comment Behavioural genetics in criminal court Introduction of genetic evidence of a predisposition to violent or impulsive behaviour is on the rise in criminal trials. However, a panoply of data suggests that such evidence is inefective at reducing judgements of culpability and punishment, and therefore its use in the legal process is likely to diminish.
Nicholas Scurich and Paul S. Appelbaum
ehavioural genetics, once largely the preserve of scientists exploring Bthe relative influences of heredity and environment on behavioural traits, is now an increasingly frequent visitor in the courts1. The interest of attorneys — particularly the criminal defence bar — in the genetic roots of behaviour lies in the presumed effect of genetic explanations on perceptions of individual responsibility. If a defendant’s criminal behaviour, rather than being determined by conscious choices, were driven by unconscious genetic predispositions to commit antisocial acts, the person may seem less responsible for the outcome and therefore less deserving of punishment2. Behavioural genetics, at least in principle, thus has become a tool for legal claims of reduced culpability and mitigated punishment. The future of its use in criminal trials, however, is less clear. The science behind the legal Credits: Gavel: Neustockimages/E /Getty; DNA: Martin Shields/Moment/Getty argument is based on studies that have + found an association between certain genetic variants, often interacting with from settled, the admission of behavioural How efective is behavioural genetic childhood maltreatment, and impulsive genetic evidence into court proceedings evidence? or antisocial behaviour3. One of the most is on the rise, especially in death penalty Several highly publicized cases have influential such reports analysed data cases, in which criminal defendants have illustrated the potential impact of from a longitudinal epidemiologic study sought to introduce behavioural genetic behavioural genetic evidence. Two convicted of a birth cohort in Dunedin, New Zealand, evidence in sentencing hearings to argue for murderers in Italy successfully proffered examining high- and low-activity mitigation1. Behavioural genetics appears such evidence to reduce their terms of polymorphisms in the promoter region to be part of a growing trend in criminal imprisonment6. In one case, the trial judge of the monoamine oxidase A (MAOA) cases of introducing evidence based on reduced the defendant’s sentence by three gene on the X chromosome in male neuroscientific methods — including years after learning that he suffered from subjects. The investigators found a gene- functional magnetic resonance imaging mental illness; an appellate court reduced his by-environment interaction between (fMRI) studies and neuropsychological sentence by an additional year on being told a history of childhood maltreatment testing — to address responsibility and that the defendant possessed a low-activity and MAOA status: subjects with an punishment5. While still controversial, MAOA allele. Less than two years after this allele associated with reduced MAOA some legal theorists have suggested holding, another defendant — who was production who had a history of that behavioural genetic and other convicted of killing her sister, burning the childhood maltreatment made up only neuroscientific evidence has the potential corpse, and attempting to kill her parents — 12% of the sample but accounted for 44% to undermine legal notions of free will, had her sentence reduced from life in prison of convictions for violent crime4. and therefore drive a reorientation of the without parole to a term of twenty years, in Although the exact relationship between criminal justice system from punishment part because it was discovered that she had a specific genes and antisocial behaviour is far to rehabilitation. low-activity MAOA gene.
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However, more systematic data call into Explaining the null efect How likely is genetic and neurobiological question the impact of behavioural genetic Several possibilities might explain why research to overcome these limitations? evidence. Notably, the largest systematic behavioural genetics fails consistently As Buckholtz and Meyer-Lindenberg10 review of American court cases found no to affect culpability judgements and note, studies have identified a number of discernible overall effect of behavioural punishment decisions in experimental changes in brain structure and function genetic evidence on criminal sentencing, settings. One is that biogenetic in men with the MAOA-L allele that can notwithstanding one instance in which it explanations for behaviour appear to plausibly be linked to increased impulsive seemed to contribute to a jury’s decision not induce countervailing beliefs, leading both aggression. These include reduced grey to sentence a murder defendant to death1. to the perception that persons are less matter volume in the amygdala and (Given that this analysis focused exclusively blameworthy for their behaviour but also cingulate gyrus, increased activation of the on appellate decisions — representing a that they are more likely to commit such acts amygdala and other brain regions associated small percentage of criminal cases — limits again. Thus, the net effect of behavioural with emotional responses, and diminished inherent in the data could account for the genetic evidence may be null. activity in areas that modulate such failure to ascertain an effect of behavioural An additional possibility is that the lay reactions, including the anterior cingulate. genetic evidence in court.) public simply does not comprehend the Yet, most studies of the relationship of Researchers have also started to examine intricacies of behavioural genetic evidence MAOA-L alleles to violence have shown no experimentally the effect that such evidence and therefore ignores it when rendering effect of the low-producing allele per se, might have on culpability and sentencing decisions about culpability. Yet another in the absence of indicators of childhood decisions. One study found that a sample of option is that the lay public does not view maltreatment — suggesting that these US state court judges reduced a hypothetical genes as the primary or even the major alterations in themselves are insufficient to defendant’s average prison sentence by determinant of behaviour, and therefore account for increased violence risk. To our less than one year (from approximately finds evidence of a genetic predisposition knowledge, comparable studies of brain 14 years in the control condition to about to be of little relevance in determining structure and function in subjects having 13 years) when behavioural genetic evidence culpability or imposing punishment. both the MAOA-L allele and a history was proffered to support the diagnosis of Or judges and the lay public alike may of maltreatment in childhood have not psychopathy5. However, a similar study using recognize that genes have some influence been performed. Nor have these changes the same methods with German judges failed on