Nature, nurture, and capital punishment: How evidence of a genetic-environment interaction, future dangerousness, and deliberation affect sentencing decisions

The use of neurobiological evidence in sentencing mitigation

Neurobiological evidence has grown increasingly relevant in U.S. criminal proceedings, particularly during sentencing. Neuroimaging, such as functional Magnetic Resonance Imaging and Positron Emission Tomography scans, may be introduced by defense counsel to demonstrate brain abnormalities to argue for more lenient sentencing. This practice is common for penalty mitigation in cases eligible for capital punishment. This article reviews the history of the use of neuroscience in criminal cases from the early 20th Century to present, noting pertinent legal and ethical considerations for the use of such evidence. The authors review important empirical research conducted in recent years regarding the use of neurobiological evidence in legal proceedings (such as mock-juror studies) and guidance from the federal sentencing guidelines and the American Bar Association. The discussion also notes relevant case law in which neuroimaging, behavioral genetics, or other neurobiological data were introduced in criminal proceedings, particularly precedent-setting U.S. Supreme Court cases.

How information about perpetrators' nature and nurture influences assessments of their character, mental states, and deserved punishment

Evidence of perpetrators' biological or situational circumstances has been increasingly brought to bear in courtrooms. Yet, research findings are mixed as to whether this information influences folk evaluations of perpetrators' dispositions, and subsequently, evaluations of their deserved punishments. Previous research has not clearly dissociated the effects of information about perpetrators' genetic endowment versus their environmental circumstances. Additionally, most research has focused exclusively on violations involving extreme physical harm, often using mock capital sentences cases as examples. To address these gaps in the literature, we employed a "switched-at-birth" paradigm to investigate whether positive or negative information about perpetrators' genetic or environmental backgrounds influence evaluations of a perpetrator's mental states, character, and deserved punishment. Across three studies, we varied whether the transgression involved direct harm, an impure act that caused no harm, or a case of moral luck. The results indicate that negative genetic and environmental backgrounds influenced participants' evaluations of perpetrators' intentions, free will, and character, but did not influence participants' punishment decisions. Overall, these results replicate and extend existing findings suggesting that perpetrators' supposed extenuating circumstances may not mitigate the punishment that others assign to them.