Species, Taxonomy, and Systematics 415genetic standards for being cohesive evolutionary units. Mishler and Brandon’s
pluralism leaves out a significant kind of basal lineage on the tree of life.
3.3 Monist Responses
Needless to say, monists are not happy with pluralism. They offer many responses
to species pluralism. One objection is that pluralism is an overly liberal approach
to science [Sober, 1984; Ghiselin, 1987; Hull, 1987; 1999]. Hull and others ask
how pluralists determine which species concepts, among the plurality of suggested
concepts, should be accepted as legitimate. Should any concept proposed by a
biologist be accepted? If pluralism offers no criteria for discerning among species
concepts, then pluralism, according to Hull [1987], boils down to the position of
‘anything goes.’
Ereshefsky [1992] and Dupr ́e [1993] respond to this objection by suggesting cri-
teria for accepting a proposed species concept. Those criteria are such epistemic
virtues as empirical testability, internal consistency, and intertheorectic consis-
tency. These are standard epistemic virtues that scientists and philosophers use
for judging theories. In judging a species concept, one might ask, for example,
if the concept’s theoretical assumptions are testable. BSC, for instance, assumes
that interbreeding is an important factor in maintaining the existence of stable
groups of organisms. Whether interbreeding causes such stability is empirically
testable, and biologists do test that hypothesis in the field and in the lab [Tem-
pleton, 1989]. Pluralists do not subscribe to a position of ‘anything goes.’ Species
pluralists believe that legitimate species concepts must meet specific epistemic
standards.
A recent response to species pluralism is that all well-accepted species concepts
are captured by a more inclusive species concept. De Queiroz [1999] and Mayden
[2002] observe that all prominent concepts assume that species taxa are lineages.
Consequently, de Queiroz and Mayden offer a Lineage Concept of Species that,
according to Mayden [2002, 191], “serves as the logical and fundamental over-
arching conceptualization of what scientists hope to discover in nature behaving
as species. As such, this concept... can be argued to serve as the primary concept
of diversity.” De Queiroz and Mayden believe that the species concepts currently
accepted describe different types of species lineages — for example, interbreeding
lineages, ecological lineages, and phylogenetic lineages, and the Lineage Species
Concept provides the proper account of all species lineages. De Queiroz and May-
den believe that their species concept is a monist answer to pluralism because it
provides the one correct account of species.
A problem with de Queiroz and Mayden’s Lineage Species Concept is that it fails
to highlight a unique group of entities that should be called ‘species.’ Recall that
Mayden believes that the Lineage Species Concept captures that “over-arching
conceptualization of what scientists hope to discover in nature behaving as species”
(ibid.). Such a conceptualization should capture what is common anduniqueto all
species taxa. Interbreeding, ecological, and phylogenetic species are all lineages,