behaviour, along with a host of other been directly linked to violent and other to replicate even this modest reduction7. factors, but not see that as incompatible antisocial behaviour. At best, then, we are a Another program of research, using large, with an expectation that people will long way from having the kind of evidence representative samples of the US population, exercise sufficient control to conform their that the law might find probative on issues systematically varied the heinousness of the behaviour to the law, even if for some people of responsibility and punishment. crimes/behaviours, the presence or absence that may require more effort than for others. of behavioural genetic evidence, and other Whatever the reason, and a combination What the future holds factors related to characteristics of the of factors may be at play, most people are Given the doctrinal and empirical challenges defendant, and asked participants to render unpersuaded that evidence regarding the to the effective use of behavioural genetic a variety of decisions (including whether a role of biological factors such as genes evidence for mitigation, we question the criminal defendant was guilty or not guilty should alter their decisions about consensus of most commentators that by reason of insanity; whether the defendant criminal punishment. the presence of such evidence in court should be sentenced to death; and what the In rejecting behavioural genetic proceedings will continue to grow, at least length of incarceration should be)8. Across evidence as a basis to reduce culpability and for the foreseeable future. To be sure, eight separate experiments, behavioural punishment, judges and lay people appear defendants facing the death penalty or long genetic evidence had no effect one way or to be in agreement with a group of scholars prison terms have little to lose by mustering another on perceptions of responsibility, who have argued that genetic explanations of every argument that could possibly have a nor on the degree to which individuals behaviour should have only a limited effect mitigating effect. In addition, genetic and should be punished for misbehaviour. on legal determinations of responsibility and other neuroscientific evidence is already However, the studies did consistently find punishment9. Demonstrating an increased being used to support claims of incapacity or that both the egregiousness of the behaviour risk for antisocial behaviour associated the presence of mental disorders. and the strength of participants’ beliefs with a particular genetic variant, they It should also be noted that potential in free will increased the magnitude of argue, is an insufficient basis on which to use of behavioural genetic evidence is not the punishments they levied. This lack of predicate a claim of reduced responsibility. limited solely to criminal trials. Employers effect is consistent with research failing The law traditionally has required the contesting claims that mental disorders to find consistent impact on culpability presence of either decreased rationality or are work related, civil litigants rebutting judgements of neuroscientific explanations impaired ability to control behaviour as arguments that their behaviour caused a of misbehaviour — typically based on an indicator of diminished responsibility. plaintiff’s emotional distress, or parties interpretations of fMRI data. Only if a genetic variant acts through one involved with child custody disputes, all Thus, for all the potential that some of these mechanisms, these scholars argue, might believe that behavioural genetic legal commentators and others have seen and produces a substantial decrement in evidence is potentially helpful to their case. in the use of behavioural genetic evidence rationality or behavioural control, should Indeed, civil defendants may attempt to in support of arguments for diminished the law take it into account in assigning compel complainants to undergo genetic responsibility and thus mitigation of blame and apportioning punishment. So testing to corroborate their claims. punishment, such effects have been difficult far, behavioural genetic evidence generally However, unless the introduction of to detect in actual cases — with rare has failed this test, and hence the impact of behavioural genetic evidence can be shown exceptions — and are modest or entirely behavioural genetic evidence on claims for materially to affect the outcome of cases, its absent in the experimental data. mitigation has, understandably, been weak. role in the legal process is likely to diminish.
Nature Human Behaviour | VOL 1 | NOVEMBER 2017 | 772–774 | www.nature.com/nathumbehav 773 © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. comment
If legal decision-makers — whether juries control. Until that happens — and a Published online: 18 September 2017 or judges — are unlikely to be swayed by sufficient body of evidence is not likely to DOI: 10.1038/s41562-017-0212-4 genetic evidence, there would seem to appear soon — the wisdom of the general be little reason for courts to fund genetic public may be worth attending to: resisting References 1. Denno, D. W. Mich. S. L. Rev. 967, 968–1047 (2011). testing for indigent defendants, or for them the allure of science may result in fairer 2. Baum, M. L. Neuroethics 6, 287–306 (2013). to overturn the convictions or sentences outcomes all around. ❐ 3. Byrd, A. L. & Manuck, S. B. Biol. Psych. 75, 9–17 (2014). of defendants who contend that their 4. Caspi, A. et al. Science 297, 851–854 (2002). 1 2 5. Aspinwall, L. G., Brown, T. R. & Tabery, J. Science 337, legal counsel was ineffective by failing to Nicholas Scurich * and Paul S. Appelbaum * 846–849 (2012). introduce evidence regarding the genetic 1Department of Psychology & Social Behaviour, 6. Feresin, E. Italian court reduces murder sentence based influences on their behaviour. Department of Criminology, Law & Society, on neuroimaging data. Nature News Blog http://go.nature. com/2vAykX0 (2011). Greater legal impact of genetic University of California, Irvine, 4213 Social and 7. Fuss, J., Dressing, H. & Briken, P. J. Med. Genet. 52, 1–8 (2015). explanations of behaviour, in turn, may Behavioural Sciences Gateway, Irvine, CA 92697- 8. Scurich, N. & Appelbaum, P. J. L. Biosci. 3, 140–157 (2016). await elucidation of the mechanisms 7085, USA. 2Department of Psychiatry, Columbia 9. Morse, S. J. Trends Cognit. Sci. 15, 378–380 (2011). 10. Buckholtz, J. W. & Meyer-Lindenberg, A. Bioprediction, associated with increased risk of antisocial University College of Physicians & Surgeons, NY Biomarkers and Bad Behavior (Oxford Univ. Press, Oxford, 2014). outcomes and demonstration of their State Psychiatric Institute, 1051 Riverside Drive, relationship to the traditional legal Unit 122, New York, NY 10032, USA. Competing interests standards of rationality and behavioural *e-mail: [email protected]; [email protected] The authors declare no competing financial interests.
774 Nature Human Behaviour | VOL 1 | NOVEMBER 2017 | 772–774 | www.nature.com/nathumbehav © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.