Taxonomic classification

“ The contrasting patterns in the description of new species and new higher taxa suggest that taxonomic effort is probably not driving observed flattening of accumulation curves in higher taxonomic levels as there is at least sufficient effort to maintain a constant description of new species. ”

“ From a further consideration of the foregoing principles it will be seen that all existing species are held to be descended by true generation from pre-existing species, and that, consequently, all the relationships we observe between species are explained by community of origin. The most natural system of classification is, therefore, that which best reveals the scheme of descent, or, as it is termed, the phylogeny, of the group of organisms classified. ”

“ In order to identify a species, the genus to which it belongs must be stated, hence the term, binomial system of nomenclature, which Linnæus introduced, becoming trinomial when the name of a subspecies is added, a modern refinement on the older method. A very large species (i.e. one which is represented by great numbers of individuals) , extending over a very large area, is often divisible into groups of minor rank, as varieties, geographical races or subspecies. Taking the species as the unit in the scheme of classification, the varieties and subspecies may be considered as fractions. ”

“ 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. ”

“ They argued taxonomy needed rules around what should be called a species, because currently there are none. They wrote:
for a discipline aiming to impose order on the natural world, taxonomy (the classification of complex organisms) is remarkably anarchic [...] There is reasonable agreement among taxonomists that a species should represent a distinct evolutionary lineage. But there is none about how a lineage should be defined. ‘Species’ are often created or dismissed arbitrarily, according to the individual taxonomist's adherence to one of at least 30 definitions. ”

“ We here regard species alone as entitled to distinct botanical appelation; it has been suggested that races may be indicated numerically.
Other than the omission of descriptions of varieties, the general system of classification used in the first edition has been maintained in the second. A few new family groups and a number of genera have been separated or distinguished from their congeners. ”

“ The same difficulty may occur in defining a genus, on account of the extent to which some of its species differ from others, whilst having enough of the common character to deter the classifier from forming a distinct genus on their account. On the other hand the occurrence of numerous intermediate varieties may make it difficult to distinguish genera or species at all. Even the Kingdoms of plants and animals are hard to discriminate at the lowest levels of organisation. Now, where there is a difficulty of classification there must be a corresponding difficulty of definition. ”

“ Variety comes in upon occasion. For, although a species may have no recognized varieties, a genus implies at least one species belonging to it; every genus is of some order, and every order of some class.
533. But these grades by no means exhaust the resources of classification, nor suffice for the elucidation of all the distinctions which botanists recognize. In the first place, a higher grade than that of class is needful for the most comprehensive of divisions, that of all plants into the two Series of Phanerogamous and Cryptogamous (6) ”

“ Domestic varieties can be classed in groups under groups, like species under genera, and these under families and orders; and the classification may be either artificial,—that is, founded on any arbitrary character,—or natural. With varieties a natural classification is certainly founded, and with species is apparently founded, on community of descent, together with the amount of modification which the forms have undergone. ”

“ Every zoologist and botanist is aware that it is a comparatively easy task to establish genera in departments which have been enriched [p.107] with only a small number of species, and where there is as yet no tendency in one set of characters to pass almost insensibly, by a multitude of connecting links, into another. They also know that the difficulty of classification augments, and that the artificial nature of their divisions becomes more apparent, in proportion to the increased number of objects brought to light. ”

“ First, As to the alleged absence of intermediate varieties connecting one species with another, every zoologist and botanist who has engaged in the task of classification has been occasionally thrown into this dilemma,—if I make more than one species in this group, I must, to be consistent, make a great many. ”

“ The system of binomial nomenclature has led to the development of the science of taxonomy, the systematic classification and naming of plants and animals according to their relationships.
THE UNITS OF CLASSIFICATION
The world of organic life has been divided into the plant and animal kingdoms. These kingdoms have been further divided into larger divisions called phyla (from the Greek word phylon, a race) . Each phylum is composed of organisms with certain characteristics in common. For example, all animals with a spinal cord (or notochord) are assigned to the phylum Chordata. ”

“ In fact, it is anticipated that transparent governance of a unified global list will enhance the scientific reputation of taxonomy by showcasing the strengths and merits of both the decision-making process and the underlying taxonomic research on which the list is based.
6. The set of criteria considered sufficient to recognise species boundaries may appropriately vary between different taxonomic groups but should be consistent when possible
There is no universally accepted definition of a species. ”

“ Linnaeus' invention of binomial nomenclature for designating species served systematic biology admirably, but at the same time, by attaching preponderating importance to a particular grade in classification, crystallized the doctrine of fixity. The lower grades in classification such as sub-species and varieties on the one hand, and the higher grades on the other, such as genera and families, were admitted to be human conceptions imposed on the living world, but species were concrete, objective existences to be discovered and named. ”

