Part 6

The term "species" was at first used very loosely by scientific writers. It meant very little more than our vague word kind does at the present time. Not until the time of Linnæus (1707-1778) did the term acquire a definite and precise meaning. The aphorism of the great botanist, "species tot sunt diversæ quot diversæ formæ ab initio sunt creatæ"--"just so many species are to be reckoned as there were forms created in the beginning,"--was at least an attempt to use the term in a well-defined sense. Of course, this definition assumed the "fixity" of species; but with the wide prevalence of the views of Darwin and his followers the term "species" has fallen into disrepute, and is now regarded by many as only an artificial rank in classification corresponding to no objective reality in the natural world. Some writers, as Lankester, have found so much fault with the term as to urge its complete abandonment in scientific literature. This is logical enough from the standpoint of Darwinism; for if the latter be true there ought indeed to be such a swamping of every incipient "species" as to make one kind blend with others all around it in the classification series.

But since the term has by no means been discarded, we must endeavor to determine the sense in which it continues to be used in good scientific literature.

"A species," says Huxley, "is the smallest group to which distinct and invariable characters can be assigned." The Standard Dictionary says that the term is used for "a classificatory group of animals or plants subordinate to a genus, and having members that differ among themselves only in minor details of proportion and color, and are capable of fertile interbreeding indefinitely."

The latter authority also adds:

"In the kingdoms of organic nature species is founded on identity of form and structure, and specifically characterized by the power of the individuals to produce beings like themselves, who are in turn productive."

To put the matter still more definitely before the reader, we quote the following from a well-known scientist whose writings on the subject of evolution have had a wide circulation:

"There are two bases on which species may be founded. Species may be based on form, morphological species; or they may be based on reproductive functions, physiological species. By the one method a certain amount of difference of form, structure, and habit, constitutes species; according to the other, if the two kinds breed freely with each other and the offspring is indefinitely fertile, the kinds are called varieties, but if they do not they are called species."

This author adds that this physiological test, as to whether or not the kinds are cross fertile, "is regarded as a most important test of true species, as contrasted with varieties or races."

III

When we look at the matter in this light, it is very evident that there are multitudes of long recognized specific distinctions that ought to be discarded. For instance, there are some twenty odd "species" of wild pigs scattered over the Old World, which Flower and Lydekker assure us would probably "breed freely together." The yak and the zebu of India, and the bison of America, would on this basis have to be surrendered, for it is well known that they will all breed freely with the common domestic cattle, as well as with one another. Perhaps all or nearly all of the dozen or more "species" of the genus Bos would thus be included together. All of the dogs, wolves, and others of the Canidæ might thus be considered as fundamentally a unit. The cats (Felidæ) are well known to breed freely together, Karl Hagënbeck of Hamburg having crossed lions and tigers as well as others of the family. Practically all of the bears have been crossed repeatedly, and the progeny of these and other crosses are quite familiar sights at the London Zoölogical Gardens. Among the lower forms of life even more surprising results have been attained by Thomas Hunt Morgan and others.

It would, however, be a very hasty conclusion to say on the basis of these facts that there are no natural limitations to groups of animals and plants. But we are entirely warranted in concluding from these facts that in very many cases, perhaps in most, our system of taxonomic classification of animals and plants has gone altogether too far, and that scientists have erected specific distinctions which are wholly uncalled for and which confuse and obscure the main issues of the species problem. Among the workers in botany and in every department of zoölogy there have always been the "splitters" and the "lumpers," as they are familiarly called; the former insisting on the most minute distinctions between their "species," thus multiplying them; the latter being more liberal and tending to diminish the number of species in any given group. For a generation or more in the recent past the "splitters" had things pretty much their own way; but of late there is a growing tendency to frown down the mania for creating new names. Even yet it is with the utmost reluctance that long established specific distinctions are surrendered, as is illustrated in the case of the mammoth, which is acknowledged by some of the very best authorities to be really indistinguishable from the modern Asiatic elephant. Several fossil bears were long listed in scientific books; but they are all acknowledged now to be identical with the modern grizzly, and as we have already intimated all the modern ones ought to be put together. These modern rationalizing methods have made but a slight impression on the vast complex of the fossil plants and animals, affecting the names of only a few of the larger and better known forms. In the realm of invertebrate palæontology, however, the "splitters" are still holding high carnival, in spite of the efforts of some very prominent scientists in the opposite direction. For palæontologists still follow the irrational course of inventing a new name, specific or even generic, for a form that happens to be found in a kind of rock widely separated as to "age" from the other beds where similar forms are accustomed to be found. As Angelo Heilprin expresses it, "It is practically certain that numerous forms of life, exhibiting no distinctive characters of their own, are constituted into distinct species for no other reason than that they occur in formations widely separated from those holding their nearest kin."

As a result of these methods this same author declares: "It is by no means improbable that many of the older genera, now recognized as distinct by reason of our imperfect knowledge concerning their true relationships, have in reality representatives living in the modern seas."

