The Gall Wasp Genus Cynips: A Study in the Origin of Species/The Taxonomic Method
THE TAXONOMIC METHOD
The attainment of sound ends in any field of science depends on certain common fundamentals of scientific method. An adequate understanding of any phenomenon must await repeated observations of that phenomenon thruout a wide range of specific cases, and an interpretation of the data based upon a comparative study of the groups in which that phenomenon is known to appear. It is only because the nature of the material studied and the categorical rank of the unit of comparison varies considerably with the problem under observation that we assign each biologic question to some special field, recognizing that each sub-science provides the best means of handling particular materials and particular categories.
To morphology, physiology, and psychology we make certain assignments not only because we wish to deal with particular aspects of the organic organization, but because these sciences are adapted for dealing with ordinarily few species which may be taken to stand as types of whole orders and classes or phyla of plants or animals. For this reason these sciences contribute data on such problems as the relationships of the larger groups, their appearance in the geologic record, and their value as evidence of the processes of evolution itself. In genetics, on the other hand, it is the individual which is the category chiefly concerned, and the correlations are made between individuals of experimentally proved hereditary relationships. In taxonomy the data are again individual organisms, but the comparisons employed are between such groups of individuals as constitute what we call species, and between all of the species for which we may find evidence of close, phylogenetic affinities. The unfolding of the complete record of evolution would thus appear to depend upon the coördination of the contributions from cytology, genetics, taxonomy, comparative anatomy, embryology, paleontology, and still other fields less particularly concerned with the problem; and it is with this appreciation of the magnitude of the whole species problem that we hold a brief for the taxonomic method as fundamental to the elucidation of certain aspects of the subject.
I take it that the essential function of the taxonomic method is this interpretation of biologic phenomena by the comparison of related species. Whenever taxonomists increase their data (individuals studied) to a volume comparable with that on which the best research in other fields has been based, pursue their comparisons of related species as persistently as the geneticists have compared related generations of individuals, and strive towards interpretations of their data which shall be coördinated with the findings from other fields of biology, we shall have a taxonomic science that cannot fail to command the respect of students. If taxonomy has been in ill repute, it is because we have considered as our chief function the solution of something other than biologic problems. Too many systematists attain their objectives when each species is "represented" by a half-dozen specimens pinned in their cabinets. These are the systematists responsible for the definition of systematic entomology as the science of transferring pins from one box to another. If taxonomists have too often made species-descriptions and catalogs and nomenclatorial inanities the end of their efforts, it is no proof that the science cannot rise above its technic and concern itself with biologic problems. As my good friend has remarked, our difference is not with taxonomy but with taxonomists.
It is, then, as something of a defense that I detail the several items of the taxonomic method and give a specific accounting of the basis for the present analyses of species in the genus Cynips.
I should detail the taxonomic method in the following items:
1. The validation of data and conclusions by the utilization of large series of individuals of each species.
2. The utilization of series from wide-spread localities fairly representative of the range of each species.
3. The utilization of such material for every one of the species constituting the natural group under investigation.
4. The recognition of relationships between individuals and species by the consideration of every character which may be shown to have hereditary significance, to wit: morphologic structures of any and every sort; such physiologic characteristics as can be shown to be hereditary and subject only to such environmental modifications as may be measurable; such special physiologic characteristics as are more often classified as psychologic, or as elements of “behavior”; and whatever other measure there may be of the physico-chemical organization which is the hereditary basis of the organism. This, in brief, demands a biologic as well as a structural basis for the recognition of species.
5. The special consideration of individual variation, with an attempt to analyze the hereditary or non-hereditary basis of the unusual characters. Many of the older workers made it a practice to throw their “exceptions” into the waste basket!
6. The accumulation of data with due scientific caution, and the further preservation of data in the form of labelled specimens, with the detailed citation of all such data in publication. In this admirable item of technic, taxonomy has been in advance of other fields of biology.
7. The classification of the species of the group to show every recognizable degree of phylogenetic affinities, the interpretation to be based on the above criteria for the recognition of relationships, upon host affinities (if available), the facts and known factors of geographic distribution, and correlation with the known geologic history of the area involved and the paleontologic history (if available) of the group and all closely related groups.
8. The interpretation of biologic phenomena within the group by an appeal to this phylogenetically established classification, to show the occasion and the order of evolutionary origin and the conditions of extension of the phenomena exhibited within the group.
9. The careful consideration and utilization of findings from other fields of scientific research at every step of the taxonomic investigation.The above program is an ideal not always obtainable even with the best of modern facilities, albeit a standard by which the merit of a piece of taxonomic work may be adjudged. It demands the intensive treatment of such small groups of species as genera or families in contrast to the wider fields of interest of the older systematists. It calls for the so-called revisional treatment of genera instead of the miscellaneous species descriptions of long repute. It demands that phylogenetic units, instead of local faunas or floras, be the basis of taxonomic consideration. It demands that the taxonomist's rôle as the diagnostician of specimens emanating from enthusiastic collectors and hard-pressed economic entomologists be subordinated to the phylogenetic interpretation of biologic phenomena.