Abstract

This dissertation explores the philosophical aspects of the recent debates over macroevolution . I focus particularly, but not exclusively, on models of species selection. ;In the first part of the dissertation I offer a limited defense of species selection, arguing that it does occur and responding to many of the most forceful objections raised against species selection. Following Brandon, I argue that selection occurs at the species level if the differential reproductive success of species is best explained in terms of their differential adaptedness to a common environment. Two of the prominent objections to species selection concern species individuality and the species-level selective environment. In order to be selected, species must be "cohesive wholes." I maintain that at least some species are cohesive with respect to the process of selection because they have properties that affect their fitnesses. Regarding the environment, I argue that if one individuates species-level environments with respect to species-level fitnesses, species often do occupy common selective environments. ;In the second part of the dissertation I provide two further grounds for accepting a non-reductionistic evolutionary theory. First, even if species selection never occurs, effect macroevolution cannot always be explained by the synthetic theory. Second, the methodological reductionism of the synthetic theory fails in two ways. Because different evolutionary patterns emerge at different levels, an accurate description of macroevolutionary phenomena requires attention to the hierarchical organization of life. Because some phenomena can be correctly described and explained by models at two different levels and because the higher-level models can provide new insights, we are not methodologically compelled to prefer lower-level accounts. This version of explanatory pluralism suggests a non-reductionistic account of the unity of science: both the higher- and lower-level models provide different but correct perspectives on the evolutionary process. Because I advocate the continued use of lower-level models, my account is non reductionistic