Species

Phylogenetic Species Concepts 249

which is de Queiroz’s later conception of a cohesive object or group over phylogeny.^38

The actual answer of the earlier paper, however, is that there is no single definition

of species that will “answer to the needs of all biologists and will be applicable to all

organisms,”^39 although they reject the sort of pluralism I proposed in 2003.^40

Autapomorphic Species....................................................................

Diagnosis of species has always been involved in the debate, but few if any have until

recently suggested that diagnosis is sufficient, apart from (and probably not even

there) the so-called Taxonomic Species Concept. Cronquist provided one of the first

such conceptions:

Species are the smallest groups that are consistently and persistently distinct, and dis-

tinguishable by ordinary means.^41

Some accused Cronquist of presenting a “subjective” concept,^42 but it all hinges

on what “ordinary means” means. At one time, the use of a microscope was reviled

(e.g., by Linnaeus); now assays for specificity ranging from molecular data to mor-

phometric and acoustic traits are considered ordinary practice.

More common phylogenetic diagnostic concepts, though, arise from the recogni-

tion that what makes taxa distinct are their apomorphies (or instead, their unique

sets of characters; apomorphies are usually single characters, not sets of characters).

Species have diagnostic autapomorphies—that is to say, they have unique constella-

tions of characters—while higher taxa (clades) have synapomorphies—shared con-

stellations of characters, which group them together. One instance of this approach

is found in the work of Donn Rosen:

... a geographically constrained group of individuals with some unique apomorphous

characters, is the unit of evolutionary significance.^43

In his paper on Guatemalan fishes, Rosen defined species in terms of individuals

and populations:

... a species is merely a population or group of populations defined by one or more

apomorphous features; it is also the smallest natural aggregation of individuals with

a specifiable genographic integrity that cannot be defined by any set of analytic

techniques.^44

(^38) de Queiroz 1998, 1999.
(^39) Quoting Kitcher 1984, 309.
(^40) Wilkins 2003.
(^41) Cronquist 1978, 3.
(^42) For example, Ghiselin 1997, 106f.
(^43) Rosen 1978, 176 quoted in Wheeler and Meier 2000, 55.
(^44) Rosen 1979, 277 quoted in Mayr 2000, 99.