Species

280 Species

of evolution, and asexual taxa—forms, morphs, types, niche occupiers, whatever—are

the outcome of evolution, then we need to be able to justify the special status of taxo-

nomic units like species over other taxonomic units. Simple familiarity through tradition

and acquaintance in one domain of biology is insufficient—zoological hegemony has

been a tendency in evolutionary and taxonomic theory for most of the twentieth cen-

tury. In part, the species problem arises because categorical concepts that applied well in

zoology failed to generalize outside it, or even those that applied well to some particular

group such as birds, mammals, or insects failed to generalize even to other animals, let

alone plants, fungi, lichens, algae, and so on. Perhaps, some commentators—both biolo-

gists and philosophers—suggest, the term “species” is a trashcan categorical and should

be replaced altogether. At least one major group of polychaete worms has been described

recently without mention of species, except to explain why species are not mentioned.

Perhaps “taxon” is sufficient. This will be discussed in Chapter 15.

Monism versus Pluralism

Philosophers of biology, along with biologists themselves, have divided into two
broad camps: monists about species concepts, and pluralists. Monists hold that
there is one conception of species that is correct; pluralists that there are many.
Philosophers may be monists or pluralists about a metaphysical view of species as
well as about which particular conception of biological species it is right to adopt and
champion. David Hull set up the philosophical species concept debate:

One reason why philosophers find the monism-pluralism debate so interesting is its

apparent connection to the dispute over realism and antirealism. Of the four possible

combinations of these philosophical positions, two seem quite natural: monism com-

bined with realism, and pluralism combined with antirealism. ... The other two com-

binations ... are somewhat strained. It would seem a bit strange to argue that one and

only one way exists to divide up the world, but that groups of natural phenomena pro-

duced on this conceptualisation are not ‘‘real.’’ They are as real as anything can get! ...

A combination of pluralism and realism seems equally peculiar. ... The world can be

divided up into kinds in numerous different ways, and the results are all equally real!^13

So Hull identified four philosophical options (Table 12.1) and argued that pluralist
realism is untenable. A great many philosophers followed him in this.
Given that few now think that there is one universal species conception, many have
argued for pluralist antirealism. Antirealism comes in two kinds: either there simply
are no such things as species (ontic antirealism) or there is no such category of “spe-
cies” that will suffice to capture the complexity of the living world (epistemic antireal-
ism). The latter view ties in with the commensurability issue mentioned above.
However, neither monist realism nor pluralist realism are incoherent. If there is
one kind of species, anything not covered by this category is simply not a species, no
matter what else it may be (a population, a type, a subspecific clade, or an agamospe-
cies). This would be the view of Mayr and Simpson, as discussed above. Moreover,
pluralist realism is not unknown either. Kitcher stated:

(^13) Hull 1999, 25.