Behavioural Genetics in Criminal Cases: Past, Present, and Future

Researchers studying human behavioral genetics have made significant scientific progress in enhancing our understanding of the relative contributions of genetics and the environment in observed variations in human behavior. Quickly outpacing the advances in the science are its applications in the criminal justice system. Already, human behavioral genetics research has been introduced in the U.S. criminal justice system, and its use will only become more prevalent. This essay discusses the recent historical use of behavioral genetics in criminal cases, recent advances in two gene variants of particular interest in the criminal law, MAOA and SLC6A4, the recent expert testimony on behalf of criminal defendants with respect to these two gene variants, and the future direction of behavioral genetics evidence in criminal cases. Use of Human Behavioural Genetics in Criminal Cases With increasing frequency, practitioners in the U.S. criminal justice system have introduced expert testimony regarding the biological predispositions of criminal defendants, thus far with limited success. With the scientific research still in its infancy, criminal defendants have encountered significant hurdles when introducing expert testimony into U.S. criminal courtrooms regarding behavioural genetics. These defendants have primarily failed in their attempts because of the inadequacy of the science, the theoretical incompatibility of the evidence with the claim advanced, or because of procedural issues in U.S. criminal law barring the introduction of such evidence. In several cases, criminal defendants have introduced biological predisposition testimony in an attempt to negate the presumption they acted voluntarily in the commission of the crime. The majority of defendants to advance such claims have done so in the context of drug or alcohol addiction. In these cases, the defendant claims to have acted involuntarily as a consequence of his drug or alcohol addiction, for which he had a genetic predisposition. This claim has largely failed primarily because it is at odds with the firmly rooted position in the U.S. criminal law that voluntary intoxication cannot serve to excuse criminal conduct. In contexts other than addiction, however, American courts have demonstrated some willingness to entertain the claim that a defendant’s biological predisposition negates the voluntary act prerequisite for criminal liability. In the 2004 case of Herman Henry ‘Bud’ Von Dohlen, for example, the Supreme Court of South Carolina found persuasive the argument that the defendant’s mental disease, severe depression arising from a genetic predisposition, rendered the homicide a product of disease, disassociated from the will, rather than a voluntary criminal act by the defendant. Von Dohlen was convicted and sentenced to death for the armed robbery and murder of a dry-cleaning shop employee he fatally shot in the back of the head. In support of his claim for post-conviction relief, a psychologist testified that as a result of ‘his altered mental state ‘[the murder] was not a volitional thing but out of his conscious awareness or Genomics, Society and Policy 2006, Vol.2, No.1, pp.72–79.