There is a paradox lying at the heart of the study of heredity. To understand the ways in which features are passed down from one generation to the next, we have to dig deeper and deeper into the ultimate nature of things - from organisms, to genes, to molecules. And yet as we do this, increasingly we find we are out of focus with our subjects. What has any of this to do with the living, breathing organisms with which we started? Organisms are living. Molecules are not. How do we relate one to the other? In Genetic Analysis, one of the most important empirical scientists in the field in the twentieth century attempts, through a study of history and drawing on his own vast experience as a practitioner, to face this paradox head-on. His book offers a deep and innovative understanding of our ways of thinking about heredity.