Search for "Natural" Scheme.— Facts of biology accumulated, but a connected system for "natural" classification of them eluded all searchers. That this should be the case is not surprising when one recalls that it was be lieved by all the older zoologists, except a few advanced thinkers, whose views were usually scouted, that the individuals of each kind of animal were descended from their own peculiar ancestor; that this original pair was totally unconnected with the ancestor of any other line, having, as Buffon asserted, °participated in the grace of a distinct creation)); that a species so created was forever unchangeable.
Classifiers sought to perfect their apprecia tion of resemblances, and constantly used the word relationship, but this term, when em ployed with reference to two kinds of animals having a wholly independent origin, was of course used in a purely metaphorical sense. It was not until the prevalent idea outlined above was discarded that relationship took on its real significance and became the key-word in class ification; and this came about only when the doctrine and facts of organic evolution — that is, transmutation of forms of life through vari ation in descent — destroyed the earlier concep tion of the origin and history of living things on the globe. Then it was that all the avenues of inquiry (anatomy, embryology, geographical and geological distribution, adaptations to habits, etc.) led to the same point, indicated the true place in nature of each animal or group — true because it had become so by de velopmental heredity. Instead of four or six or some other number of parallel °plans) of immutable structure, it became plain that ani mal life and plant life represented only one progressive, enlarging and ever-varying scheme of adaptative and fruitful beings.
This compelled the discarding of another old assumption, one on which, in fact, all previous schemes of classification had rested, namely, the existence and fixity of °species.° This word came into use in zoology and botany at the beginning of the 18th century, when John Ray applied it to indicate a group of animals and plants with common characteristics that would interbreed freely. (This last test has been popularly considered definite, although not universally true.) says Prof. William B. Scott in his of Land (1913), °regarded species as objective realities, con crete and actual things, which it was the nat uralist's business to discover and name, and held that they were fixed entities which had been separately created. This belief in the
fixity and objective reality of species was al most universally held until the publication of Darwin's (Origin of Species) (1859) converted the biological world to the evolutionary faith, which declares that the only objective reality among living things is the individual animal or plant.° Descent the Test of This conception upset completely all previous methods of determining relationship —the basis now, as always, of classification; and gave to that word a new and proper definition, namely, association by blood-connection de rived through descent from the same stock.
The term had been so used with refer ence to human affinities, and this meaning was now extended to all living things, as was right and natural. A man's relatives are those who belong to the same family-stock; the relation ship between them is one of blood and inherit ance. The same is true of horses, or sparrows, or fishes, or snails. Any recognizable relation ships are those produced by common descent; and when these are unrecognizable the search for them must be along lines of ancestry.
Hence the vast service of palmontology has ren dered to classification of living things —the same kind of service for the brute world that the study of genealogy has rendered to human history. Pabeontology reveals the genealogy of the animal world so far as its materials permit.
Genealogy, then, is the guide to the classifi cation of the individual, whether human, quad ruped, bird or lowly worm; and the old-fash ioned °plans of structure" are merely helpful indications of probable community of descent. They exhibit the groups that have resulted from the more or less gradual variations, pre historic divergencies, and frequent extinc tions of intermediate lines, that have affected the descent of animal life from some original source. Biological classification is the expres sion of heredity.
The matter is commonly symbolized by a tree growing from seed and root to trunk, splitting into limbs that spread out in various directions, putting forth lesser divergent branches and finally innumerable twigs. Many branches flourish to the very tip; others remain short; others produce twigs; others die and disappear. Species are the latest twigs ; the lesser branches from which they spring may represent genera, families, orders, and classes, until at last the root-trunk is reached. The figure is incomplete and inadequate, but is helpful.