Many decisions in the legal system and elsewhere depend on predictions of bad behaviors, including crimes and mental illnesses. Some scientists have suggested recently that these predictions can become more accurate and useful if they are based in part on biological information, such as brain structure and function, genes, and hormones. The prospect of such bioprediction, however, raises serious concerns about errors and injustice. Can biological information significantly increase the accuracy of predictions of bad behavior? Will innocent or harmless people be mistakenly treated as if they...