Читать книгу Essay on the Theory of the Earth - Georges baron Cuvier - Страница 38

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I now proceed to the consideration of another objection, one, in fact, which has already been urged against me.

Why may not the presently existing races of land quadrupeds, it has been asked, be modifications of those ancient races which we find in a fossil state; which modifications may have been produced by local circumstances and change of climate; and carried to the extreme difference which they now present, during a long succession of ages?

This objection must appear strong to those especially who believe in the possibility of indefinite alteration of forms in organised bodies; and who think that, during a succession of ages, and by repeated changes of habitudes, all the species might be changed into one another, or might result from a single species.

Yet to these persons an answer may be given from their own system. If the species have changed by degrees, we ought to find traces of these gradual modifications. Thus, between the palæotheria and our present species, we should be able to discover some intermediate forms; and yet no such discovery has ever been made.

Why have not the bowels of the earth preserved the monuments of so strange a genealogy, if it be not because the species of former times were as constant as ours; or, at least, because the catastrophe which destroyed them, had not left them sufficient time for undergoing the variation alleged?

In order to reply to those naturalists who acknowledge that the varieties of animals are restrained within certain limits fixed by nature, it would be necessary to examine how far these limits extend. This is a very curious inquiry,—highly interesting in itself, under a variety of relations, and yet one that has been hitherto very little attended to.

Before entering upon this inquiry, it is proper to define what is meant by a species, so that the definition may serve to regulate the employment of the term. A species, therefore, may be defined, as comprehending the individuals which descend from each other, or from common parents, and those which resemble them as much as they resemble each other. Thus, we consider as varieties of a species, only the races more or less different which may have sprung from it by generation. Our observations, therefore, regarding the differences between the ancestors and descendants, afford us the only certain rule by which we can judge on this subject; all other considerations leading to hypothetical conclusions destitute of proof. Now, considering the varieties in this view, we observe that the differences which constitute it, depend upon determinate circumstances, and that their extent increases in proportion to the intensity of these circumstances.

Thus, the most superficial characters are the most variable: the colour depends much upon the light; the thickness of the fur upon the heat; the size, upon the abundance of food. But in a wild animal, even these varieties are greatly limited by the natural habits of the animal itself, which does not voluntarily remove far from the places where it finds, in the necessary degree, all that is requisite, for the support of its species, and does not even extend its haunts to any great distance, unless it also finds all these circumstances conjoined. Thus, although the wolf and the fox inhabit all the climates from the torrid to the frigid zone, we hardly find any other difference among them, in the whole of that vast space, than a little more or a little less beauty in their fur. I have compared skulls of foxes from the northern countries and from Egypt, with those of the foxes of France, and have found no difference but such as might be expected in different individuals. Such of the wild animals as are confined within narrower limits, vary still less, especially those which are carnivorous. The only difference between the hyena of Persia and that of Morocco, consists in a thicker or a thinner mane.

The wild herbivorous animals feel the influence of climate somewhat more extensively, because there is added to it in their case, the influence of the food, which may happen to differ both as to quantity and quality. Thus, the elephants of one forest are often larger than those of another; and their tusks are somewhat longer in places where their food may happen to be more favourable for the production of the matter of ivory. The same may take place with regard to the horns of rein-deer and stags. But let us compare two elephants the most dissimilar, and we shall not discover the slightest difference in the number and articulations of the bones, the structure of the teeth, &c.

Besides, the herbivorous species, in the wild state, seem more restrained from dispersing than the carnivorous animals, because the sort of food which they require, combines with the temperature to prevent them.

Nature also takes care to guard against the alteration of the species, which might result from their mixture, by the mutual aversion with which it has inspired them. It requires all the ingenuity and all the power of man to accomplish these unions, even between species that have the nearest resemblances. And, when the individuals produced by these forced conjunctions are fruitful, which is very seldom the case, their fecundity does not continue beyond a few generations; and would not probably proceed so far, without a continuance of the same cares which excited it at first. Thus, we never see in our woods individuals intermediate between the hare and the rabbit; between the stag and the doe; or between the martin and the pole-cat.

But the power of man changes this order; it discloses all those variations, of which the type of each species is susceptible; and from them derives productions which the species, if left to themselves, would never have yielded.

Here the degree of the variations is still proportional to the intensity of their cause, which is slavery. It is not very high in the semi-domesticated species, such as the cat. A softer fur; more brilliant colours; greater or less size; these form the whole extent of the variations in this species; for the skeleton of an Angora cat differs in no regular and constant circumstance from that of a wild cat.

In the domesticated herbivorous animals, which we transport into all kinds of climates, and subject to all kinds of management, both with regard to labour and nourishment, we certainly obtain greater variations; but still they are all merely superficial. Greater or less size; longer or shorter horns, or even the want of these entirely; a hump of fat, larger or smaller, on the shoulder; these form the differences between the various races of the common ox or bull; and these differences continue long, even in such breeds as have been transported from the countries in which they were produced, when proper care is taken to prevent crossing.

Of this nature are also the innumerable varieties of the common sheep, which consist chiefly in differences of their fleeces, as the wool which they produce is an important object of attention. These varieties, although not quite so perceptible, are yet sufficiently marked among horses. In general, the forms of the bones vary little; their connections and articulations, and the forms of the large grinding teeth, never vary at all.

The small size of the tusks in the domestic hog, compared with the wild boar’s, and the junction of its cloven hoofs into one in some races, form the extreme point of the differences which we have produced in the domesticated herbivorous quadrupeds.

