genetic influences

• what did twin studies suggest about aggression?

  several studies have suggested that heritability accounts for

  50%of variance in aggressive behaviour.

  MZ twins share 100% of their gene but dizygotic twins are 50%. expect greater similarities in MZ if mostly genetic. both MZ and DZ are raised together but MZ twins have a greater degree of genetic similarity than DZ twins
• What key research is there to twin studies?

  Coccaro et al studied adult male monozygotic and dizygotic twins concordance rates of 50% for MZ and 19% for DZ in physical aggression verbal aggression were 28% for MZ and 7% for DZ
• What can we conclude about the genetic root of aggression from coccaros findings

  Coccaros research suggests a strong genetic link because concordance rates are higher for MZ. remember despite both twins sharing the same environment , the Mz twins share a greater proportion of genes
• What do adoption studies show?

  Similarities is aggression between adopted child and biological parent suggest support for genetic influences are operating. similarites with the adopted parents suggest that environmental influences are operating. Rhee and Waldman carried out a meta-analysis of adoption studies of direct aggression and antisocial behaviour a prominent feature of which is aggressive behaviour. They found genetic influences account for41%of the variance in aggression, which is more or less in line with findings from twin studies.
• What is the MAOA?

  is an enzyme. its role is to mop up neurotransmitters in the brain after a nerve impulse has been transmitted from one neuron to another. it does thisby breaking down the neurotransmitter, serotonin into chemical to be recycled or excreted.A dysfunction in the operation of this gene may lead to abnormal activity of the MAOA enzyme , which effect serotonin levels
• What is a variation of the MAOA gene?


  warrior geneleads to low MAOA activity in areas of the brain and has been associated with various forms of aggressive behaviour.Brunner et al studied 28 male members of a large dutch family who where repeatedly involved in impulsively aggressiveviolent criminal behaviours such as rape, attempted murder and physical assault. The researchers found that these men had abnormallylow levels of MAOA in their brains and the low activity version of the MAOA
• Describe the role of the MAOA gene in aggression and explain how it might be responsible for Adam's aggressive behaviour. 8 marks

  •Serotonin has a calming influence, and lower levels are associated with impulsive and aggressive behaviour.•Monoamine oxidase A (MAOA) is an enzyme that breaks down important neurotransmitters in the brain, including serotonin; low levels of serotonin have been associated with impulsive and aggressive behaviour. MAOA is regulated by the MAOA gene and humans have various forms of the gene, resulting in different levels of activity of the enzyme.•A variant of the MAOA gene (The low MAOA variant – which produces lower levels of monoamine oxidase) is•associated with aggression. The low MAOA variant is much more frequent in populations with a history of warfare.Research has found that those with the low MAOA variant are more likely to grow up and be aggressive, but only if they were maltreated as childrenapplication:•Adam has found out that there is a history of violence in his biological family, not his adoptive family, so this suggests that he might have inherited the low MAOA variant and that this may be responsible for his aggressive behaviour.•It may be that his serotonin levels are lower than normal, so he overreacts to external threats and is unable to control his impulsive and aggressive behaviour leading him to commit violent crimes.•In addition, he was taken into care when he was three years old so may have been maltreated as a child which background, combined with the inherited MAOA gene, has led him to commit violent crimes.
• What is the support by Stuart et al for the MAOA gene

  Studied97 men because they had been involved in inflicting intimate partner violence were part of a betterer treatment programme. Men with low activity MAOA gene were found to be the most violent perpetrators of IPVthey were engaged in the highest levels of physical and psychological aggression inflicted in partners and inflicted the worst injuries on their partners
• what did Frazzeto et al find?

  an association between higher levels of antisocial aggression and the low activity MAOA gene variant in adult male as expectedBut this was only the case in those who had expericenced significant trauma (ie sexual or physical abuse) during the first 15 years of life.Those who had not experienced such childhood trauma did not have particularly high levels of aggression as adult, even if they possessed the low activity MAOA variant. this is strong evidence of a gene- environment interaction (sometimes described as diathesis stress)
• what is the low MAOA activity have to be combined with to be realted to adult agression

  early childhood trauma
• what did mcdermott et al find?

