Behavioural genetics in court : the impact of mitigating versus aggravating evidence, and recidivism

Evidence for genetically predisposed behaviours, particularly of impulsivity and aggression, has been presented in court cases, resulting in concern as to how persuasive this evidence might be. The present study aimed to determine if legal party presentation of behavioural genetic evidence, as well as inclusion of recidivism evidence, could differ the recommended sentencing and perceptions of the defendant. A total of 168 participants (females = 123) aged 18 to 75 were included and were randomly assigned to one of four conditions that included evidence presentation (defence or prosecution) and recidivism (first or fifth account). Participants read a vignette on an aggravated assault, diverging only by the conditions' differences, that included genetic evidence for the assailant having a genetic predisposition to impulsive and aggressive behaviours. Participants acted as mock jurors to recommend sentence severity and report perceptions of the defendant's culpability and dangerousness. It was determined that behavioural genetic evidence presentation by the defence resulted in slightly lower recommended sentence severity than the presentation by the prosecution, and that a history of recidivism resulted in a small increase in the perception of the defendant's dangerousness. The findings demonstrate that the prosecution could manipulate this evidence to aggravate a court case.