23/24 Outline and evaluate the role of genetic factors in aggressive behaviour (24 marks)

Outline and evaluate the role of genetic factors in aggressive behaviour (24 marks)

The claim that aggression can be inherited through genes has been studied by a large number of psychologists. Twin studies have been particularly useful for exploring this biological explanation, and has allowed psychologists to look chiefly at genes; especially in monozygotic twins. Rutter found a higher concordance in aggression for MZ twins than DZ twins, suggesting that the more similar the genes are, the more likely they share genetic behaviour such as aggression. Coccaro found that nearly 50 % of the variance in direct aggressive behaviour in adults was attributed to genes and 70% of verbal aggression. However, this research also contradicts the role of genetics in aggression, as it gives equal weighting to environmental factors, which the other 50% of the variance is attributed to. This briefly outlines the gene-environment interaction approach, with a genetic predisposition reacting with the environment to influence aggressive behaviour. Adoption studies have also helped to differentiate between the complicated contributions of environment and heredity in aggression. If the adopted child and their biological parents display aggressive behaviour, it is likely that genetics play a stronger role than upbringing in a different environment Hutchings and Mednick studies 1400 adoptions in Denmark and found that a significant number of adopted boys with criminal convictions had biological parents (usually fathers) with criminal convictions. This supports that genetics influence aggression, as there is evidently a correlation even when separated from biological parents and the same environment. There is a problem that the only aggression measured was criminal convictions however, as it may not have picked up on antisocial behaviour not caught. In fact, with only studying criminal convictions, the psychologists could have ignored those who are arguably more intelligent and aggression- not having been caught and getting away with the crime.

There are some problems with twin studies. The first being that although MZ twins have a higher concordance rate for aggression in comparison with DZ twins, the concordance rate is never 100%. This suggests that genetic factors are not the only factors for aggression and environment does play a part. A predisposition for violence, but a disciplined and supportive home environment may stop this behaviour being a problem. Another problem is that MZ twins look exactly the same, and share the same biological makeup. This would affect how society treats the twins, perhaps the same way. In this instance, DZ twins would be treated more like individuals, and would therefore show more variance in their behaviour.

With both methodologies, criminality may be studies more than aggression, which affects internal validity. This means that the study fails to differentiate between violent and non-violent crime; an individual may have a conviction for fraud and placed in the same category as an individual in prison for manslaughter. Another issue is that habitual violence may be a better indicator for aggression, but again is placed in the same category as a one-off crime (a person who became aggressive once after consuming alcohol and bumping into someone they both had a mutual hatred for each other). Mednick et al found the biggest effect in their study was for non-violent crime. Brennan, however, compared the criminal history of adopted males and their biological and adoptive parents. They found that genetic influences were significant in cases of property but not violent crime. This piece of research shows that a crime personality may be inherited rather than aggressive behaviour. Being in a demonstratively moral and supportive environment teaches children not to be aggressive instead of becoming desensitised to it in a genetically likely household with many convictions.

Gender bias has also been criticised in the study of the role of genetics in aggression. Button et al found that the genetic heritability of aggressive anti-social behaviour was much higher for girls than boys (this was not the case for non-aggressive anti-social behaviour such as truancy). Button’s research indicates that heritability is stronger in women than men when it comes to aggression, and that more research would need to be taken for females. This may also explain the lower concordance in same sex DZ twins.

Other psychologists have explained the genetic link to aggression with a single gene- the MAOA. This warrior gene is linked with aggression, with lower levels increasing aggression. This may be dues to the role it has on regulating the metabolism of serotonin on the brain, with lower levels increasing aggression.  Brunner studied a Dutch family with the males showing high levels of violence (convictions and high antisocial behaviour levels). The study found abnormally low levels of MAOA, showing that deficiencies cause aggression. This study is culturally bound, and may not be demonstrative of the link between aggression and genes around the rest of the world. However, a gene-environment explanation may carry more weight. Caspi conducted a meta-analysis with 500 male children. He found that low levels of MAOA in the children did concord with antisocial behaviour, supportive of this explanation, however only if maltreated as a child. This shows that social environment plus genes influences behaviour, rather than just one or the other. Moffat found a similar conclusion. By examining abuse, convictions, violence and antisocial behaviour in 422 males from New Zealand, low levels of MAOA correlated with the risk of being convicted but again, only if they had suffered abuse. All of these studies are based on male aggression, with no incidences of female aggression. This is a weakness, which means that genes can only be shown to influence aggression on men.

Research into MAOA on aggression, like twin and adoption studies, focuses on individuals who have been convicted of violent crimes. This means that the studies only involve aggressive individuals who have been caught- who may tend to be low-intelligence individuals. This may explain why many studies fail to find evidence of genetic influences on aggression. They also fail to explain cultural differences which suggests that genetics are not the only factors in aggression, otherwise it would be universally correlated. In this way, the MAOA gene’s studies are ethnocentric, unable to be generalised to other countries.

However, research into this gene may be useful for society and the individual. Morley and Hall suggest that information from genetic screenings could be used to devise new treatments for personality disorders that have been identified as risk factors for criminal behaviours. The treatment would be able to lower the risk of the person being put in prison, and create a safer society. However, there are ethical weaknesses with this. This is rather deterministic, stating that the person will be aggressive after being labelled with MAMO deficiencies and is not pleasant for the person. Because it is their genetic makeup, this may seem like their personality is being altered when there is really only 50% variance linked to aggression. It could be useful when environmental factors pose a risk for those also with low levels of MAOA.

Many studies of genetic influences on aggressive behaviour rely on self-reports and these studies tend to show that there is a genetic link for aggression. However, observational studies have not been consistent. Miles and Carey found less genetic influence on aggression through observation than with self-reports in a meta-analysis. A replication of Bandura’s Bobo study using twins found no difference in MZ and DZ twins, suggesting that individual differences in aggression were more of a product of environmental influences than genetics (Plomin). This research suggests that many studies into MAOA are inconsistent, and the link found is unpredictable. Morley and Hall argue that genes associated with aggression only poorly predict the likelihood that an individual will display aggressive behaviour. The presence or absence of environmental factors can’t be identified in a genetic text, making the prediction of aggression even less likely. Perhaps a gene-environment interaction is a better explanation, with those who are predisposed genetically and brought up in a low socio-economic background more prone than those predisposed and brought up in a higher socio-economic environment in an area with low crime rates. If both genes and environment are not good predictor, then used in synchronisation will increase the accuracy.

The role of genetics is reductionist, as is states that aggression is caused by a single gene to make it easy to test. It ignores complex biological factors as well as psychological and environmental factors. For example, MAOA decreases low serotonin levels. Low serotonin levels are correlated with increased risk for depression. It could be that they are testing depression in males, as aggression and violence are symptoms of male depression (especially if they had suffered mistreatment as a child).  It is also determinist, showing that aggression is determined by our genes and that we can treat people with “faulty” genes. The biological approach ignores free will and this reduces individual responsibility for aggression, a significant problem when addressing an issue which is frequently dealt with in court and is harmful to society.