The scope and significance of cytoplasmic inheritance has been the subject of one of the longest controversies in the history of genetics. In the first major book on the history of this subject, Jan Sapp analyses the persistent attempts of investigators of non-Mendelian inheritance to establish their claims in the face of strong resistance from nucleo-centric geneticists and classical neo-Darwinians. A new perspective on the history of genetics is offered as he explores the conflicts which have shaped theoretical thinking about heredity and evolution throughout the century: materialism vs. vitalism, reductionism vs. holism, preformation vs. epigenesis, neo-Darwinism vs. new-Lamarckism, and gradualism vs. saltationism. In so doing, Sapp highlights competitive struggles for power among individuals and disciplinary groups. He accepts that political interests and general social contexts may directly affect scientific ideas, but develops the stronger thesis that social interests inside science itself are always involved in the content of scientific knowledge. He goes on to show that there are no neutral judges in scientific controversies and investigates the social strategies and methodological rhetoric used by scientists when they defend or oppose a particular theory. At the same time, Sapp illustrates the social constraints that ensure the high cost and risk of entertaining unorthodox theories in the sciences.