top of page

Are gene predispositions enough to justify our violent behaviours?

Updated: Jan 20

By Eloise Williams - United Kingdom


The Nature vs Nurture debate is one agonised over constantly by psychologists. The increasing developments in technology and cognitive neuroscience means the nature side of the argument is becoming increasingly compelling.


Real life events


In Italy in 2009, the sentence of a convicted murderer was controversially cut from 9 years to 8 on the basis that he had a variant of the MAOA gene that has links to aggressive behaviour. Abdelmalek Bayout, a diagnosed schizophrenic, admitted to stabbing and killing a man during a psychotic episode after he, against medical advice, discontinued his psychotropic medication (Callaway, 2009). Although his chronic brain disorder, schizophrenia, influenced the judge’s decision, that he was not in the right state of mind to be capable of fully understanding the gravity of his actions, what makes this case so dubious is the primary role that ‘blaming’ the genes had on this criminals reduced sentence and the lack of evidence behind the gene research used. This is because most tests performed on Bayout were still purely research-based with no formal clinical evaluation (Hunter, 2010). Therefore, some psychologists argue there was hardly enough evidence to prove Bayout had genes that would provide him with uncontrollable aggressive behaviour, and not nearly enough for this to have utility as evidence in court. Others, including Lewis LS, said we should ‘serve the broad principle of justice that punishment of a crime be proportional to one’s blameworthiness’.


Explanation of gene


Monoamine oxidase A - MAOA -  encodes monoamine oxidase, an enzyme that degrades amine neurotransmitters such as dopamine, noradrenaline and serotonin. A rare genetic disorder leads to MAOA deficiency due to an excess of monoamine transmitters causes impulsive behaviours, including hypersexuality, sleep disorders, and extreme mood swings, as well as a tendency to be violent. This is known as Brunner syndrome, named after the psychologist Jerome Brunner who is known for his extensive research in the field of genetics. Brunner syndrome is an X-linked disorder characterised by impulsive aggressiveness and mild retardation associated with MAOA deficiency ("“Warrior Gene” Predicts Aggressive Behavior After Provocation.", 2009). There are two forms of the MAOA gene: MAOA-H and MAOA-L. MAOA-L includes people with the low-activity form, where they produce less of the enzyme, while MAOA-H constitutes the high-activity form, where more of the enzyme is produced. MAOA-L is the gene that in pop-psych is nicknamed the ‘warrior gene’ or the ‘psychopath gene’ due to its link to aggressive and violent behaviours. This gene is surprisingly common, with The National Library of Medicine predicting 40% of the population to have this gene. While people with high levels of MAOA are reportedly more likely to experience major depression, suicide, and sleep disturbances due to them receiving fewer neurotransmitters, such as dopamine and serotonin, which can improve their mood. Therefore, we are particularly interested in low levels of MAOA in these studies (Hunter, 2010).


Gene research


In 1993, Brunner studied the behaviour of a large family in the Netherlands that carried the MAOA-L gene (“Brunner et al.”, 2014). The males in this family showed borderline mental retardation with an average IQ of 85; they also exhibited behaviours such as attempted rape, impulsive aggression, and arson ("Genetic Explanations of Offending Behaviour", 2021). Two females in the family were also carriers of the gene, and one non-carrier female who was the control. Brunner carried out a quasi-experiment, an experiment that used already naturally existing groups that had not been manipulated by anyone but did not include randomisation, and found that all the males acted aggressively when angry, fearful, or frustrated. Brunner then linked this to the base change he found in the DNA of all five men, where they had flawed monoamine metabolisms leading to their deficiencies in MAOA (“Brunner et al”, 2014). However, he found that the women did not display the same aggressive behaviour as the men. This could be linked to the X chromosome being responsible for producing MAOA. Hence why the men with XY chromosomes were more affected than the women with XX chromosomes who’s alternative X chromosome should ‘shut it off’. Even if the women have faulty production of MAOA on one chromosome they have another chromosome with a ‘normal’ allele (“Brunner et al”, 2014). In this field, there is also circumstantial evidence that another gene protects women from violent predispositions, however there is unsubstantial evidence to back up this theory. Though, this may be the reason why 80.1% of violent crimes are committed by men: if they have a higher probability of producing MAOA ("Crime in the United States 2012.", 2012).


