Abstract

Population geneticists investigate the conditions for the possibility of evolution. They use mathematical models to describe how natural selection, mutation, migration, and drift may change the genetic constitution of populations of organisms. As such, population genetics serves as the theoretical core of evolutionary biology. This dissertation investigates the conditions for the possibility of population genetics. A history of the conceptual and empirical origins of the discipline is followed by an examination the work of R. A. Fisher and Sewall Wright, two key figures in the history of the discipline. My aim is to gain a better philosophical understanding of the role of mathematical models in biological theory and explanation. ;Only recently have philosophers turned to the study of evolutionary biology as an exemplar of scientific theory and practice. My work differs from much of this recent work in being historical. By examining one particular episode in the history of evolutionary biology, I uncover the different ways in which theoretical population geneticists use models, different aims of scientific explanation, and whether and in what sense it is appropriate to say that evolutionary biology is "unified" or provides "unifying" explanations. ;Morrison has recently claimed that while Fisher and Wright gave us a unified mathematical theory, they offered competing explanations of evolution in populations. She uses this alleged disunity at the level of explanation combined with unity at the level of the mathematical theory to make a case that unification and explanation are often at odds in science. Morrison's assessment rests on two, related assumptions: first, that all explanations are causal, and second, that mathematical theories are not explanatory to the extent that they "leave out the causes." I defend a pluralistic and pragmatic conception of explanation according to which mathematical models may explain, even when they do not provide the causal machinery behind some process. I argue that standard approaches to explanation, and relatedly, to the structure of theory and the role of models in science, need serious reconsideration. There is a diversity of types of understanding sought in the sciences; and in parallel, there is a diversity of types of explanation