When Certainty Dissolves into Probability: A Legal Vision of Toxic Causation for the Post-Genomic Era

Table of ContentsI. Introduction 239II. The Persistent Problem: Toxic Injury and the Traditional Deterministic Model of Causation 241A. The Traditional, Deterministic Model of Causation 241B. The Lack of Fit in Toxic Injury Cases 244III. Solutions Illusory and Real: The False - and True - Promise of Genomics 252A. A Bit of Genomics 2531. Genes and Disease 2542. Toxic Exposure and Disease - and Genes 2573. The Tools of Toxicogenomics 259B. The False Promise 265C. The True Promise and Its Implications 276TV. An Alternative Vision: Probabilistic Causal Contribution 281A. A Metaphor 282B. Contributing Factor Causation 284C. Risk as Cause, Not as Harm 297D. The Question of Substantiality 304E. Discounted Recoveries 307F. Boundaries 319V. Probabilistic Causal Contribution and Tort Goals 322A. Deterrence Goals: Is Probabilistic Precision Probable? 322B. Corrective Justice Goals: Is Causation Different? 330C. Truth-seeking Goals: Wrong All the Time? 336D. Administration of Justice Concerns: Too Much Information? 337VI. Conclusion 338/. IntroductionForty years after a jury first found that several asbestos product manufacturers each had caused someone's asbestosis and pleural mesothelioma,1 sick people continue to come to court seeking compensation for illnesses that they allege were caused by exposure to various toxins. The defendants sued for making, selling, using, or disposing of the allegedly toxic products continue to protest that something else - dumb luck, bad genes, someone else's similar product, some entirely different toxin, or mother nature - is what really made the plaintiffs sick, and, more important, that the plaintiffs cannot prove otherwise.Proof of toxic tort claims conforms poorly to the traditional deterministic legal model of but-for causation, because toxic injuries almost never involve an observable chain of physical events allowing easy inference of a causal relation between a particular defendant's conduct and a particular plaintiffs harm. Courts turn to science to replace causal intuition, but a disjunction remains between the probabilities that science can know and the determined result that the law wants proven. The resulting problem has produced hundreds of court opinions and numerous calls for doctrinal reforms in recognition of the difficulties that toxic causation presents. Yet, despite decades of thoughtful jurisprudence and scholarship, the core legal conception of toxic causation has hardly changed at all.Science has changed, however, quickly and at an accelerating pace. The ability to peer into the genome heralds new insights into human susceptibility to toxic substances. Molecular technologies provide glimpses of previously inaccessible toxic mechanisms. Computing power allows this research to be conducted on a scale and at a rate never before possible.The law looks to this new science, hoping that its increased resolving power will at last build a bridge from probability to certainty. The dream is that genomic knowledge will lead to deterministic proof of the existence or absence of causal mechanism in individual cases. That "holy grail" of particularistic evidence would at last eliminate much of the indeterminacy that has plagued proof of specific causation in toxic tort claims;2 it also could fatally undermine arguments for exceptional judicial treatment of toxic tort claims, restoring to tort law a universally applicable deterministic model of but-for causation. …