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Mock jury study – will behavioral genetic evidence get defendants off the hook?

29 September 2017

Around the world, neuroscience evidence is being introduced into courtrooms at an increasing rate, including findings from behavioural genetics.

Specifically, some legal teams for the defence have been allowed to argue that the defendant has a low activity version of the MAOA gene, which codes for an enzyme that regulates the levels of several neurotransmitters. 

In combination with experiencing child abuse or maltreatment, having this low activity gene has been linked with increased impulsivity, including aggression. Defense lawyers presumably hope that jurors will interpret this as meaning the defendant was less culpable for their violent crime. However, before now, little research has examined how jurors will treat this evidence.

For a new study in Behavioral Sciences and the Law, Natalie Gordon and Edie Greene presented 600 mock jurors (half were students, half were from the wider community) with a detailed trial summary based on a real US murder trial in which the defendant, already in jail for an earlier crime, had murdered his cell-mate. The jurors’ task was to decide whether he should face the death penalty.

The jurors were presented with different versions of the trial – for example, some read that a medical geneticist had described the gene-environment interaction (that the defendant had the low activity MAOA gene and had suffered maltreatment as a child, which can lead to increased impulsivity); others read only about genetic evidence; others only heard about the environmental factor (maltreated as a child). The jurors also read about evidence from a clinical psychologist about whether the defendant was high or low risk for being dangerously violent in the future.

Read more on our Research Digest blog.


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