Stephen Jay Gould, 1973,
Ever Since Darwin.
THE PROBLEM OF SUBSPECIES
According to Stebbins and Wake, Ensatina eschscholtzii has been subdivided into seven subspecies (eschscholtzii, xanthoptica, oregonensis, platensis, croceater, and klauberi). The use of a taxonomic category called “subspecies” has been questioned by Gould 1973 and others.
Gould quotes Mayr (1942) stating that
“The subspecies, or geographic race, is a geographically localized subdivision of the species, which differs genetically and taxonomically from other subdivisions of the species.”
Gould goes on to say:
“We need to satisfy two criteria: (1) a subspecies must be recognizable by features of its morphology, physiology, or behavior, that is, it must be ‘taxonomically’ (and by inference, genetically) different genetically from other subspecies; and (2) A subspecies must occupy a subdivision of the total geographic range of the species.When we decide to characterize variation within a species by establishing subspecies, we partition a spectrum of variation into discrete packages with distinct geographic borders and recognizable traits.
The subspecies differs from all other categories in two fundamental ways: (1) Its boundaries can never be fixed and definite because, by definition, a member of one subspecies can interbreed with members of any other subspecies in its species (a group that cannot breed with other closely related forms must be designated a a full species); (2) The category need not be used.”
Gould also states that
“The subspecies is a category of convenience. We use it only when we judge that our understanding of variability will be increased by establishing discrete, geographically bounded packages within a species. Many biologists are now arguing that it is not only inconvenient, but also downright misleading, to impose a formal nomenclature on the dynamic patterns of variability that we observe in nature.”
With Ensatina, the various subspecies show that they interbreed from one to the next around the state of California except the southernmost extremes of their distribution. There in the mountains east of San Diego, the two southermost subspecies eschscholtzii and klauberi have been shown to be totally reproductively isolated in the Cuyamaca Mountains, but only partially isolated in the Palomar Mountains (See Devitt research). I argue that dividing Ensatina eschscholtzii into seven subspecies is not misleading, but to the contrary, subspecies of of Ensatina clarifies the evolutionary relationships among the various populations. According to Wake and Schneider, 1998:
“We prefer a taxonomy that clarifies the evolutionary relationships among the components and that highlights, rather than obscures, the complex interactions of the past and the present.”(See the problem defining the term "species")