Proof of causation in toxic torts has presented persistent problems for the legal system, because the probabilities that science can know fit poorly with the demands for particularistic proof imposed by the law’s deterministic model of causation. Some scholars have hoped that genomic and molecular information will at last provide scientific certainty—definitive, individualized proof of toxic causation. This Article argues that the opposite is true. Scientific research will increasingly elucidate the ways in which environmental exposures and human genes interact to produce disease, but this deeper knowledge will extend rather than resolve the problem of causal indeterminacy in toxic torts. Genomic and molecular understanding, instead of sounding the death knell for proposals to reform toxic tort causation law, will strengthen the argument for those reforms. This Article proposes a probabilistic causal contribution model to replace the model of deterministic causation in toxic torts, building on earlier scholarly proposals and the creativity of a handful of courts. The Article explores how the model would work and argues that it is superior to present doctrine when assessed against the goals of the tort system.