The Use of Behavioural Genetic Evidence in Court

BIOLOGY

The Use of Behavioural Genetic Evidence in Court

Charlotte Fox

Roughly a third of Caucasian men carry an allele with a low activity of monoamine oxidase A, also known as MAOA, which is an enzyme controlling the metabolism of neurotransmitters, such as serotonin and dopamine, which influence brain function (1). It is suggested that low MAOA levels result in a person being more likely to commit a crime. Although a complete absence of MAOA function is extremely rare, the low activity MAOA version has been nicknamed the ‘warrior gene’, due to the impacts that it has on its carrier. For example, according to research published in 1993, five male members of a Dutch family were found to have no MAOA function, and this was used to explain why they displayed a low IQ and abnormal behaviour, such as impulse aggression (2). In addition, research that shows that 56% of Polynesian men have low MAOA levels, and this was used to explain problems of ‘risky’ behaviour and crime (3). However, critics of this research gave alternative explanations for the high conviction rate amongst Polynesian men, such as environmental factors.

Proof that a criminal has this MAOA version of a gene is often used in the US to avoid the punishment of the death penalty, because the combination of this genetic trait, along with trauma such as neglect or abuse during childhood, is associated with increased criminal behaviour (4). Multiple highly publicized cases have shown the possible impact of behavioral genetic evidence in court. For example, in 2007, Abdelmalek Bayout admitted to killing a man. His sentence was reduced by three years after the judge learnt that he suffered from mental illnesses as this was classed as a mitigating factor. At an appeal in 2009, a judge asked for a psychiatric report, and a molecular scientist was proved that that Bayout carried the low activity MAOA gene (5). Overall, the largest review of American court cases showed no substantial effect of behavioral genetic evidence on criminal sentencing, except a few cases in which it contributed to a jury’s decision not to enforce the death penalty.

Image showing how a low MAOA, in combination with a possible adverse environment, such as neglect or childhood abuse, can affect brain function and lead to altered behaviors.

Graph showing the correlation between antisocial behavior, childhood maltreatment and MAOA activity.

BIOLOGY

There are many problems with linking this particular gene to criminal behaviour, including the fact that a variety of behaviour is considered to be aggressive, and that the gene is too common in the male population to provide strong evidence for why certain people are more violent than others. Therefore, it is difficult to show the impact of the allele on an individual, rather than in people in general.

Research is being conducted to further explore the effects of the low activity MAOA gene in more detail (6), meaning that in the future, it is likely that behavioural genetic evidence will have a very large impact in the criminal court.

Sources:

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4865459/ 2. https://www.discovermagazine.com/the-sciences/a-violence-in-the-blood 3. https://www.nature.com/articles/jhg201219 4. https://www.pnas.org/content/106/7/2118 5. https://www.nature.com/news/2009/091030/full/news.2009.1050.html?message=remove&s=news_ rss&utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+news%2Frss%2Fmost_re cent+(NatureNews+-+Most+recent+articles) 6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4865459/