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AGGRESSION NOT IN JAN MOCK, Weakness: This view is deterministic. It…

- - - - Strength: Supportive research
        
        McBurnett et al 2000
        
        McBurnett conducted a longitudinal study of 38 boys who had been referred to a clinic for problematic behaviors. They measured testosterone levels with saliva tests, and also asked the boys to decide on the meanest amongst them.
        
        They found that the boys who had lower cortisol levels were labelled meanest and exhibited three time the amount of aggressive behaviors than those with higher cortisol levels. This supports the link between low cortisol and heightened aggression
        
        Dabbs et al
        
        Measured salivary testosterone in violent and non violent criminals
        
        Found that those with highest levels of testosterone had a history or predominantly violent crimes compared to non violent
  - - - Strength:
        
        Supportive research- Wagner et al studied aggression in mice. They found that when castrated, aggression levels decrease and when injected with testosterone, the aggression levels increase. This suggests that testosterone has a strong influence on aggressive behavior.
        
        Potegal et al states that non humans and humans are more similar than dissimilar, so we should be able to generalise with confidence
      - Weakness:
        
        Non- human. There are physiological differences between humans and non humans so we should take care when generalising
        
        Conflicting evidence: Some studies have found no relationship between aggression and testosterone. Most studies are correlational and show a relationship between the two variables, so it can be hard to establish cause and effect.
- - - - If there is a positive correlation between aggressive behavior in biological parents and aggressive behavior in the child, a genetic link is established
      - If there is a positive correlation between aggressive behaviour in the child and aggressive behaviour in the adoptive parents, an environmental link is established
    - - Strengths
        
        Supportive research
        
        Hutchings and Mednick: Studied 14,000 adoptions in Denmark and found that a significant number of the adopted boys with criminal convictions had biological fathers with convictions for criminal violence. This suggests a genetic link to aggression because the biological father couldn't have created a criminal environment for the child, as it was adopted, so genetic factors alone were enough to make the child a criminal.
        
        Miles and Carey 1999 carried out a meta analysis of 24 twin and adoption studies which demonstrated genetic influence on aggression. Their results suggested that genetics could account for as much as 50% of the variance of aggression.
        
        Rhee and Waldman did a meta analysis of 51 twin and adoption studies which focused on anti social aggressive behaviour. They also concluded that a large proportion of the behaviour had genetic influence
      - Weaknesses
        
        Issues with isolating genetic factors: It is extremely difficult to ignore the effect that an individuals environment has on thier behaviour, sometimes these two influences (genetic and environmental) are inseparable. Sometimes it is necessary for them to interact, for example, a person with a predisposition to violence usually needs to be provoked. This makes it difficult to measure genes exact influence
        
        Inconsistencies: Miles and Carey analysed studies which relied on self/parental report methods, and found a large proportion of variance to be due to genetics. However, studies which used observational techniques showed that genetics had significantly less of an influence, and that environmental influence was higher
  - - - Studied adult male DZ and MZ twins. For physical assault (aggression) researchers found concordance rates of 50% for MZ twins and 19% for DZ twins
      - Interpretation: as the MZ rates are significantly higher than the DZ ones we can infer that behaviour is party due to genetic factors
    - - Researchers compare the extent to which twins share a particular trait. Monozygotic (MZ) twins share 100% of their DNA code, while dizygotic (DZ) twins share on average 50% of their DNA code. Any phenotypic differences (aggressive behaviour) between monozygotic (MZ) twins is theoretically due to the environment.
      - Many twin studies have suggested that heritability (genetic factors) account for about 50% of the variance of genetic behaviour (the other 50% being due to the environment)
      - Interpretations
        
        If MZ concordance is significantly higher than DZ concordance, we can interpret that behavior is partly due to genetics, as the identical pair share more genetics and share more of the feature
        
        If MZ concordance is similar to DZ concordance we can interpret that behaviour was entirely due to upbringing (no genetic influence) as normally the genetically identical pair would have higher results but if they're similar then it means environment has affected both pair equally, genetics haven't influenced it
        
