The biological explanations of aggression say that aggression is caused by differences in the biological make-up of individuals. One example of these biological differences that could cause aggression is genetic factors. We are unsure of why there may be a link between genetics and aggression; however research has found a correlation.
Twin Studies – Monozygotic (MZ) twins share all of their genetic information whilst dizygotic twins (DZ) share 50%. If MZ twins are more alike in terms of aggressive behaviour than DZ twins, then this should be due to genes rather than environment. It is much harder to study aggressive behaviour than criminal behaviour, so few studies have tried to measure aggressive behaviour directly. However, Coccaro did use twins to study aggressive behaviour and found that 50% of the aggression towards to each other could be attributed to genetic factors.
Adoption studies – One problem when studying twins is that twins will often be brought up together in a similar way, so it is hard to say whether the concordance rates are caused by genetic or environmental factors. To solve this problem psychologists can carry out adoption studies where they observe the levels of aggressive behaviour in adopted children and their biological parents. If there is a high correlation between aggression levels of the two you can say it is genetics not the environment that caused this aggression. Hutchings and Mednick (1975) studied 14,000 adopted children and found that a high proportion of boys with criminal convictions had biological parents with criminal convictions too, suggesting a link between aggression and genetics.
Genetic explanation for aggression
MAOA – The gene MAOA is responsible for the regulation of serotonin in the brain. Low levels of serotonin are thought to lead to aggressive behaviour, so a problem with MAOA could lead to aggressive behaviour. Brunner (1993) found that in a Dutch family with a history of serious aggressive crime the men had abnormally low levels of MAOA, supporting this explanation
Gene-environment interaction – This explanation says that it isn’t just genetics that causes aggression, it is a combination of the genetics and the environment that someone lives in that causes aggression. For example a study found that in a sample of children who had low levels of MAOA it was only the children who were maltreated that displayed antisocial behaviour.