the double-helix takes the witness stand

cell |  Advances in understanding genetic predispositions to behavioral and neuropsychiatric syndromes are squarely in the sights of the legal profession. With data suggesting substantial genetic contributions to the risk for criminal behavior (Tuvblad et al., 2011), attorneys have begun to explore the potential uses of genetic evidence in their clients’ defense (Denno, 2011). In addition, the first signs that genetic data may be of interest to the civil justice system have begun to appear. As is true whenever scientific data are introduced in court, these developments hold potential for assisting judges and juries with some of the difficult judgments that they face—but they also bring a substantial risk of misinterpretation and misuse.

In considering current and future uses of behavioral and neuropsychiatric genetic evidence, the unhappy history of genetics in the courtroom cannot be ignored. Even before the structure of DNA was identified and the transmission of genetic information elucidated, courts recognized that behavioral traits could be handed down in families. However, judges’ understanding of genetics typically reflected the science of the day, and the consequences of their reliance on contemporary knowledge were not always salutary. For example, in the U.S. Supreme Court’s decision in Buck v. Bell (274 U.S. 200, 1927), which upheld Virginia’s involuntary sterilization statute, Justice Oliver Wendell Holmes, appealing to the popular view that intellectual disability was passed from parent to child and was associated with promiscuity and crime, notoriously declared, “It is better for all the world, if instead of waiting to execute degenerate offspring for crime, or to let them starve for their imbecility, society can prevent those who are manifestly unfit from continuing their kind.”

Presumptions about the relationship between crime and hereditary intellectual deficiencies appear to have influenced the lower courts as well, with defendants who were viewed as “defective delinquents” often sent to state institutions where they could be confined indefinitely, rather than being sentenced to a fixed term in a correctional facility (Willrich, 1998). But the first use of genetic tests in the courts for their presumed relationship to criminal behavior did not arrive until the late 1960s and was based on data purporting to show that the XYY karyotype was linked to violent crime (Denno, 1996). Derived from a number of studies demonstrating overrepresentation of XYY men in correctional populations, the data were recruited by enterprising defense attorneys to argue that their clients’ violence was driven by genetic factors beyond their control, and thus that they could not be held criminally responsible for their behavior. Courts, however, were skeptical about the validity of data suggesting a causal link between the XYY karyotype and violent behavior and generally declined to admit karyotyping of defendants into evidence. As it turned out, the courts’ skepticism was fully justified—the purported link between XYY and violence has never been generally accepted (Stochholm et al., 2012).