Much recent thought on the ethics of new biomedical technologies, and work in ethics and political philosophy more generally, is committed to hidden and contestable views about the nature of biological reality. This selection of essays by Tim Lewens, a leading expert in the field, teases out these biological foundations of bioethical writing and subjects them to scrutiny. The topics covered include human enhancement, the risks of technical progress, the alleged moral threat of synthetic biology, the reality of human nature, the relevance of evolutionary psychology to social policy, the nature of the distinction between health and disease, and justice in healthcare decision-making.