Working with Dr. John Beatty of the University of Minnesota, Dr. Swetlitz is seeking to delineate the historical factors responsible for the public controversy between Julian Huxley and Theodosius Dobzhansky regarding the definition of "fitness" in the early 1960s. This controversy reflected important social factors shaping the meaning and defense of key concepts in post-World War II evolutionary biology: efforts by geneticists to distance "fitness" from eugenic considerations, the rise of population genetics as the central field in evolutionary biology, and reactions in opposition to both of these developments. This research will contribute to a number of areas of scholarship within the history and philosophy of biology including the growing literatures on the evolutionary synthesis, the relationship between genetics and society, and on Huxley and Dobzhansky in particular. It will also complement the philosophical literature by emphasizing the historical contingencies that affect how terms take on meaning.