Genetic Explanations For aggression

• MAOA Gene(|)

  Controls the production of enzymes that break down serotonin.

  There are two alleles of this gene.

  -> Shorter allele which produces less enzyme but produces more aggressive people.

  -> Longer allele which produces more enzymes but produces less aggressive people.

  
  

  Explanation) You need just the RIGHT amount of serotonin to increase/decrease aggressive behavior.
• MAOA Gene (||)


  Not all people with the gene mutation exhibit aggressive behavior, and environmental factors, such as childhood abuse, can also contribute to the likelihood of aggressive behavior.

  -> Highlights the interaction between nature & nurture in determining behavior.
• Variations of MAOA Gene


  Low-activity variant) This leads to enzyme deficiency (producing less enzyme), associated with higher levels of aggression due to an imbalance of neurotransmitters.

  
  

  High-activity variant) Produces more enzymes, leading to more breakdown of serotonin, and is associated with lower aggression
• Study MAOA-L variant


  Brunner Studied 28 males from a Dutch family with a history of impulsive, aggressive, and criminal behavior.

  -> Found abnormally low levels of the enzyme MAO-A and the MAOA - L gene variant.

  -> Highlights genetic influence on aggression but emphasizes interaction with environmental factors.
• Twin Studies

  Rhee and Waldman (2002) analyzed 51 studies of twins and adoptions and found that 40% of anti-social and aggressive behavior is influenced by genetics, while 60% is influenced by the environment. This highlights that both genetic predisposition and environmental factors contribute to shaping aggressive behavior.
• XYY Gentotype

  The XYY genotype is a genetic variation where a male has an extra Y chromosome, making them XYY instead of the typical 46 chromosomes (23 pairs). Males with this genotype tend to be taller than average, have a low IQ, and have behavioral issues.

  
  

  In 1966, Price et al. found that 28% of male patients in hospitals for the criminally insane had the XYY genotype, compared to only 0.1% in the general population. This suggests a potential link between the XYY genotype and aggressive behaviour.
• Strength - Link between MAOA Gene and Aggression

  Vanessa Mertins et al. (2011) studied male participants with different forms of the MAOA gene (low-activity and high-activity) in a money distribution game. They found that men with the high-activity form (MAOA-H) were more cooperative and less aggressive than those with the low-activity form, supporting a link between MAOA gene activity and aggressive behavior.
• Limitation - The mechanism linking MAOA and Serotonin is unclear

  Research links low serotonin levels to aggression. However, people with the low-activity form of the MAOA gene (MAOA-L) should have higher serotonin, as low MAOA activity leads to less breakdown of serotonin. Despite this, they tend to be more aggressive, meaning the relationship between MAOA, serotonin, and aggression is not fully understood.