Jacobs XXY Theory

• How are "super males" different from "normal males"?

  Super males are typically more aggressive and more likely to be violent compared to regular males- Jacob et al suggested that XXY men are over-represented in the prison population.
• How many people have the XYY chromosome pattern in the UK?

  Around 25,000- 1 in every 1,000 boys have it
• Other than aggression and violence, what are other characteristics of an XYY pattern?

  Might be taller, have problems with spoken language and processing spoken words, coordination problems, weaker muscles and hand tremors and typically have higher rates of ADHD
• Who was John Wayne Gacy (who was thought to have the XXY gene) and what was his crimes?

  • He was a serial killer and killed 33 boys and young men
  • Had a tendancy to be a sadist
  • Sexually assaulted a boy in 1968 and again after being released on parole in 1970
  • 29 bodies were discovered in his house and another 3 in a river
• Evaluating XYY theory- What are the strengths/positives of this theory?

  
  

  Positives- Research by Jacob at al found a significant number of men in prison had XYY chromosomes instead of the normal XY. Adler et al found that it is possible that aggression and violent behaviour is partly determined by genetic factors.
• Evaluating XYY theory- what are the weaknesses/limitations of this theory?

  Negatives- Theilgaard's research the traits of XYY men compared to XY men, he found that aggression was not amoung XYY men only. This theory focusses too heavily on genetic and ignores environmental causes of someone's behaviour. For example, John Wayne Gacy not only had an XYY chromosome, but also had a difficult relationship with his father and got sexually assaulted by a family friend.