Species

370 Appendix B

presented in Wheeler and Meier 2000 as well as Hausdorf 2011. I also add some “par-

tial” species concepts—the compilospecies concept and the nothospecies concept.

Conceptions with asterisks are what I consider to be “foundational” conceptions,

from which the others are constructed in whole or part.

Reproductive Isolation Conceptions (RISC)

Basing species on the ability of organisms to reproduce successfully is as old as nat-
ural history; as we have seen, Darwin considered (and rejected) it, as did Linnaeus
and many others. It is not even the sole biological conception. As Van Valen noted,
“The term ‘biological species concept’ is a propagandist ploy.”^3 Many have noted
that conceptions based on living things are always biological, and that this is better
called something like a reproductive species concept; hence my use of RISC.

Phylospecies (PSC)

In addition to Hennig’s conception (1950, 1966), I distinguish between two phylospe-

cies concepts that go by various names, mostly the names of the authors presenting

at the time, as in (Wheeler and Meier 2000). To remedy this terminological infla-

tion, I have christened them the autapomorphic species conception and the phyloge-

netic taxon species concept.^4 Asterisks identify the “primary” conceptions (Mayden

1997), from which the others are formed. Mayden has criticized several of these as

being insufficient for that purpose, but I have tagged those which seem to function as

primary conceptions in scientific practice, if not in philosophical terms.

Definition: The smallest unit appropriate for phylogenetic analysis, the smallest

biological entities that are diagnosable and monophyletic, unit product of natural

selection and descent. A geographically constrained group with one or more unique

apomorphies (autapomorphies).

There are two versions of this and they are not identical. One derives from Rosen

and is what I call the autapomorphic species conception [conception 2]. It is primar-

ily a concept of diagnosis and tends to be favored by the tradition known as pattern

cladism. The other is what I call the phylogenetic taxon species conception [concep-

tion 23], and tends to be favored by process cladists.

Principal Authors: Cracraft 1983, Eldredge and Cracraft 1980, Nelson and

Platnick 1981, Rosen 1979.

Synonyms: Autapomorphic phylospecies, monophyletic phylospecies, minimal

monophyletic units, monophyletic species, lineages.

Related Concepts: Similar to: internodal species cladospecies, composite species,

least inclusive taxonomic units.

(^3) Van Valen 1988, 54.
(^4) In the first edition, I called this the “synapomorphic” species conception.