The role of genetic factors on aggression

James Farley
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James Farley
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PSYA3 Psychology AQA - Genetic factors into aggression

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The role of genetic factors on aggression
  1. Twin Studies
    1. McGuffin and Gottesman (1985)
      1. Research provides support for the role of genes in aggression as they found a concordance rate of 87% for aggressive and antisocial behaviour for MZ twins, compared to 72% for DZ twins. Therefore evidence suggests that due to fact antisocial behaviour is more prevalent in MZ twins compared to DZ, the assumption can be made that genes do influence aggression due to MZ twins having 100% of their genes in common compared to 50% for that of DZ twins. However the ability to give a genetic explanation for the evidence to provided by twin studies depends on the "equal environment assumption."
      2. Twin studies are praised for providing valuable insight into the role of genetic factors on aggressive behaviour. If there is a genetic contribution to aggression, studies should revel a relationship between the number of shared genes (100% MZ 50% DZ) and the concordance rate of aggression; the closer the genetic relationship, the higher the concordance rate. It can be assumed that if the environments are similar for both types of twins, then a higher rate of concordance for MZ twins can be interpreted as support for genetic factors on the likelihood of displaying aggressive behaviour.
        1. Rhee and Waldman (2002)
          1. Findings regarding the role of genes in aggression should be used with caution due to methodological issues. Rhee and Waldman suggest that the variability of the finding s may be partly due to the methods used to assess aggressive behaviour. Their meta-analysis of 51 twin and adoption studies indicated significant differences in the size of genetic and environmental effects depending on how aggression was measured.
          2. Miles and Carey (1997)
            1. Variability in the findings from twin studies, ranging from 0.14-0.72 for MZ twins, reduces the reliability of the findings obtained from twin studies into the effects of genes on aggressive behaviour.
          3. IDA
            1. Nature/Nurture
              1. The central debate is not about whether heredity or the environment is responsible for aggressive behaviour. Genetic factors do not work in isolation but alongside environmental factors, as shown by Caspi's research conducted into the MAOA gene. Hence the debate is about the extent to which these factors influence human development and more importantly the way that these factors interact with each other. Genes predispose an individual to displaying aggression, however these aggressive characteristics are only portrayed when exposed to certain environmental factors, such as domestic violence. Therefore findings regarding the infunece of genes on aggression should be used in conjunction with that of environmental factors to gain a more comprehensive explanation of aggression.
              2. Reductionism
                1. This Biological explanation of aggression may be considered reductionist as it is not possible to identify one single gene (/hormone/ neurotransmitter) responsible for aggressive behaviour. Genetic deficiencies may exert some influence on an individual's behaviour, however they are not the sole cause of aggressive behaviour.
                2. Determinsim
                  1. Genes do not determine behaviour, and only poorly predict the likelihood that an individual will display higher levels of aggression. Although the role of genetic influence is more straightforward in animal research, demonstrated in studies of selective breeding; the absolute genetic explanation ignores the role of environmental factors and their influence upon how genes are displayed (phenotype) Moreover the genetic explanation ignores free will and individual choices and suggests that we are not responsible for aggressive acts. This is considered controversial as it opposes the view of the judicial system in that humans have free will and are able to show restraint and not display anger through aggression. Therefore the absolute genetic explanation of aggression should be used with caution as it only partial insight into the factors affecting aggressive behaviour.
                3. Adoption Studies
                  1. Hutchings and Mendnick (1973)
                    1. Research conduced by Hutchingson and Mednick provides support for the effect of genes on aggressive behaviour. They found a significant positive correlation in over 1,300 adoptions between the number of violent convictions for criminal violence among the biological parents and the incidence of criminal violence among their adopted sons. This suggests that despite being separated from their biological parents, their inherited genes predisposed their sons to displaying aggression, depicting that genes have a major influence in aggression.
                    2. Tremblay (2003)
                      1. Research found that parents giving up their children for adoption displayed a higher level of aggression than adoptive parents. These findings however may be explained by social/psychological factors, such as anti-social behaviour and feelings of abandonment of the child. Therefore it is difficult to draw conclusions into the effect of genes on aggression.
                    3. MAOA Gene
                      1. Brunner et al (1993)
                        1. A study of Dutch family supported the role of genetic factors on aggressive behaviour as it was found that predominantly male members of the family behaved in a particularly aggessive/violent manner and a large proportion has been involvee in crimes such as rape/arson. Upon further investigation it was revealed that these men had abnormally low levels of MAOA in their bodies and a defect in this gene was later identified. Their reduced ability to breakdown dopamine and serotonin was responsible for their aggressive tendencies and was due to a genetic defect, depicting genetic factors do influence aggression.
                        2. Caspi et al (2002)
                          1. Research found that men with low levels of MAOA were significantly more likely to grow up to exhibit antisocial behaviour, but ONLY if they had been mistreated as children. On it's own the MAOA gene variant had no effect. Men with high levels fo MAOA/those not mistreated did not display antisocial behaviour. Therefore it can be concluded that inherited genes predisposed children to aggressive behaviour when maltreated themselves, highlighting the importance of the interaction between genetic and environmental factors.
                        3. Animal studies
                          1. Cairns (1983)
                            1. Research found that through selective breeding of mice, highly aggressive male and female mice were created who displayed aggression at abnormal parts during development (e.g. during middle age not youth.) This suggests that genes do play a role in an individuals likelihood to display aggression. Animal studies are praised for showing how aggressive behaviour can be produced through isolation and manipulation of aggressive genes.
                              1. Research conducted by Cairns can be criticised for anthropomorphism as it is considered inappropriate to compare the genetic make up of mice to that of humans. Humans are far more physiologically and cognitively advanced than mice, so therefore findings obtained from animal studies should be used with caution when explaining the effect of genetic factors on human aggession.
                                1. However research by Cairns can be praised for providing a valuable insight into the effects of genetic factors on aggression. Evolutionary psychologists would argue that since the same basic principles can be applied across species, findings obtained from animal studies can be used to explain the role of genes on human aggression
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