2. Genetic factors

• Twin studies - AO1

  - Several twin studies have suggested that heritability - - genetic factors account for 50% of the variance in aggressive behaviour
• Emil Cooccaro et al (1997) - procedure - AO1


  - Studies adult male MZ and DZ twins

  - Because MZ share 100% DNA but DZ share 50%. There would be greater similarities in aggressive behaviour between MZ twins if aggression is mostly influenced by genetic factors
• Emil Cooccaro et al (1997) - Findings - AO1


  - Aggressive behaviour defined as direct physical assault - researchers found concordance rates of 50% for MZ twins and 19% for DZ

  - Veral aggression - 28% for MZ and 7% for DZ
• Adoption studies - AO1

  - Similarities in aggressive behaviour between adopted child and their biological parents suggest that genetic influences are operating

  - Similarities with adopted parents suggest environmental influences are operating
• Rhee and Irwin Waldman (2002) - procedure - AO1


  - Meta-analysis of adoption studies of direct aggression and antisocial behaviour

  - Anti-social behaviour was a prominent feature of aggressive behaviour
• Rhee and Irwin Waldman (2002) - findings - AO1

  - Genetic influences accounted for 41% of variance in aggression

  Pretty in line with twin studies
• The MAOA gene - AO1

  - The gene responsible for the activity of the enzyme monoamine oxidase (MAOA) in the brain.

  - The low-activity variant of the gene is closely associated with aggressive behaviour.
• The MAOA enzyme role - AO1

  - Role is to mop up neurotransmitters in the brain after nerve impulse has been transmitted from one neurone to another

  - Breaks down steroin into chemicals that are recycled or excreted - process known as catabolism

  The production of this enzyme is determined by the MAOA gene
• Dysfunction in MAOA gene - AO1

  - leads to abnormal activity in MAOA enzyme

  - Affects levels of serotonin in the brain

  - One variant of MAOA gene - nicknamed warrior gene - leads to low activity in areas of the brain and has been associated with various forms of aggressive behaviour
• Han Brunner et al (1993) - procedure - AO1


  - Studied 28 male members of large Dutch family

  - who were reported to be involved in numerous aggressive and violent criminal behaviour e.g. rape, physical assault and attempted murder
• Han Brunner et al (1993) - Findings - AO1


  - Researchers found that these men had abnormally low levels of MAOA in their brains - and the low-activity version of MAOAO gene
• Gregory Stuart et al (2014) - Procedure - AO1


  - Studied 97 men

  - been involved in inflicting intimate partner violence (IPV)

  - part of a batter treatment programme
• Gregory Stuart et al (2014) - findings - AO1


  - Men with low-activity MAOA gene were most violent predators of IPV

  - engaged in highest levels of physical and psychological aggression

  - Inflicted worst injuries on partners
• Gene-environment (GxE) interactions


  - Genes are crucial influences on aggressive behaviour, but they don't function in isolation

  - Low activity of MAOA gene is only related adult aggression when combined with early traumatic life events
• Giovanni Frazzetto et al (2007) - Findings - AO1


  - Found an association between higher levels of antisocial aggression and the low-activity MAOA gene variant in adult males

  - This was only the case for those who had experienced a significant trauma

  - sexual or physical abuse during the first 15-years of their lives

  - Those who had not expericnes such trauma did not have high levels of adult aggression even if they posseed low-activity MAOA variant.

  - Stong evidence of gene-environment interaction - diathesis-stress
• Multiple genetic influences - 🙁

  P - There may be several genetic influences on aggression

  E - Stuart et al found that IPV in men was associated with low-activity MAOA gene but also with the steroid transporter gene (5-HTT) another gene that influences serotonin activity in the brain

  A - This has made looking for other influencing genes is a very active current research area. Vassos et al (2014) - meta-analysis found no evidence of an association between one single gene and aggression

  L - It may be that multiple genes are responsible for such a multifaceted behaviour as aggression
• Measuring aggression - 🙁


  P - Furthermore, methods of measuring aggression differ between studies

  E - May range from self-reports, parent and teacher reports and direct observation

  A - Rhee and Waldman's did a meta-analysis of 51 twin and adoption studies. Genetic factors had a greater influence on aggression in studies using self-reports rather than parent or teacher reports Show that research findings vary depending on how aggression is measured

  L - Becomes difficult to draw valid conclusions about the role of genetic factors
• Research support for the role of the MAOA gene - 😊

  P -Research support for the role of MAOA gene in pro-social behaviour

  L - If Low-activity MAOA gene leads to greater aggression then high-activity MAOA gene must lead to more prosocial and less aggressive behaviour

  A - Mertins et al (2011) - studied participants with low-activity and high activity variants of MAOA gene in a money-distributing game Males with high-activity MAOA variant were more co-operative and made fewer aggressive moves than low-activity participants

  L - Findings confirm the importance of MAOA gene in aggressive behaviour
• Insolating genetic factors - 🙁


  P - One limitation is that it's challenging to establish how influential genes are in aggressive behaviour

  E - It's difficult for researchers to separate genetic and environmental factors. An individual may possess a gene associated with aggression, but behaviour is only expressed in environmental conditions are favourable.

  A - McDermont et al (2009) showed that participants with low-activity MAOA gene behaved aggressively in lab based money allocation game but ONLY when provoked

  L - It can be hard to understand the genetic factors which influence aggression