Syllabus Edition
First teaching 2017
Last exams 2026
Genetic Factors in Aggression (AQA A Level Psychology): Revision Note
Exam code: 7182
A genetic explanation of aggression
Genetic explanations of aggression assume that aggressive behaviour is the result of inherited traits/characteristics that have adapted across generations because of their evolutionary usefulness
I.e., aggression is a trait necessary for survival
About 50% of the variance in aggressive behaviour is explained by genetics; 50% of variance is explained by environmental factors (Tuvblad & Baker 2013)
Genetic inheritance of traits is generally investigated using twin studies, as MZ twins share 100% of their DNA and they not only provide a control sample for each other but can be compared to DZ twins
Christiansen (1974) found 35% concordance for aggression between MZ twins but only 13% concordance for DZ twins
Rushton et al. (1986) found a correlation coefficient of 0.40 for MZ twins but only 0.04 for DZ twins
Adoption studies are also used to investigate genetic factors in aggression, as they may highlight differences between biological and adoptive parents and their children
Rhee & Waldman’s (2002) meta-analysis of 52 twin and adoption studies showed that environmental factors can only be an explanation for aggression if the specific genetic factors are already present
I.e., the environment alone is not enough to trigger aggression
The role of the MAOA gene in aggression
The MAOA (monoamine oxidase) gene (also known as the ‘warrior gene’) is an enzyme which is implicated in the regulation of key neurotransmitters, particularly serotonin
Serotonin has been linked to mood, specifically in the balancing of mood i.e. low or disrupted levels of serotonin may be a factor in affective disorders such as depression and also in aggressive behaviour
A dysfunctional MAOA gene may lead to an imbalance of serotonin and, possibly, to an increase in aggression
Brunner et al. (1993) found that aggressive males in one family all shared the same dysfunctional gene, which led to low levels of MAOA and, by extension, low levels of serotonin
Some research suggests that a faulty MAOA gene alone is not enough to produce aggressive behaviour; rather, it is the combination of a traumatic childhood with the faulty gene that is responsible for extreme aggression (Caspi et al. 2002)
Research which investigates genetic factors in aggression
Miles & Carey (1997) - Meta-analysis of 24 twin and adoption studies which found strong support for a genetic explanation of aggression; additionally, they found that environment was more influential during a person’s youth and genetics were more important (in determining aggressive behaviour) during adulthood
Reif et al. (2007) - 45% of aggressive participants had a faulty MAOA gene (low-activity, short allele), which was also linked to childhood trauma, i.e., there are complex interactions between genes, serotonin and environmental factors
Examiner Tips and Tricks
Make sure that you use specific terminology for questions on genetic factors in aggression, as it will demonstrate a mature and confident grasp of the topic.
Evaluation of genetic factors in aggression
Strengths
Biological evidence e.g. saliva samples and DNA analysis, is objective and can be measured by blind researchers, making it reliable
Twin and adoption studies tend to use large samples (e.g., Christiansen’s study above used 7000 twin pairs), which generates robust quantitative data
Weaknesses
If genetic factors alone were responsible for aggression, then concordance for MZ twins should always show a 100% concordance rate, which has never been the case
It is unlikely that the MAOA gene is solely responsible for aggression and, in fact, research in trying to establish which other genes may be involved in aggression is ongoing
Examiner Tips and Tricks
Examiners report that when answering a question on genetic factors in aggression, some students give answers that barely mention genetics but focus instead on neural explanations. This neural material could be made relevant if students linked it to a genetic explanation but this does not often happen and they lose marks as a result.
Issues & Debates
Genetic explanations exemplify the nature side of the nature vs nurture debate, suggesting aggression is inherited through genes
However, research (e.g., Caspi et al., 2002) shows that environmental triggers like childhood trauma interact with genes, supporting an interactionist approach
This suggests aggression is shaped by both genetic vulnerability and environmental experience
Genetic explanations imply a biological determinism, where individuals may be predisposed to aggressive behaviour due to their genes
This raises questions about moral responsibility, especially in legal contexts—can someone be held fully accountable if they carry a so-called “warrior gene”?
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