Conversely, it is essential to note that even within this family from the Netherlands not all the males in the family had the inability to control their aggression, even if they also had mental retardation, suggesting some other factors are at play here. The males’ behaviours might not be explained solely by the lack of MAOA. Some problems with Brunner et al's research include the small sample size that he used; this one family arguably cannot provide enough evidence to be applied to the rest of the world. Therefore it lacks generalisability. (“Genetic Factors In Aggression, Including the MAOA Gene”, 2021).


Technological innovations


Research into genetic predispositions of behaviours has advanced with technological innovations, including Meyer, who used MRI scans to identify that people with MAOA-L are more likely to have a smaller limbic system. The limbic system is the part of the brain involved in behaviour and emotional control, implying people with MAOA-L are less developed in this section and would have less control over their emotional responses. Meyer et al also performed functional MRI which measures changes in the blood flow; this showed that the MAOA-L group displayed hyperresponsiveness of the amygdala -  the part of your brain in the Limbic system that is associated with emotional processing - during tasks. The scans showed the MAOA-L group was less able to inhibit strong emotional impulses, meaning they are less able to control their emotions and emotional actions. However, it is important to interpret Meyer’s group’s findings with caution. Ahman Hariri from the Institute for Genome, Sciences & Policy  thought  it was a ‘significant basic science finding linking genes to brain behaviour' but, ‘not a significant clinical finding,’ it only showed a subtle bias in the brain that tips the balance toward an aggressive response to provocation. Meyer himself noted that the MAOA-L gene is just one of several genes – many of which are still unidentified – that increase the risk of violent or antisocial behaviour ("“Warrior Gene” Predicts Aggressive Behavior After Provocation.", 2009).  


Conclusion


To conclude these findings, I think it is important to refer back to the nature and nurture debate mentioned at the start. From my research, it is clear that the growing speculation over the causality of genes and behavioural characteristics is increasingly relevant and fascinating. However, we need to appreciate that you cannot have one without the other. It is not possible for something to be solely the cause of nature and vice versa; therefore it is important to note that cases of the ‘psychopath’ gene MAOA-L causing violent actions from a criminal are often paired with a trigger from their nurture. For example, the presence of the MAOA-L gene alone is not going to be extraordinarily likely to cause violent behaviours. We can see this through there being a larger percentage of people with the MAOA-L gene (40%) than people who are psychotic and commit violent crimes (3.9%) (Hunter, 2010). However, if it is paired with maltreatment as a child or a cruel upbringing, then often this is when we see extremely violent actions. It is also important that genetic tests in forensic contexts, for example the case of Bayout in 2009, is restricted to tests with proven clinical utility, in order for genetic bases to be used as evidence, if it is used as evidence at all. It is the belief of Anthony Walsh that “Taking genetic factors into account when sentencing is plain stupid, unless we are talking about something like Down's syndrome or some other syndrome that drastically reduces intelligence and executive functioning,”. 


Bibliography


Hunter, Philip. “The psycho gene.” EMBO reports vol. 11,9 (2010): 667-9. doi:10.1038/embor.2010.122


"Genetic Factors In Aggression, Including The MAOA Gene." Psychology Hub, 17 Mar. 2021, www.psychologyhub.co.uk/student-resources/paper-3-aggression/genetic-factors-including-the-maoa-gene/?expand_article=1. Accessed 10 Dec. 2023.


"Genetic Explanations of Offending Behaviour." Tutor2u, 22 Mar. 2021, www.tutor2u.net/psychology/reference/genetic-explanations-of-offending-behaviour. Accessed 10 Dec. 2023.


Callaway, Ewen. "Murderer with 'aggression Genes' Gets Sentence Cut." New Scientist, 3 Nov. 2009, www.newscientist.com/article/dn18098-murderer-with-aggression-genes-gets-sentence-cut/#:~:text=act%3F,9%20years%20and%202%20months. Accessed 10 Dec. 2023.


"Brunner Et Al,. (1993) - Genes and Serotonin." Psych Yogi, 16 Sept. 2014, psychyogi.org/brunner-et-al-1993/. Accessed 10 Dec. 2023.



"“Warrior Gene” Predicts Aggressive Behavior After Provocation." News from Brown, 19 Jan. 2009, news.brown.edu/articles/2009/01/hotsauce#:~:text=The%20enzyme%20is%20regulated%20by,produces%20more%20of%20the%20enzyme. Accessed 10 Dec. 2023.





86 views0 comments

Recent Posts

See All

コメント


bottom of page