This paper concerns the relationship between species pluralism and the species category. It is customary to disambiguate `species' into the species category and species taxa. Species taxa are whatever different species names refer to, e.g., Castor canadensis; the species category is the class to which all the different species taxa belong. It's not clear how profitable this distinction has been, nor is it clear if there is confusion by the ambiguity between these two uses. However, due in part to this disambiguation, there is a concern about species pluralism and the species category, which as I argue, is not the main burden of pluralism.
To show that there is more to pluralism than this concern, I compare it with monism and relativism. Monists take species concepts as definitions of the species category. Pluralists can't, because they accept more than one species concept. There are four pluralist strategies: (1) Eliminativism (Ereshefsky, 1992, 2001); (2) Disjunctivism (Pigliucci, 2003, 2005); (3) Minimalism (de Queiroz, 1998, 1999, 2005a, 2007); (4) Pragmatism (de Queiroz and Donoghue, 1988; Dupre, 1999; Ereshefsky, 2014). My aim is to show how these solutions aim to resolve apparent conflict between pluralism and biological theory, but fail to treat important aspects of biological practice, like the consilience that obtains between some competing species concepts.
Eliminativists argue that if pluralism is true, then it implies that the species category is empty. If the species category is empty, then we should eliminate it from scientific discourse (Ereshefsky, 1992, 2001). After surveying common problems with eliminativism (Brigandt, 2003), I show that the biggest problem the view faces comes from biological practice: many species are named as such by way of congruence between many species concepts. Some have interpreted this use of species concepts as reason to conclude that different species concepts, by way of consilience, will ultimately classify organisms in a single way (Ruse, 1987). However, as I argue, a pluralist can accept a certain degree of consilience without resorting to monism. However,a pluralist must do this without eliminativism.
Disjunctivists argue that pluralism only implies that the species category is undefinnable in the traditional sense (Scriven, 1959; Hull, 1965; Pigliucci, 2003, 2005). I argue that the problem with disjunctivism is that these sorts of definitions often say nothing about when something satisfies multiple conditions. That is, whether or not a degree of consilience lends more support to claims about whether or not this or that group is a species. As it stands, most disjunctive definitions of the species category do nothing other than combine the available species concepts in a disjunctive fashion. And what may be worse is that "Rather than resolving the incompatibilities among alternative definitions of the species category, this interpretation encourages different authors to adopt incompatible definitions, thus perpetuating the current disagreements" (de Queiroz, 2005a, 1266). I argue that disjunctivism needs to be reformulated with the relationships between different admissible species concepts in mind.
Minimalists give up the quest for a operationalizeable definition of the species category, but require that it be universal and unified (de Queiroz, 1998, 1999, 2005a,b, 2007; Mayden, 1997, 1999; Shun-Ichiro, 2011; Kendig, 2014). Minimalism is thus sensu strictu a sophisticated monism. After looking at several minimalist attempts to accommodate pluralist concerns about species concepts, I argue that minimalism leads to pluralism about the entities by which we define species. If we define species as separately evolving metapopulation lineages, this leads
to pluralism about metapopulation lineages (de Queiroz, 2005a; Haber, 2012). Thus, disjunctivism and minimalism are highly compatible with one another. The difference is that they put the pluralism, as interpreted disjunctively and not eliminatively, in different places (cf. Hull, 1999). I then consider a further objection that minimalism is too permissive (Pigliucci, 2003; Ereshefsky, 2014). One way of countering this objection is to bite the bullet, and argue for an analogy between the traditional notion of species and a permissive minimalism, and the traditional notions of organism as focused on the adult with our modern more permissive understanding of organism (de Queiroz, 1998, 1999). I argue that this strategy fails, because it con icts with current biological practice.
The last solution to species pluralism and the species category problem is to argue for pragmatic constraints. Even if species pluralism is true, past species delineations should be preserved (de Queiroz and Donoghue, 1988;
Dupre, 1999; Ereshefsky, 2014). A common problem with the solutions thus far considered concerns the extent to which they would affect biological practice. Reflecting on this has caused many initially revolutionary pluralists to gravitate toward pragmatism. Some have argued that accepting pluralism will `lead to Babel' (Ghiselin, 1969, 1997; Hull, 1987, 1989). This is also known as the communication objection to pluralism (Ereshefsky, 1992, 680-681). I argue that these monists are exaggerating the consequences of accepting pluralism (Kitcher, 1984, 327).
"Species" plays too many roles in too many disciplines for it to be changed in any significant way, let alone eliminated from discourse (Dupre, 1999; Ereshefsky, 2014). Pragmatism is much weaker than either minimalism or disjunctivism. I argue that it really tells us nothing about what to do with the conceptual pluralism that has run rampant in biology, other than that we should just continue in the face of it. In effect, it is rather worrisome, because it, of all the positions so far considered, is closest to relativism or cynicism (Kitcher, 1984, 308). Further, pragmatism is compatible with all the different forms of pluralism we have already considered. This again is the general problem with species pluralists solely focusing on the species category problem.
I close this paper by raising two independent questions about the relationship between pluralism and species concepts that are independent of what pluralism implies about the species category problem. First, which species concepts are admitted as legitimate? Second, how do those that remain work in relation to one another? I will explore the ways in which the different forms of species pluralism answer these two questions, especially focusing on the distinction between evolutionary and extra-evolutionary species pluralism.