I am gratified to find that ideas I published a few years ago in Life Science in the Twentieth Century have stimulated a controversy about some important issues in the history of biology. In the Introduction to that book I wrote, "If this book has any lasting merit . .. it will be less in the questions that it answers than in those it raises . . . The best history tries to phrase issues so . . . that others can go beyond and investigate them more thoroughly." This is exactly what Jane Maienschein, Ronald Rainger, and Keith Benson have done. I am glad they took me at my word and challenged ideas that, more than five years ago, I advanced as one way of organizing our thinking about the development of biology between roughly 1880 and 1930. The foregoing papers offer several valid criticisms of the basic thesis, I outlined in Life Science in the Twentieth Century (1975; 1978), Thomas Hunt Morgan: The Man and His Science (1978), and "Naturalists and Experimentalists: The Genotype and the Phenotype" (1979).' Simply stated, my argument is that American biology between about 1880 and 1930 witnessed a sharp, radical shift in methodology and the problems addressed. That shift proceeded from an interest in problems of phylogeny and natural history, pursued largely with descriptive methods, to an interest in problems of embryogenesis, heredity, and physico-chemical processes, pursued with analytical and experimental methods. The shift occurred because younger workers in the 1880s and 1 890s became tired of pursuing problems of phylogeny and of the endless speculations that seemed at the time to attend much of the work of nineteenth-century morphologists, including their own teachers. In a sense, younger biologists "revolted" against the problems pursued by and the methods espoused by older investigators. In breaking with the older tradition (often exemplified for younger workers by morphology),