Abstract

Traditionally, species have been treated by biologists and philosophers as natural kinds. However, this conception of species has posed several problems for evolutionary theory. For example, biologists have been hard pressed to find traits had by all and only the members of a species. This has caused some philosophers to doubt that evolutionary theory is a scientific theory. ;In an effort to resolve such problems, Michael Ghiselin and David Hull have argued that species are not kinds but individuals. A number of authors have adopted this conclusion. Some have even gone on to argue that besides showing that species are not kinds, the thesis that species are individuals has other ramifications for evolutionary theory. For example, the thesis is said to lend support to the Theory of Punctuated Equilibrium. ;In my dissertation, I argue that while species are not kinds, most species are not individuals either. Furthermore, even if all species were individuals, the alleged ramifications are not forthcoming. ;More specifically, in Chapter One I review the arguments against species being kinds and the recent replies to those arguments. I also examine the nature of kinds and contend that the original arguments against species being kinds still stand. ;In Chapter Two, I turn to the metaphysics of individuality. I argue that mere spatiotemporal continuity and a rough similarity among the constituents of an entity are insufficient for it to be an individual. The constituents of an individual must be appropriately causally connected as well. ;With this requirement, I return to species in Chapter Three. Most species consist of subpopulations which are not causally connected in any biological fashion. Because of this, and other reasons, I argue that most species are not individuals. ;In the final chapter, I point out that the result of the previous chapter goes against the claim that what distinguishes species from higher taxa is that species and not higher taxa are individuals. I also argue that even if all species were individuals, their individuality does not support the Theory of Punctuated Equilibrium. Finally, some authors maintain that a unit of selection must be an individual. I argue that there is no such requirement on units of selection