 Philosophy of biology can also be subdivided by the particular areas of biology with which it is concerned. Until recently, evolutionary biology has attracted the lion’s share of philosophical attention. This work has sometimes been designed to support a general thesis in the philosophy of science, such as the “semantic view” or model-based view of theories (Beatty 1980; Lloyd 1988; Thompson 1988). But most of this work is concerned with conceptual problems that arise inside the theory itself, and the work often resembles theoretical biology as much as pure philosophy of science. For example, Elliott Sober’s classic study The Nature of Selection: Evolutionary Theory in Philosophical Focus (Sober 1984b) marks the point at which many philosophers became aware of the philosophy of biology. Sober analyzed the structure of population genetics via an analogy with Newtonian mechanics and the composition of forces, treating the actual change in gene frequencies over time as the result of several different “forces”, such as selection, random genetic drift, mutation, and migration. Several philosophers of biology have challenged this interpretation of evolutionary theory in favor of a “statistical” approach (Sterelny &amp; Kitcher 1988; Matthen and Ariew 2002; Walsh, Lewens, and Ariew 2002), and this debate continues. Another instance of a conceptual problem in evolutionary theory concerns the nature of random genetic drift. How are selection and drift distinct (Beatty 1987)? We typically think of drift occurring when there is random fluctuation of gene frequencies, but selection in a changing environment can produce the very same pattern. Thus, some philosophers of biology have argued we must distinguish selection and drift as processes rather than just as patterns. One way to do this is through a distinction between indiscriminate and discriminate sampling processes (Millstein 2002; Brandon 2005; Millstein 2005). The question becomes whether the trait of interest is causally irrelevant or relevant to changes in gene frequencies. These examples of careful, methodological analysis of population genetics, the mathematical core of traditional evolutionary theory, continue to give rise to interesting results (Pigliucci and Kaplan 2006; Plutynski 2006; Okasha 2007; Sarkar 2011).