The concept of heredity played a powerful role in structuring 19th-century debates over sickness, morality, class, race, education, social change and evolution. But there was very little agreement as to which qualities were heritable and how new hereditary variants were acquired. In consequence, notions of heredity existed in a wide variety of forms, expressing anything from extreme determinism and a belief in the incorrigibility of individuals, social and racial groups, to unleavened optimism, and a faith in ultimate human perfectibility. This article explores these rich hereditarian discourses to convey an impression of a century that was at least as preoccupied with the concept of biological inheritance as we are today.