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Summary Criminology Unit 2 AC2.1
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Notes for Unit 2 AC2.1 Describe biological theories of criminality Criminology WJEC
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AC2.1 Describe biological theories of criminalityKey Terms
Monozygotic - Identical twins
Dizygotic - Non-identical (fraternal) twins
Concordance - In agreement or harmony
Atavistic - Relating to something ancient or ancestral
Somatotype - Body shape
Genetic Theories
Genetic theories as an explanation for criminal behaviour emerged with modern criminology
in the 1700s
In recent times there has been an increase in research on the genetics of behaviour,
including anti-social behaviour
XYY theory
➔ Theory of criminality
◆ Suggests that some crime might be attributable to a chromosome abnormality
➔ Chromosomes are structures in cell nuclei
◆ Humans usually have 46 chromosomes
● 44 of which determine the shape and constitution of out body
● Two determine sex
➔ Sex is determined by the pattern of a person's sex chromosomes
◆ XX in a woman
◆ XY in a man
● It is a Y chromosome that makes a person male
➔ There are a variety of chromosome abnormalities
◆ Some of which involve the presence of extra chromosomes
◆ One such condition, known as ‘XYY’, involves the presence of an extra Y
chromosome
● XYY men, sometimes called super males, have been of interest to
criminologists because of the suggestion that they are more
aggressive and more inclined to be violent than males with a single Y
chromosome
➔ Jacob et al. (1965) suggested that men with the XYY syndrome were more
aggressive than normal ‘XY’ men
➔ There are also some studies that suggest XYY men are over-represented in the
prison population
◆ There are 15 sufferers per 1000 in prisons and one per 1000 in the general
population
➔ The serial killer John Wayne Gacy is said to have XYY syndrome
◆ He sexually assaulted, tortured and killed at least 33 men in the USA
Positives
, ● Clear association found by Jacob et al between XYY syndrome and violent offenders
● Supporting evidence by Price & whatmore
Negatives
● Even if violent offenders have XYY syndrome, there is no proof it is the cause off
their behaviour
● XYY males are tall and well- built so they fit the stereotype of a 'violent offender' and
may begin to live up to their label - self fulfilling prophecy
● There may be more XYY prisoners because they are said to have low intelligence so
are more likely to be caught - therefore, it's not an actual cause of criminality
● The syndrome is rare (1 in 1,000 men have it) so it cannot explain much of the crime
that happens
● It cannot explain why women commit violent crimes
● Those in the ward might have other mental illness', the patients may have similar
backgrounds
Twin studies
➔ Look at the impact of genetics on criminality
➔ Support the contention that a heritable trait may increase risk for criminal behaviour
➔ Identical twins are monozygotic (MZ) as they are from one fertilised egg
◆ Such twins share 100% of their DNA,
➔ Dizygotic (DZ) twin are from two separate eggs and share 50% of their DNA
◆ When both of the twins share a characteristic there is said to be a
concordance rate
➔ In order to assess the role of genetic and environmental influences, or the nature
versus nurture debate, various twin studies have taken place
◆ There is some evidence to suggest that genetics or nature may play a role in
criminality to the extent that concordance in MZ twins is greater than that in
DZ twins
➔ One of the earliest twin studies was reported by the German Physician Johannes
Lange (1929)
◆ He found that MZ twins showed a much higher degree of concordance than
DZ twins for criminal behaviour
● Ten of the 13 MZ twins had both served time in prison, whereas only
two of the 17 DZ twins had such concordance
➔ Christiansen (1977) studied 3,586 twin pairs from the Danish islands
◆ Found concordance rates of 35% MZ and 13% DZ for male male twins
◆ 21% MZ and 8% DZ for female twins
Positives
● Logical way to examine biological explanations to criminality as MZ twins are 100%
identical
● Support from twin studies eg. Christiansen's study
Negatives
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