But the situation is very little better when we come to deal with plants and animals of our modern world. Because, with the many thousands of students of natural science all over the world, each anxious to get into print as the discoverer of some new form, the systematists have a dead weight of names on their hands that by a rational and enlightened revision could doubtless be reduced to but a fraction of their present disheartening array. For as the result of the extensive breeding experiments now being carried on under the study of what is called Mendelism (a term that will be explained in the next chapter), it has been found that great numbers of the "species" of the systematists or classificationists will not stand the physiological test of breeding, that is, they are found to breed freely together according to the Mendelian Law. As William Bateson remarks:

"We may even be certain that numbers of excellent species recognized by entomologists or ornithologists, for example, would, if subjected to breeding tests, be immediately proved to be analytical varieties, differing from each other merely in the presence or absence of definite factors."

The following from David Starr Jordan, the leading American authority on fishes, will serve to show how numerous have been the new names invented in recent years, all tending further to confuse and complicate the problem of what is a species:

"In our fresh-water fishes, each species on an average has been described as new from three to four times, on account of minor variations, real or supposed. In Europe, where the fishes have been studied longer and by more different men, upwards of six or eight nominal species have been described for each one that is now considered distinct."

And again:

"Thus the common Channel Catfish of our rivers has been described as a new species not less than twenty-five times, on account of differences real or imaginary, but comparatively trifling in value."

Perhaps the reader will tolerate another somewhat long quotation because of the light which it sheds on this whole problem.

"Some years ago we had a parasite of a very destructive aphid down in our books as Lysiphlebus tritici. In carrying out our investigations it became necessary to find out whether this parasite had more than a single host insect, and whether it could develop in more than one species of aphid. To this end, recently emerged males and females were allowed to pair, after which the female oviposited in several species of aphids. Both parents were then killed and preserved and all of their progeny not used in further experiments were also preserved, and thus entire broods or families were kept together. In this way females were reared out of one host species and allowed to oviposit in others, until, often after several hosts had been employed, it would be bred back into the species whence it first originated. In all cases the host was reared from the moment of birth, while with the parasite both parents and offspring were kept together.

"The result of this little fragment of work was to send two genera and fourteen species to the cemetery--you may call it Mt. Synonym Cemetery, if you choose--while the insect involved is now Aphidius testaceipes. The systematist who studies only dried corpses will soon be out of date."

Now all this is not given to intimate that there is no scientific justification for the term "species," but to make plain to my non-professional readers what every well-informed biologist already knows, namely, that at the present time the "species question" is still in a very unsatisfactory state. The facts given above would strongly suggest that there probably is indeed such a thing as a species, in the sense assigned by Linnæus, who as we have seen wished to make it a designation covering all the descendants of each distinct kind originally created. But this original aim of Linnæus is to-day not merely ignored but treated with lofty contempt; for according to the prevailing theories of evolution, all the manifold diversities of life in our modern world have come about gradually as the result of a slow development by natural process, and hence it would be vain beyond measure to attempt to determine the limits of a "species" in the sense understood by Linnæus.

But we may conclude, from the facts presented above, that if there is such a naturally delimited group as a "species" in the Linnæan sense of the word, it by no means coincides with what now passes under this name, but might include many so-called species, often a whole genus, or even several.

With this in mind, we must pass on to consider the next step in our study, as to whether new "species" are now coming into being in our modern world under scientific observation, either natural or artificial.

MENDELISM AND THE ORIGIN OF SPECIES

"Had Mendel's work come into the hands of Darwin, it is not too much to say that the history of the development of evolutionary philosophy would have been very different from that which we have witnessed."

From the latter part of the eighteenth century, attempts were continually being made to explain the origin of all organic forms by some system of development or evolution. Buffon had dwelt on the modifications directly induced by the environment. Lamarck had made much use of this idea, claiming that such modifications were transmitted to posterity, and claiming the same for the structural changes produced by use and disuse. Lamarck's work did not become at all popular while he lived, chiefly through the overpowering influence of Baron Cuvier, who had an equally fantastic scheme of his own, which may well be termed a burlesque on Creation and in which an extreme fixity of "species" was a cardinal doctrine. Erasmus Darwin and Robert Chambers in England also tried to make a theory of evolution believable; though their efforts were but little more successful in gaining the ear of the world.

But to all that had gone before Charles Darwin and A.R. Wallace (1858) added the idea of "natural selection," or "the struggle for existence," to use the respective terms coined by each of these authors, as the chief means by which the effects of variation are accumulated and perpetuated so as to build up the modern complexities of the plant and animal kingdoms. Partly because it was a psychological moment, from the fact that the uniformitarian geology of Lyell with its graded advance of existences from age to age seemed absolutely to demand some evolutionary explanation; partly because artificial selection was a familiar idea of proved value in selective breeding, and "natural selection" seemed an exact parallel carried on by nature in the direction of continual improvement; but perhaps more largely because the abstract idea of "natural selection" involved so many intricate separate concepts that for nearly a generation scarcely two naturalists in the world could state the whole problem of the theory exactly alike;--on all these accounts the theory of natural selection, or of the "survival of the fittest," to use the phrase of Herbert Spencer, became in the latter decades of the nineteenth century well-nigh universal.