genetic factors in aggression

• In twin studies; identical twins are compared between non-identical twins for levels of aggression between them. This is because identical twins share the exact genetic makeup as each other while non-identical share only up to 50%. If identical twins have more similar levels of aggression then it is thought to be due to genetics.
• McGuffin et al found that when studying sets of identical and non-identical twins; Identical twins aggression levels correlated more highly at 87% compared to non-identical twins that correlated at 72%. On first glance this appears to support the basis of genetics being behind such similarities as aggression is shared more closely with twins with identical genetics suggesting shared genes may be responsible.However, non-identical twins also had high levels of similarity in aggression levels, this could be argued to be due to the environment and learning similar aggressive behaviour.
• Adoption Studies have looked at examining levels of aggression between adopted children and that of their biological parents. If a positive correlation is found between adopted children and their biological parents then a genetic effect is implied. If a positive correlation is found between the adopted children and their rearing family; an environmental effect is implied suggesting aggression may be due to learning and not biologically caused.
• Hutchings et al (1975) conducted a huge study reviewing 14’000 danish children who had been adopted. They found a significant positive correlation between the number of convictions for criminal violence among the biological parents and that of their children who had been adopted. This appears to add weight to the argument that genetics is behind aggression and that genes predisposing such may have been passed onto their children.
• role of MAOA 


  MAOA regulates the metabolism of serotonin in the brain and low levels of serotonin are associated with impulsive and aggressive behaviour. Dutch study found that males behaved in a violent and aggressive manner. these men had low levels of MAOA in their bodies
• MAOA-H and MAOA-L


  researchers discovered a variant of the gene associated with high levels of MAOA-H and low levels of MAOA-L
• MAOA gene influences levels of serotonin