Though modern philosophers of science recognize the inappropriateness of the reduction of all scientific investigations to mathematics, mathematics and science share a long history with one another during which mathematics has been employed as a major component of scientific argumentation. Over the last twenty years, rhetoricians have done substantial work studying the role of argumentation in science (Bazerman 1988; Gross 1990, 2002; Myers 1990; Fahnestock 1999); however, despite the importance of mathematics in making scientific arguments, little effort has been made to understand the role mathematics has played in making these arguments. This dissertation represents a move to resolve this shortcoming by investigating the role of mathematics in arguments in evolutionary biology from the middle of the nineteenth to the beginning of the twentieth century.

In the first part of the nineteenth century, the mass collection and mathematical assessment of data for scientific purposes provides the context for understanding some of the rhetorical choices of an important group of natural philosophers and biologists who developed arguments in the second half of the century about the nature of variation, evolution, and heredity. In the works of Charles Darwin, Gregor Mendel, Francis Galton, and Karl Pearson, arguments from probability and statistics play important roles as support for their arguments and as a source of invention for their claims.

This investigation of the rhetorical situations of these four biologists, their arguments, and the role of the principles, operations, and formulae of probability and statistics supports the position that mathematization had a major impact on the nature of scientific evidence in the nineteenth century. What it also suggests is that, though mathematized arguments may have had a great deal of credibility within the scientific community in general, factors such as the stature of the rhetor and of their biological theory within their specific discourse communities played an equally important role in the persuasiveness of their arguments.