E2a1 Theilgaard (1984): the criminal gene

Question 1

Aim of Theilgaard’s study

Answer 1

Theilgaard wanted to see if criminals ad a particular gene that could be responsible for criminal behavior

Question 2

Procedure of Theilgaard’s study

Answer 2

1) took blood samples from over 30,000 men
2) From these, 2 chromosome abnormalities found: XXY and XYY
3) 16 men had XXY, 12 had XYY
4) men interviewed by social worker about backgrounds and criminal history, given intelligence tests. Personality tests used to see if they displayed more aggression than normal XY males

Question 3

Results of Theilgaard’s study

Answer 3

XYY males had slightly lower levels of intelligence, and tended to be more aggressive- can be evidence fro criminal gene- aggression is a sign for crime. There were way more similarities than differences between XXY males and XYY males. No solid evidence for criminal gene found

Question 4

Conclusion of Theilgaard’s study

Answer 4

It provides limited evidence for XYY males being more aggressive than XXY males. They were more similar than different

Question 5

Strengths of Theilgaard’s study

Answer 5

1) all tests and interviews with the men conducted by social worker that didn’t know the study aim- prevented researcher bias, would not have led the males to answer a particular way/ interpreted findings to meet their expectations
2) large range of tests used to measure different aspects of the men’s lives, backgrounds and personality.

Question 6

Weaknesses of Theilgaard’s study

Answer 6

1) only a small sample of men used for investigation- cannot be sure all XYY males more aggressive/ have lower intelligence. Findings can’t be generalised to all XYY males.
2) XYY males fairly average, can’t be picked out easily+ abnormality not inherited, can’t be tracked down in families, ^makes first problem worst
3) correlation not causation- might not have caused increased aggression at all, many other reasons: e.g could be due to lower intelligence and delayed speech- made school hard for them, made them frustrated- led to anger and aggression in childhood which became a pattern in adulthood
4) not all criminals have XYY, not all XYY males criminals- can’t be sure abnormality causes crime at all
5) Ethical problems- XYY males might become the self-fulfilling prophecy if identified and labelled