In nature one encounters all sorts of different animals intermingling without any apparent law or order. It is necessary, therefore, with all this diversity to invent some workable system that will bring cosmos out of chaos and make “type study” possible, otherwise confusion is inevitable and the effort to become familiar with all living things is hopeless.
First of all it is essential to become acquainted with as many kinds of animals as possible, not alone through pictures and names of animals that live so dreary a life in textbooks, but through actual acquaintance with real animals. Taxonomy, or classification of animals and plants, is dull and without point until one has gained a personal acquaintance with enough organisms to make it worth while. This chapter consequently should be referred to only as a last resort after various kinds of animals encountered begin to be familiar and interesting, and there is something to classify.
Classifications, it should be noted, are more than arbitrary sets of pigeon-holes labeled with forbidding technical names, in which to file away and forget our animal associates, for they involve a compact summary of knowledge concerning the origin and derivation of different organisms.
In mentally putting together animals of a kind, the ideal criterion to employ is hereditary relationship rather than external resemblance. It is the particular province of comparative morphology to discover such relationships. A whale, for example, is properly classified with mammals rather than with fishes, which it superficially resembles and with which it associates, because its common origin with animals of the mammalian type is indicated by the fundamental fact that, along with many other mammalian peculiarities, its young are born alive and fed at first upon milk.
Superficial features, like the transparency of many open-sea forms as diverse as jellyfish, shrimp, pteropod mollusks, worms, and larval fishes, or the power of aerial flight on the part of such plainly unrelated creatures as birds, bees, and bats, tell us where the animal has been spending its life, while animals as unlike in appearance as whales and bats, herons and hummingbirds, eels and flatfishes, butterflies and bedbugs, or lobsters and barnacles, belong together in any scientific classification, because each pair is built on the same fundamental plan and has a blood relationship, one with the other.
Owing to the incompleteness of our present knowledge about the evolution and blood relationship of animals there is still considerable uncertainty and controversy among taxonomists as to “who’s who” in any classification, and as a result several different arrangements are current in books dealing with the subject. The same scientist, as his store of knowledge grows, may change his original classification. For instance, David Starr Jordan, America’s foremost authority on the group of fishes, in a classification of North American fishes (Jordan and Copeland) in 1876, named 670 species. Twenty-two years later, in 1898, he published a new list (Jordan and Everman) including in it only 585 species in spite of the fact that meanwhile 130 new species had been brought to light.
Ward refers to two kinds of taxonomists, namely, “hair-splitters” and “lumpers,” and we are free to choose between them, for there is no indisputable hard and fast classification that we are bound to accept to the exclusion of all others.
Although opinions differ with regard to the details of systems of classification, there is substantial agreement with regard to the sequence of the following groups in which
The manner of employing these groups may be illustrated by classifying a particular individual house cat, named “Tom” (Fig. 7). It will be seen that this cat finds itself admitted successively into more and more inclusive groups, until finally, as a member of the vast animal kingdom, it has quite lost its individual importance. If now we retrace our steps in the diagram from the all-inclusive animal kingdom, we see the individuality of “Tom” gradually emerging until it may be concluded that this cat at least possesses not only the general characteristics listed in the preceding chapter as vertebrate characteristics, but also that it has the special equipment that makes it a mammal and a carnivore, like the lions, tigers, and their kind, and last of all it has an individuality that distinguishes it from all other domestic cats which are well known in their several households.
Although Darwin, who wrote The Origin of Species, was unable to define just what are the limits of a species, which is a concept that has no exact counterpart in nature, he nevertheless made it clear that a species is a real entity that outlives the separate individuals composing it. The species concept of “cats” will remain long after the individual Tom has lived out the traditional nine lives of cats and turned to dust.