The relationship between deterministic and random processes in the mechanisms of evolution in nature has been a fundamental feature of modern evolutionary biology since the early 1930's. The tension between Sewall Wright's and R. A. Fisher's views of mechanisms of evolution has been extremely important in shaping much of the theoretical and field work in evolutionary biology. This tension stems basically from their differing interpretations of the relative roles of deterministic selection and random genetic drift. In the period since 1950, the primary foci of interest in the tension between selectionist and neutralist interpretations have been in the controversies surrounding: 1) Ernst Mayr's concepts of founder effect and genetic revolution in speciation, 2) the selectionist interpretation of microevolution at the phenotypic level, represented by the Oxford School of ecological genetics, and 3) Motoo Kimura's neutral theory of molecular evolution. Under this grant, Professor Provine will examine in detail the two major schools at opposite ends of the spectrum in this debate: the Oxford School of ecological genetics and Motoo Kimura's neutral theory of molecular evolution. The first represents a deeply selectionist (i.e. deterministic) interpretation of evolution in nature and the second a deeply neutralist (i.e. random) interpretation. Professor Provine will also examine the history of the interplay between ideas about natural selection and random drift by focussing upon the controversy over Ernst Mayr's concepts. Finally, the study will trace the rise of attempts to synthesize neutralist and selectionist interpretations, in regard to both microevolution and macroevolution. This study promises greatly to enhance our understanding of how scientific theories develop, interact with their competitors, and finally themselves evolve in the scientific process of selection of the most viable explanation for natural phenomena. Thus the study will contribute to the history and philosophy of science as well as to the understanding of contemporary evolutionary thought.