Genetics and Responsibility: To Know the Criminal From the Crime

I understand by responsibility nothing more than actual liability to legal punishment. It is common to discuss this subject as if the law itself depended upon the result of discussions as to the freedom of the will, the origin of moral distinctions, and the nature of conscience. Such discussions cannot be altogether avoided, but in legal inquiries they ought be noticed principally in order to show that the law does not really depend upon them. (1) I INTRODUCTION Human behavioral genetics may enhance our understanding of human behavior and yet have little relevance to assigning responsibility in the criminal law. As a scientific discipline, behavioral genetics seeks to understand the contributory roles of genetics and the environment to observed variations in human behavior. Like other sciences, it assumes that all natural phenomena have a scientific causal explanation, but focuses primarily on the correlation between genetic variation and behavioral variation among individuals in a population. Although the science is still in its infancy, stymied by disagreement over basic methodology and the definitions and metrics for measuring behavior, behavioral genetics evidence has already been introduced in criminal trials for a variety of purposes: as exculpatory evidence, to bolster preexisting legal defenses, and as mitigating evidence during sentencing. As the science progresses and gains credibility, scientific results demonstrating a genetic contribution to behavioral differences in violence, aggression, hyperactivity, impulsivity, drug and alcohol abuse, antisocial personality disorder, and other related traits will continue to be introduced into the criminal law. This article discusses practitioners' attempts to use behavioral genetics evidence in U.S. criminal law cases, and explores the relationship between behavioral genetics and the theoretical concept of criminal responsibility as it operates in the U.S. criminal justice system. It argues that irrespective of the scientific progress in the field of behavioral genetics, as a matter of criminal law theory, such evidence has little utility in assessing criminal responsibility. Several observations about the science of behavioral genetics inform the arguments presented in this article. First, behavioral genetics does not support the perspective that human actions are fixed or caused by genes. In other words, behavioral genetics does not support genetic determinism. To the contrary, the science elucidates a complex interaction of biology and the environment that gives rise to behavioral differences between individuals. The conceptual conflict between behavioral genetics research and genetic determinism is evident both from the nature of the studies and from the scientific results. Second, studies in behavioral genetics are designed to generate a population statistic about the correlation between behavioral variation and genetic variation in a population, termed an estimate of "heritability." (2) Heritability provides a statistical approximation of the relative contribution of genetic differences versus environmental differences to observed behavioral differences among individuals in a population. (3) In contrast, it does not explain the relationship between the genetic profile of an individual and his behavior, nor does it explain the causes of any particular act by an individual. (4) As a population statistic, heritability may vary by the age, culture, and environment of the population under study. (5) Moreover, the old adage in statistics rings true here as well: correlation does not imply causation. A statistical correlation between genetic differences and behavioral variation in a population does not translate into a causal explanation about the behavior of interest. (6) In short, heritability does not explain the causes of an individual's behavior, or the causes of any specific act by an individual. (7) Third, behavioral genetics studies reveal that even if genetic differences provide insight into why individuals behave as they do, genetic differences contribute only one part to the overall story. …