  •Just because a gene is present doesn’t necessarily mean it will be expressed – it will only be expressed if environmental triggers are present.•McDermott et al. (2009)found that in a lab study based on a computer game, that participants with thelow activity MAOA gene were aggressive but only when provoked otherwise they were the same or less aggressive that control participants.
• Why was mcdermott et al critisised?

  reductionist. As well as genetic factors, there are many environmental factors that influence the manifestation of aggressive behaviour.Genetic factors can also influence environmental factors and vice versa in gene-environment interactions. The explanations discussed only focuses on genes, though genes and the environment are intrinsically related: one cannot be fully explained without the other.
• What other gene did stuart et al find is associated with intimate partner violence?

  •the serotonin transported gene (5-HTT), another gene that influences serotonin activity in the brain. It was thecombinationwith MAOA that was most closely linked with IPV.
• What did Vassos et al find?


  meta analysis- not support as could find no evidence of an association between any single gene and aggression.They calculate that hundreds or thousands of genes interact in complex ways to determine aggressive behaviour.
• what is a limitation to genetic explanations?

  it is verydifficult to determine the nature of this relationship as many different genes contribute to aggression in various waysmaking the topic difficult to research effectively.
• how can you measure aggression?

  self-reports,parent and teacher reports, anddirect observations
• Rhee and Waldman (2002) - meta-analysis


  51 twin and adoption studies, genetic factors had a greater influence on aggression in studies using self-reports rather than parents or teacher reports.
• what is a limitation to measuring aggression

  If research findings vary depending on how aggression is measures, it becomes very difficult to draw valid conclusions about the role of genetic factors.
• what is support for the role of a MAOA gene?

  •Mertins et al. (2011)studied participants with low-activity and high-activity variants of the MAOA gene in a money-distributing game.•Participants had to make decisions about whether or not to contribute money for the good of the group. The researchers found that males with thehigh-activity variantwere more co-operative and made fewer aggressive moves than thelow-activity participants.This suggests that MAOA reduces aggression by regulating levels of these neurotransmitters and provides evidence for the link between MAOA and aggression.
• What study by Godar et al show with mice?


  •The hypothesis that the MAOA gene might play a role in human aggression originated inresearch with mice.•Genetic deletion techniques allow researchers to ‘knockout’ single genes, an experimental manipulation that lets them observe subsequent effects on aggression.•For example,Godar et al. (2014)showed that MAOA knockout mice have significantly increased brain serotonin levels and are hyperaggressive.•Furthermore, when serotonin was blocked by the drugfluoxetine, the mice reverted to their non-aggressive behaviour.Godar’s research provides further evidence for the role of MAOA (even more so because fluoxetine also reduces aggression when injected).
• Evaluate Godars study


  based on animal studies which means there is a lack of generalisability to humans. The differences between the nervous system of a mouse and that of a human will be vastly different.

  Therefore, although animal research allows us to establish a link between MAOA and aggression, the validity of the link can be questioned as the findings may not fully apply to complex human nervous systems.
• Counter, issue and debate and evaluate animal studies support for link with MAOA gene and aggression


  However, a noteworthy finding fromFreazzetto et al. (2007)showed high levels of adult aggression to be associated with low-activity MAOA, but this was only expressed when significant life trauma was experienced before the age of 15 (i.e. sexual abuse, neglect etc.). Illustrating that although there are precipitating factors in aggression, there needs to be an environmental trigger for the gene to be expressed.Therefore, it is likely this with such complex and broad topics (such as aggression) that bothnature and nurtureare involved. For this reason, aninteractionist approachwould be a more valuable way to study aggression.Although, genetic explanations do provide insight into the causes of aggression. Only considering genetics isbiologically reductionistas environmental interactions must be taken into account to gain a valid understanding of aggression.