No one has thought of raising the question of the fixity of varieties, yet it is as legitimate as that of the fixity of species; and we might also argue for the fixity of genera, orders, classes; the fixity of all these being implied in the very terms; since no sooner does any departure from the type present itself, than by that it is excluded from the category; no sooner does a white object become gray, or yellow, than it is excluded from the class of white objects. Here, therefore, is a sense in which the phrase “fixity of species” is indisputable; but in this sense the phrase has never been disputed. When zoologists have maintained that species are variable, they have meant that animal forms are variable; and these variations, gradually accumulating, result at last in such differences as are called specific. Although some zoologists, and speculators who were not zoologists, have believed that the possibility of variation is so great that one species may actually be transmuted into another, i.e., that an ass may be developed into a horse,—yet most thinkers are now agreed that such violent changes are impossible; and that every new form becomes established only through the long and gradual accumulation of minute differences in divergent directions.
It is clear, from what has just been said, that the many angry discussions respecting the fixity of species, which, since the days of Lamarck, have disturbed the amity of zoologists and speculative philosophers, would have been considerably abbreviated, had men distinctly appreciated the equivoque which rendered their arguments hazy. I am far from implying that the battle was purely a verbal one. I believe there was a real and important distinction in the doctrines of the two camps; but it seems to me that had a clear understanding of the fact that Species was an abstract term, been uniformly present to their minds, they would have sooner come to an agreement. Instead of the confusing disputes as to whether one Species could ever become another Species, the question would have been, Are animal forms changeable? Can the descendants of animals become so unlike their ancestors, in certain peculiarities of structure or instinct, as to be classed by naturalists as a different species?
No sooner is the question thus disengaged from equivoque, than its discussion becomes narrowed within well-marked limits. That animal forms are variable, is disputed by no zoologist. The only question which remains is this: To what extent are animal forms variable? The answers given have been two: one school declaring that the extent of variability is limited to those trifling characteristics which mark the different Varieties of each Species; the other school declaring that the variability is indefinite, and that all animal forms may have arisen from successive modifications of a very few types, or even of one type.
Now, I would call your attention to one point in this discussion, which ought to be remembered when antagonists are growing angry and bitter over the subject: it is, that both these opinions are necessarily hypothetical—there can be nothing like positive proof adduced on either side. The utmost that either hypothesis can claim is, that it is more consistent with general analogies, and better serves to bring our knowledge of various points into harmony. Neither of them can claim to be a truth which warrants dogmatic decision.
Of these two hypotheses, the first has the weight and majority of authoritative adherents. It declares that all the different kinds of Cats, for example, were distinct and independent creations, each species being originally what we see it to be now, and what it will continue to be as long as it exists: lions, panthers, pumas, leopards, tigers, jaguars, ocelots, and domestic cats, being so many original stocks, and not so many divergent forms of one original stock. The second hypothesis declares that all these kinds of cats represent divergencies of the original stock, precisely as the Varieties of each kind represent the divergencies of each Species. It is true that each species, when once formed, only admits of limited variations; any cause which should push the variation beyond certain limits would destroy the species,—because by species is meant the group of animals contained within those limits. Let us suppose the original stock from which all these kinds of cats have sprung, to have become modified into lions, leopards, and tigers—in other words, that the gradual accumulation of divergencies has resulted in the whole family of cats existing under these three forms. The lions will form a distinct species; this species varies, and in the course of long variation a new species, the puma, rises by the side of it. The leopards also vary, and let us suppose their variation at length assumes so marked a form,—in the ocelot,—that we class it as a new species. There is nothing in this hypothesis but what is strictly consonant with analogies; it is only extending to Species what we know to be the fact with respect to Varieties; and these Varieties which we know to have been produced from one and the same Species are often more widely separated from each other than the lion is from the puma, or the leopard from the ocelot. Mr. Darwin remarks that “at least a score of pigeons might be chosen, which, if shown to an ornithologist, and he were told that they were wild birds, would certainly, I think, be ranked by him as well-defined species. Moreover, I do not believe that any ornithologist would place the English carrier, the short-faced tumbler, the runt, the barb, the pouter and fantail in the same genus! more especially as in each of these breeds several truly-inherited sub-breeds or species, as he might have called them, could be shown him.”
The development of numerous specific forms, widely distinguished from each other, out of one common stock, is not a whit more improbable than the development of numerous distinct languages out of a common parent language, which modern philologists have proved to be indubitably the case. Indeed, there is a very remarkable analogy between philology and zoology in this respect: just as the comparative anatomist traces the existence of similar organs, and similar connections of these organs, throughout the various animals classed under one type, so does the comparative philologist detect the family likeness in the various languages scattered from China to the Basque provinces, and from Cape Comorin across the Caucasus to Lapland—a likeness which assures him that the Teutonic, Celtic, Windic, Italic, Hellenic, Iranic, and Indic languages are of common origin, and separated from the Arabian, Aramean, and Hebrew languages, which have another origin. Let us bring together a Frenchman, a Spaniard, an Italian, a Portuguese, a Wallachian, and a Rhætian, and we shall hear six very different languages spoken, the speakers severally unintelligible to each other, their languages differing so widely that one cannot be regarded as the modification of the other; yet we know most positively that all these languages are offshoots from the Latin, which was once a living language, but which is now, so to speak, a fossil. The various species of cats do not differ more than these six languages differ: and yet the resemblances point in each case to a common origin. Max Müller, in his brilliant essay on Comparative Mythology,[13] has said:—
“If we knew nothing of the existence of Latin—if all historical documents previous to the fifteenth century had been lost—if tradition, even, was silent as to the former existence of a Roman empire, a mere comparison of the six Roman dialects would enable us to say, that at some time there must have been a language from which all these modern dialects derived their origin in common; for without this supposition it would be impossible to account for the facts exhibited by these dialects. Let us look at the auxiliary verb. We find:—
| Italian. | Wallachian. | Rhætian. | Spanish. | Portuguese. | French. | |
|---|---|---|---|---|---|---|
| I am | sono | sum sunt | sunt | soy | sou | suis |
| Thou art | sei | es | eis | eres | es | es |
| He is | e | é (este) | ei | es | he | est |
| We are | siamo | súntemu | essen | somos | somos | sommes |
| You are | siete | súnteti | esses | sois | sois | êtes (estes) |
| They are | sono | súnt | eân (sun) | son | são | sont. |
It is clear, even from a short consideration of these forms, first, that all are but varieties of one common type; secondly, that it is impossible to consider any one of these six paradigms as the original from which the others had been borrowed. To this we may add, thirdly, that in none of the languages to which these verbal forms belong, do we find the elements of which they could have been composed. If we find such forms as j’ai aimé, we can explain them by a mere reference to the radical means which French has still at its command, and the same may be said even of compounds like j’aimerai, i.e. je-aimer-ai, I have to love, I shall love. But a change from je suis to tu es is inexplicable by the light of French grammar. These forms could not have grown, so to speak, on French soil, but must have been handed down as relics from a former period—must have existed in some language antecedent to any of the Roman dialects. Now, fortunately, in this case, we are not left to a mere inference, but as we possess the Latin verb, we can prove how, by phonetic corruption, and by mistaken analogies, every one of the six paradigms is but a national metamorphosis of the Latin original.
“Let us now look at another set of paradigms:—