Nature VS Nurture – What extent aggression is due to genetic factors. Psychologists look at levels of aggression in closely related individuals as levels of aggression between the two individuals will be more similar if closely related (If aggressive behaviour is down to genes). Twin Studies Levels of aggression in Mono-zygotic twins (who share 100% of genes) are compared with levels of aggression in Dizygotic Twins (who share 50% of genes). Similarities in aggressive behaviour should be greater in mono-zygotic twins if genetic factors ARE a significant factor.
1. Using twins in studies enables researchers to control extraneous variables such as environmental factors as Mz and Dz twins will have been brought up in the same environment. 1. However, it is argued that Mono-zygotic twins may be treated more similarly than Di-zygotic twins. Adoption Studies Researchers compare an adopted child with either a biological parent or their adoptive parent. If genetics is a major factor of aggression, then we would expect similarity between child and biological parents. (E.g. father has history of violent crimes).
1. Difficult to tell whether aggressive behaviour is due to extraneous variables. Gene for aggression Monoamine Oxidase A Gene responsible for producing a protein called monoamine oxidase A (MAOA) has been associated with aggressive behaviour. MAOA regulates the metabolism of serotonin in the brain and low levels of serotonin are associated with impulsive and aggressive behaviour. Has been found that if this gene is faulty – it often results in aggressive behaviour.
1. Adoptive studies show that the highest rates of criminal violence in adopted children occur when both biological AND adoptive parents have a history of violent crime – gene-environment interaction. May be extraneous variables which cause aggressive behaviour – hard to entirely blame faulty gene. 1. Claimed that inherited temperamental or personality characteristics place some individuals more at risk of committing violent crime. A02 Research Evidence with criticisms Coccaro (1997) – Mono-zygotic twins studied – 50% variance in aggression due to genetic factors. 1. However – This leaves significant scope for influence of nurture rather than nature and may be difficult to apply findings. 2. Capsi study found variant of MAOA was only associated with aggression when children had been maltreated – shows environmental factor is large part of aggression.
Hutchings & Mendick – Found that adopted boys with criminal convictions were likely to have biological fathers with criminal convictions. 1. However – Criminal convictions are not a valid measure of aggression. Brunner – Found in one family a variation of MAOA gene was associated with aggressive behaviour. 1. However – aggression could still be explained by environmental factors. 2. This was a case study – so the findings cannot be generalised. Evidence is complex – clearly environmental factors which interact with genetics – cannot narrow it down to one or the other.
Also, problems measuring aggression – Miles & Carey found research using self-reports indicated higher genetic contribution than observations. Wider Issues Ethical Issues – The suggestion that aggression and criminal behaviour can be inherited raises ethical issues. If people are predisposed towards aggressive behaviour or violent crime, then questions about the treatment of such behaviours inevitably arise. Some suggest genetic engineering. It also raises questions about whether those who commit crimes may not be accountable for their actions if it is purely hereditary. Use of Non-human animals – Young et al (2002) – Researchers claim to have identified a genetic mutation that causes violent behaviour in mice. Humans are not the same as mice. May not be applicable to us.