Because it laid the foundation for nearly all subsequent epistemologies, Immanuel Kant’s Critique of Pure Reason has overshadowed his other interests in natural history and the life sciences, which scholars have long considered as separate from his rigorous theoretical philosophy until now. This book draws a link between these spheres by showing how the concept of epigenesis—a radical theory of biological formation—lies at the heart of Kant’s conception of reason. As the book argues, epigenesis was not simply a metaphor for Kant but centrally guided his critical philosophy, especially the relationship between reason and the categories of understanding. Offsetting a study of Kant’s highly technical theory of cognition with a mixture of intellectual history and biography, the book situates the epigenesis of reason within broader investigations into theories of generation, genealogy, and classification, and against later writers and thinkers such as Goethe and Darwin. Distilling vast amounts of research on the scientific literature of the time, it offers a look not only at Kant’s famous first Critique but at the history of philosophy and the life sciences as well.