Abstract
Monism versus pluralism about biological species concepts remains contested terrain in the life sciences. Monists countenance one species concept. Pluralists embrace several. I reject three main schools of monistic species concepts and endorse a broadly evolutionary species concept using thin adequacy criteria. I then distinguish two species of pluralism based on their response to the cross-classification problem: is there a uniquely correct scheme for grouping biological organisms? Chaste pluralists reject cross-classificationism whereas promiscuous pluralists embrace it. Deciding between chaste and promiscuous pluralisms hinges on the frequency of "messy situations" in taxonomy. Using the adequacy conditions and considering the frequency of messy situations, I argue against the promiscuous pluralisms of Dupré, Kitcher, and Ereshefsky, against Ruse's chaste pluralism, and in favor of a moderately chaste pluralism. I argue that we must distinguish global and local varieties of promiscuous pluralism and chaste pluralism, and that a novel "hybrid pluralism" comprised of local chaste and local promiscuous pluralisms may be the most reasonable general conclusion to draw or at least a viable alternative to global promiscuous pluralism. Lastly, I sketch the relationship between the different forms of species pluralism and realism about biological species and argue that chaste pluralisms are compatible with species realism whereas promiscuous pluralisms are not, which may speak in favor of chaste pluralism considering species' explanatory role in the life sciences.