“ It is equally impossible at present to distinguish different types of endemics, such as relictae, etc., as any such classification must await the elaboration of a method for determining the phylogeny of a natural group of species by an investigation of their comparative differentiation in connection with their migration in all directions from the vegetation center into new habitats. In short, it will not be possible to make a thorough study of endemism and to postulate its laws until modern methods of research have been extended to a much larger portion of the vegetation of the globe. ”

“ To what extent these hints for the discrimination of species will be found to avail in practice, it is difficult to say, but it seems desirable that they should speedily be brought to the test of experience, since there is no genus, of the same extent, in which it is so difficult to determine the species. ”

“ While interpretation will always play a part in taxonomy, the general use of experiment will leave much less opportunity for the personal equation than is at present the case. Taxonomy, like descriptive botany, is based upon the species, but, while there may exist a passable kind of descriptive botany, there can be no real taxonomy as long as the sole criterion of a species is the difference which any observer thinks he sees between one plant and another. The so-called species of to-day range in value from mere variations to true species which are groups of great constancy and definiteness. ”

“ In a finely divided classification, printing of titles for all genera is not practicable; hence great care ought to be directed toward grouping species according to the principles of arrangement herein outlined, noting that whenever a change of basis is made, a new genus is implied, and that subclasses for all other species of the same genus under whatever name, must be brought into juxtaposition as if indented under the implied genus. ”

“ As a rule, however, formations most frequently show endemic habitat forms and species, more rarely endemic genera; regions and provinces commonly exhibit endemic species and genera, rarely endemic families; while zones and hemispheres contain endemic orders as well as families. This correspondence is readily seen to depend primarily upon the fact that increased differentiation in the taxonomic sense is a concomitant of the increased invasion of endemic species, measured in terms of distance and difference in habitat. ”

“ A perfect taxonomy is one which would perfectly express all the facts in the evolution and development of the various forms. It would be based on morphology, the consideration of structure and form independent of adaptive, or physiological, or environmental modifications. It would regard those characters as most important which had existed longest unchanged in the history of the species or type, thus considering all knowledge derived from paleontology. ”

“ Third, it forces other users, who may lack relevant taxonomic expertise, to choose between competing lists and taxonomic treatments of groups even though they rarely understand the rationale why competing lists exist and are confused by the differences between alternate taxonomic concepts and classifications. ”

“ The suggestion of applying qualifying terms to each and all of the varieties of a subspecifically divided species is most wholesome, and should be applied to the scientific as well as the vernacular nomenclatural system. Modern subspecific ideas should not recognize the superiority of one variety over another without good evolutionary reasons for so doing. Why call one form a species and the rest varieties just because one of them had, of necessity, to be discovered first? ”

“ An important caveat to the interpretation of our results concerns the definition of species. Different taxonomic communities (e.g., zoologists, botanists, and bacteriologists) use different levels of differentiation to define a species. This implies that the numbers of species for taxa classified according to different conventions are not directly comparable. For example, that prokaryotes add only 0.1% to the total number of known species is not so much a statement about the diversity of prokaryotes as it is a statement about what a species means in this group. ”

“ Vertical lines indicate the consensus standard error. (P–T) Frequency distribution of the number of subordinate taxa at different taxonomic levels. For display purposes we present only the data for Animalia; lines and test statistics are from a regression model fitted with a power function. Changes in taxonomic effort
Taxonomic effort can be a strong determinant of species discovery rates [14] . Hence the estimated asymptotes from the temporal accumulation curves of higher taxa (dotted horizontal line in Figure 1A–1E) might be driven by a decline in taxonomic effort. ”

“ III. The only natural classification of the vast aggregate of diversified forms which this group contains, will be one which ranges them according to their mode and degree of divergence from a small number of principal family types; and any subordinate groupings of genera and species which may be adopted for the convenience of description and nomenclature, must be regarded merely as assemblages characterized by the nature and degree of the modifications of the original type which they may have respectively acquired in the course of genetic descent from a common ancestry. ”

“ A closer scrutiny of the facts, however, makes the term hybridism less isolated and more vague. The words species and genus, and still more subspecies and variety, do not correspond with clearly marked and sharply defined zoological categories, and no exact line can be drawn between the various kinds of crossings from those between individuals apparently identical to those belonging to genera universally recognized as distinct. ”

“ To make the denotation of zoological names precise, exact workers are endeavouring to associate the conception of types with names, a process which can be made simple and definite with new work, but which presents great difficulties in the attempt to apply it to existing terms. Every family should have designated one of its genera as the type genus, every genus a type species and so forth. In the case of species or sub-species the type is a single specimen, either the only one before the author when writing his description, or one definitely selected by him, the others being paratypes. ”

“ 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. ”