The most remarkable effects of the influence of man are manifested in the animal which he has reduced most completely under subjection, the dog,—that species so entirely devoted to ours, that even the individuals of it seem to have sacrificed to us their will, their interest, and inclination. Transported by man into every part of the world, subjected to all the causes capable of influencing their development, regulated in their sexual intercourse by the pleasure of their masters, dogs vary in colour; in the quantity of their hair, which they sometimes even lose altogether, and in its nature; in size, which varies as one to five in the linear dimensions, amounting to more than a hundred fold in bulk; in the form of the ears, nose, and tail; in the proportional length of the legs; in the progressive development of the brain in the domestic varieties, whence results the form of their head, which is sometimes slender, with a lengthened muzzle and flat forehead, and sometimes having a short muzzle and a protuberant forehead; insomuch that the apparent differences between a mastiff and a water-spaniel, and between a greyhound and a pug, are more striking than those that exist between any two species of the same natural genus in a wild state. Finally, and this may be considered as the maximum of variation hitherto known in the animal kingdom, there are races of dogs which have an additional toe on the hind foot, with corresponding tarsal bones; as there are, in the human species, some families that have six fingers on each hand. Yet, in all these varieties, the relations of the bones remain the same, nor does the form of the teeth ever change in any perceptible degree; the only variation in respect to these latter being, that, in some individuals, one additional false grinder appears, sometimes on the one side, and sometimes on the other[82].

Animals, therefore, have natural characters, which resist every kind of influence, whether natural or produced by human interference, and nothing indicates that, with regard to them, time has more effect than climate and domestication.

I am aware that some naturalists lay great stress upon the thousands of ages which they call into action by a dash of the pen; but, in such matters, we can only judge of what a long period of time might produce, by multiplying in idea what a less time produces. With this view, I have endeavoured to collect the most ancient documents relating to the forms of animals; and there are none which equal, either in antiquity or abundance, those that Egypt furnishes. It affords us, not only representations of animals, but even their identical bodies embalmed in its catacombs.

I have examined with the greatest attention the figures of quadrupeds and birds sculptured upon the numerous obelisks brought from Egypt to ancient Rome. All these figures possess, in their general character, which alone could be the object of attention to an artist, a perfect resemblance to the species represented, such as we see them at the present day.

On examining the copies made by Kirker and Zoega, we find that, without preserving every trait of the originals in its perfect purity, they have given figures which are easily recognised. We readily distinguish the ibis, the vulture, the owl, the falcon, the Egyptian goose, the lapwing, the landrail, the aspic, the cerastes, the Egyptian hare with its long ears, and even the hippopotamus; and, among the numerous monuments engraved in the great work on Egypt, we sometimes observe the rarest animals, the algazel, for example, which was not seen in Europe until within these few years[83].

My learned colleague, M. Geoffroy Saint-Hilaire, strongly convinced of the importance of this research, carefully collected in the tombs and temples of Upper and Lower Egypt as many mummies of animals as he could. He has brought home cats, ibises, birds of prey, dogs, monkeys, crocodiles, and the head of an ox, in this state; and there is certainly no more difference to be perceived between these mummies and the species of the same kind now alive, than between the human mummies and the skeletons of men of the present day. A difference may, indeed, be found between the mummies of the ibis and the bird which naturalists have hitherto described under that name; but I have cleared up all doubts on this matter, in a Memoir upon the Ibis, which will be found at the end of this Essay, and in which I have shewn that it is still at the present day the same as it was in the time of the Pharaohs. I am aware that, in these, I only cite the monuments of two or three thousand years; but this is the most remote antiquity to which we can resort in such a case.

There is nothing, therefore, to be derived from all the facts hitherto known, that could, in the slightest degree, give support to the opinion that the new genera which I have discovered or established among the fossil remains of animals, any more than those which have in like manner been discovered or established by other naturalists, the palæotheria, anoplotheria, megalonyces, mastodonta, pterodactyli, ichthyosauri, &c. might have been the sources of the present race of animals, which have only differed from them through the influence of time or climate. Even if it should prove true, which I am far from believing to be the case, that the fossil elephants, rhinoceroses, elks, and bears, differ no more from those at present existing, than the present races of dogs differ from one another, this would not furnish a sufficient reason for inferring the general identity of the species, because the races of dogs have been subjected to the influence of domestication, which these other animals neither did nor could experience.

Farther, when I maintain that the rocky beds contain the bones of several genera, and the alluvial strata those of several species which no longer exist, I do not assert that a new creation was required for producing the species existing at the present day. I only say that they did not originally inhabit the places where we find them at present, and that they must have come from some other part of the globe.

Let us suppose, for instance, that a great irruption of the sea were now to cover the continent of New Holland with a coat of sand or other debris; it would bury the carcases of animals belonging to the genera Kangurus, Phascolomys, Dasyurus, Perameles, flying phalanger, echidna, and ornithorynchus, and it would entirely destroy the species of all these genera, since none of them exist now in any other country.

Were the same revolution to lay dry the numerous narrow straits which separate New Holland from the continent of Asia, it would open a road to the elephants, rhinoceroses, buffaloes, horses, camels, and tigers, and to all the other Asiatic quadrupeds, which would come to people a land where they had been previously unknown.

Were some future naturalist, after having made himself well acquainted with this new race of animals, to search below the surface on which they live, he would find remains of quite a different nature.

What New Holland would be, under the circumstances which we have supposed, Europe, Siberia, and a large portion of America, now actually are. And, perhaps, when other countries shall have been examined, and New Holland among the rest, it will one day be found that they have experienced similar revolutions, I might almost say, mutual changes, of productions. For, if we push the supposition farther, and, after the supply of Asiatic animals to New Holland, admit a second revolution, which destroyed Asia, their original country, those naturalists who might observe them in New Holland, their second country, would be equally at a loss to know whence they had come, as we now are to find out the origin of the races of animals that inhabit our own countries.

I now proceed to apply this manner of reasoning to the human species.