other studies found 15/1000 prisoners to be XYY when the frequency in the genera; pop. is 1/1000
Key Idea
some males have an extra Y chromosome which may cause violent behaviour
Evaluation
Strengths
Jacobs et al found an associations between XYY and offenders imprisoned for violent behaviour
Price & Whatmore found some links between the syndrome and priority crime
Weaknesses
Even if some violent offenders do have XYY syndrome it does no mean that this is the cause of their violence
The syndrome is very rare (1/1000) so it cannot explains crime
XYY may be overrepresented in prison due to the often having low intelligence so they are more likely to be caught (skewed data)
John Wayne Gacy
American Serial Killer & Sex Offender
Had the XYY chromosome abnormality
Described as sociable & outgoing
Killer Clown
Arrested Dec 1978