        If MZ concordance is 100% we can interpret that the feature is entirely due to genetics (no environmental influence) If the environment influenced it then, as no two people can share the exact same environment, there would be some sort of differences
        
        If MZ concordance is significantly less than 100% then we can interpret that the feature is partly due to nurture as the environment has had an influence and created a difference between the identical twins
  - - - The MAOA-L variant of the gene is known as the warrior gene, as lower levels of MAOA have been associated with low dopamine, which can cause aggression
      - A study of Finnish prisoners revealed that a MAOA-L (low-activity) genotype, which contributes to low dopamine turnover rate, was associated with extremely violent behavior. For the purpose of the study, "extremely violent behavior" was defined as at least ten committed homicides, attempted homicides or batteries
      - Studies have shown that a variation of the MAOA gene (MAOA-L) can influence brain activity in certain situations. Studies have shown that males are three times more likely to have the MAOA-L variation than women.
    - - Strengths
        
        Cases et al disabled the functioning of the MAOA gene in mice and found that without the MAOA enzyme, serotonin increased and subsequently violence increased to high levels. Restoring the function of the gene returned aggression to a normal stable low level. This suggests that MAOA gene can influence aggression
        
        Practical applications: The studies on anti social behaviour can be used he help rehabilitation and treatment of repeat offenders
        
        Caspi et al studied 500 male children longitudinally, and discovered that those with the MAOA-L variation were more likely to grow up and exhibit anti-social behaviour than those with the MAOA-H variant. This links the low activity variant to heightened aggression
      - Weaknesses
        
        Caspi also found that anti-social behaviour was not solely affected by having the MAOA-L gene, that this gene only led to anti-social behaviour when maltreated in childhood. This shows that genetics alone don't determine behaviour, there is an environmental influence.
        
        McDermott did a study of individuals with the MAOA-L and a control group. He found that when playing money allocation games, the MAOA-L group only showed aggression when provoked. If unprovoked, they displayed the same behaviour as the control group. This also suggests that genetics alone don't determine behaviour, but rather an interaction with external environmental factors
        
        Free will vs Determinism. The MAOA gene can be seen as biological determinism and therefore has issues with the legal system, are criminals responsible for their violence if their genes control their behaviour?
- - - - Strength: Supportive research. Raine et al, studied two groups of violent offenders, some who were caught and some who were not. Successful and unsucessful. The unsucessful group were seen to be more impulsive, and MRI scans revealed the unsuessful grou to frequently have different sizes of each half of the hippocampus, imablanced. This abnormality may have impaired hippocamus to amygdala communication and let to impulsive innapropriate violent responses
  - - - Weakness: conflicting evidence. Muller et al found that his 6 psychopaths had increased amygdala activity when viewing positive and negative pictures, compared to a control group of another 6. This conradicts Pardini as it suggests that increased amygdala functioning could be associated with higher levels of aggression, as opposed to low levels of activity causing aggression
      - Strength: supportive research. Pardini et al did a longitudinal study of males from childhood to adulthood. Using MRI scanners, they observed a link between lower amygdala volume thoughout one's life, and increased levels of aggression and violence in adulthood. This shows that the amygdala has an important role in creating an emotional respons and inhibion of this function due to decreased volume can more often lead to violece (incorredct response)
- - - - Supportive research
        
        Non-human species: Raleigh observed monkey's aggression levels and diets. They found that vervet monkeys, who ate a diet with high levels of tryptophan, which increases serotonin, had decreased levels of aggression compared to moneys fed on diets with low tryptophan. This suggests that the difference in behaviour could be due to thier different levels of serotonin, and links lower levels to hightened aggression
        
        Crockett et al had two groups of participants. One group had lowered levels of seroonin due to a restricted diet, and the other group had increased levels due to SSRIs. They had the participants play games against eachother and observed that the lower serotonin group tended to retaliate more strongly against opponents. This suggests that lowered serotonin can induce aggressive respones.
      - Pratical applications: Knowledge of serotonin and agression has been used in institutions, for juvenile delinquents and for institutionalised patients, increasing serotonin has helped to alleviate aggressive tendencies. this suggests that aggression can be more controlled which is good for society