genetic factors on aggression

• animal studies

  selective breeding supports a genetic basis of aggression
• twin studies


  -MZ & DZ twins

  -Coccaro et al (1977): 182 MZ & 118 DZ; hostility questionnaire; 50% concordance in MZ; 19% concordance in DZ. More genetic similarity = more aggression. 40% contribution to indirect assault; 28% to verbal assault

  -McGuffin & Gottesman (1985): if one MZ was aggressive the other is 87% likely to be too; if one DZ was aggressive the other is 72% likely to be

  -AO3: not just genes, not 100% concordance
• adoption studies


  -Rhee & Worldman (2002): meta-analysis, found a similarity between adoptive children and their biological parent, genetics influence 41% variation in aggression

  -AO3: an interplay with nurture, not just genes
• MAOA gene (1)


  -warrior gene

  -high activity & involved in breaking down serotonin, dopamine & noradrenaline

  -linked to fight or flight

  -low activity MAOA = less MAOA in system, less to break down the neurotransmitters, increases the presence of them in the brain

  -Caspi et al (2002): longitudinal study over 1k male ppts followed from 3 -26. Maltreatment (changes chemicals in brain) is a predictor of aggression, MAOA isn't but is alongside maltreatment

  -Bruner et al (1993): dutch family males = aggressive over generations found to be a faulty MAOA gene and more serotonin

  -Cases et al (1995): disabled MAOA gene in male X chromosome (mice) increasing aggression
• MAOA gene (2)


  low activity MAOA gene cannot counteract changes in neurotransmitters, children with low activity MAOA gene are more anti-social (in adulthood)

  -located in X chromosome

  -Mertins et al 2011: men with MAOA-L (low) were less co-operative in a game than MAOA-H (high) until told that others were being co-operative, they then became less aggressive. Shows that MAOA-L can control their behaviour and may not be the full cause of aggression
• serotonin on aggression


  -serotonin has a regulatory effect

  -when serotonin in the orbitofrontal cortex is optimal, people have self-control

  -low serotonin means there is no reduction of firing neurons in the OFC so less self-control & more aggression
• genetic factors on aggression - AO3


  Strength(s):

  -twin & adoption studies used help reduce extraneous variables. D: still extraneous variables. D: concordance rates were not fully 100% so can't just be genes

  
  

  Weakness(es):

  -biological determinism - based on only genes when nurture also impacts aggression. Ignores free will so is not a full explanation

  -Evidence to suggest a diathesis-stress model. Moffit et al conducted a longitudinal study and found males that were abused = MAOA-L and were 9x more likely to be aggressive. There is an external trigger for aggression which is related to biology. Genes are not the only cause of aggression