Courts’ Increasing Consideration of Behavioral Genetics Evidence in Criminal Cases: Results of a Longitudinal Study

82 Pages Posted: 23 May 2012 Last revised: 28 May 2012

Date Written: 2011


This article, which is part of a symposium honoring David Baldus, presents a unique study of all criminal cases (totaling thirty-three) that addressed behavioral genetics evidence from June 1, 2007, to July 1, 2011. The study builds upon this author’s prior research on all criminal cases (totaling forty-eight) that used such evidence during the preceding thirteen years (1994-2007). This combined collection of eighty-one criminal cases employing behavioral genetics evidence offers a rich context for determining how the criminal justice system has been handling genetics factors for nearly two decades, but also why the last four years reveal particularly important discoveries. Results suggest that not only is much of the controversy surrounding behavioral genetics and crime unwarranted, the use of such evidence has been misunderstood.

Within the last four years, for example, behavioral genetics evidence has appeared to have been applied almost exclusively as mitigating evidence in death penalty cases and primarily in two ways to support claims of ineffective assistance of counsel for neglecting such evidence or to provide proof and diagnosis of a defendant’s mitigating condition. Strikingly, this study found no case during 2007-2011 in which behavioral genetics factors were introduced by the State, much less used as aggravating evidence or as indications that a defendant would be a future danger to others. These findings debunk arguments that such evidence will be legally detrimental to a defendant. Indeed, in most cases, the evidence is so tightly intertwined with other factors in a defendant’s life that the particular impact of behavioral genetics can be difficult to isolate. This study’s results suggest that, at the very least, behavioral genetics evidence has no decipherable impact on a defendant’s case or, at most, it becomes an effective tool along with a range of other kinds of variables in rendering a defendant ineligible for the death penalty. Courts appear willing to accept behavioral genetics evidence as part of a defendant’s mitigation story, even if genetics renders that story a more troubling one in terms of the defendant’s purported propensities. The last four years also showed a number of break-a-way trends from earlier years. For example, there were substantially more cases that incorporated behavioral genetics evidence of any kind. In addition, there was a clear increase in the number of cases in which defendants submitted proof of a genetic propensity for alcoholism and/or substance abuse.

Overall, this article’s research shows that courts accept behavioral genetics evidence in the majority of cases in which defense attorneys attempt to offer it. The coming years will reveal whether such trends will be affected by Cullen v. Pinholster, the Supreme Court’s recent decision restricting prisoners’ efforts to seek federal habeas relief under AEDPA. Regardless, behavioral genetics evidence seems, on the surface, to have reached a status commensurate with other kinds of evidence without the baggage of abuse with which it has typically been associated.

Keywords: genetics, neuroscience, crime, criminality, logitudinal study, death penalty, mitigating factors, aggravating factors, alcohol addiction, substance abuse addiction, courts, judges, Cullen v. Pinholster, AEDPA

Suggested Citation

Denno, Deborah W., Courts’ Increasing Consideration of Behavioral Genetics Evidence in Criminal Cases: Results of a Longitudinal Study (2011). Michigan State Law Review, Vol. 2011, pp. 967-1047, 2011, Fordham Law Legal Studies Research Paper No. 2065523, Available at SSRN:

Deborah W. Denno (Contact Author)

Fordham University School of Law ( email )

Fordham University School of Law
150 West 62nd Street
New York, NY 10023
United States
212-636-6868 (Phone)
212-636-6899 (Fax)

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