BIOLOGICAL PSYCHOLOGICAL
THEORIES
1. THEILGAARD - 1984
Aim: To determine if criminals have a particular gene that could lead to criminal
behavior
A. Procedure
i. Blood samples taken from 30,000 men born in 1940 and found chromosomal
abnormalities XXY and XYY
ii. 16 men had XXY chromosomes, and 12 men had the XYY chromosomes
iii. The men were interviews by an independent social worker about their
background and criminal records
iv. Personality and intelligence tests were taken
B. Results
i. XYY males had higher levels of aggression and lower intelligence
ii. But sample size means there’s limited evidence to suggest that XYY males are
more aggressive than XXY men
iii. They had more similarities than differences
iv. 1 in 1000 men had XYY chromosomes
C. Strengths
i. Independent social worker eliminated research bias as they had no prior
knowledge of the studies aims
ii. Varity of tests were uses both biological, blood tests, and psychological tests
D. Limitations
i. Not all criminals have XXY or XYY chromosomes and not everyone with XXY
or XYY chromosomes are criminals
ii. Limited number of individuals had the chromosomal abnormalities
iii. Only 1 in 1000 men have the XYY chromosome
iv. Only 12 men who had the XYY chromosome were tested so results cannot be
projected onto the wider public
2. CHRISTIANSEN - 1977
THEORIES
1. THEILGAARD - 1984
Aim: To determine if criminals have a particular gene that could lead to criminal
behavior
A. Procedure
i. Blood samples taken from 30,000 men born in 1940 and found chromosomal
abnormalities XXY and XYY
ii. 16 men had XXY chromosomes, and 12 men had the XYY chromosomes
iii. The men were interviews by an independent social worker about their
background and criminal records
iv. Personality and intelligence tests were taken
B. Results
i. XYY males had higher levels of aggression and lower intelligence
ii. But sample size means there’s limited evidence to suggest that XYY males are
more aggressive than XXY men
iii. They had more similarities than differences
iv. 1 in 1000 men had XYY chromosomes
C. Strengths
i. Independent social worker eliminated research bias as they had no prior
knowledge of the studies aims
ii. Varity of tests were uses both biological, blood tests, and psychological tests
D. Limitations
i. Not all criminals have XXY or XYY chromosomes and not everyone with XXY
or XYY chromosomes are criminals
ii. Limited number of individuals had the chromosomal abnormalities
iii. Only 1 in 1000 men have the XYY chromosome
iv. Only 12 men who had the XYY chromosome were tested so results cannot be
projected onto the wider public
2. CHRISTIANSEN - 1977
