Mythical Monsters. Gould Charles

date, have originated the myths, current among the Indians of South America, of a gigantic tunnelling or burrowing creature, incapable of supporting the light of day.37

       CHAPTER II.

      EXTINCTION OF SPECIES

      In reviewing the past succession of different forms of ancient life upon the globe, we are reminded of a series of dissolving views, in which each species evolves itself by an imperceptible gradation from some pre-existing one, arrives at its maximum of individuality, and then slowly fades away, while another type, either higher or lower, evolved in turn from it, emerges from obscurity, and succeeds it on the field of view.

      Specific individuality has in all cases a natural term, dependent on physical causes, but that term is in many cases abruptly anticipated by a combination of unfavourable conditions.

      Alteration of climate, isolation by geological changes, such as the submergence of continents and islands, and the competition of other species, are among the causes which have at all times operated towards its destruction; while, since the evolution of man, his agency, so far as we can judge by what we know of his later history, has been especially active in the same direction.

      The limited distribution of many species, even when not enforced by insular conditions, is remarkable, and, of course, highly favourable to their destruction. A multiplicity of examples are familiar to naturalists, and possibly not a few may have attracted the attention of the ordinary observer.

      For instance, it is probably generally known, that in our own island, the red grouse (which, by the way, is a species peculiar to Great Britain) is confined to certain moorlands, the ruffs and reeves to fen districts, and the nightingale,38 chough, and other species to a few counties; while Ireland is devoid of almost all the species of reptiles common to Great Britain. In the former cases, the need of or predilection for certain foods probably determines the favourite locality, and there are few countries which would not furnish similar examples. In the latter, the explanation depends on biological conditions dating prior to the separation of Ireland from the main continent. Among birds, it might fairly be presumed that the power of flight would produce unlimited territorial expansion, but in many instances the reverse is found to be the case: a remarkable example being afforded by the island of Tasmania, a portion of which is called the unsettled waste lands, or Western Country. This district, which comprises about one-third of the island upon the western side, and is mainly composed of mountain chains of granites, quartzite, and mica schists, is entirely devoid of the numerous species of garrulous and gay-plumaged birds, such as the Mynah mocking-bird, white cockatoo, wattle bird, and Rosella parrot, though these abundantly enliven the eastern districts, which are fertilized by rich soils due to the presence of ranges of basalt, greenstone, and other trappean rocks.

      Another equally striking instance is given by my late father, Mr. J. Gould, in his work on the humming-birds. Of two species, inhabiting respectively the adjacent mountains of Pichincha and Chimborazo at certain elevations, each is strictly confined to its own mountain; and, if my memory serves me correctly, he mentions similar instances of species peculiar to different peaks of the Andes.

      Limitation by insular isolation is intelligible, especially in the case of mammals and reptiles, and of birds possessing but small power of flight; and we are, therefore, not surprised to find Mr. Gosse indicating, among other examples, that even the smallest of the Antilles has each a fauna of its own, while the humming-birds, some of the parrots, cuckoos, and pigeons, and many of the smaller birds are peculiar to Jamaica. He states still further, that in the latter instance many of the animals are not distributed over the whole island, but confined to a single small district.

      Continental limitation is effected by mountain barriers. Thus, according to Mr. Wallace, almost all the mammalia, birds, and insects on one side of the Andes and Rocky Mountains are distinct in species from those on the other; while a similar difference, but smaller in degree, exists with reference to regions adjacent to the Alps and Pyrenees.

      Climate, broad rivers, seas, oceans, forests, and even large desert wastes, like the Sahara or the great desert of Gobi, also act more or less effectively as girdles which confine species within certain limits.

      Dependence on each other or on supplies of appropriate food also form minor yet practical factors in the sum of limitation; and a curious example of the first is given by Dr. Van Lennep with reference to the small migratory birds that are unable to perform the flight of three hundred and fifty miles across the Mediterranean. He states that these are carried across on the backs of cranes.39

      In the autumn many flocks of cranes may be seen coming from the North, with the first cold blast from that quarter, flying low, and uttering a peculiar cry, as if of alarm, as they circle over the cultivated plains. Little birds of every species may be seen flying up to them, while the twittering cries of those already comfortably settled upon their backs may be distinctly heard. On their return in the spring they fly high, apparently considering that their little passengers can easily find their way down to the earth.

      The question of food-supply is involved in the more extended subject of geological structure, as controlling the flora and the insect life dependent on it. As an example we may cite the disappearance of the capercailzie from Denmark with the decay of the pine forests abundant during late Tertiary periods.

      Collision, direct or indirect, with inimical species often has a fatal ending. Thus the dodo was exterminated by the swine which the early visitors introduced to the Mauritius and permitted to run wild there; while the indigenous insects, mollusca, and perhaps some of the birds of St. Helena, disappeared as soon as the introduction of goats caused the destruction of the whole flora of forest trees.

      The Tsetse fly extirpates all horses, dogs, and cattle, from certain districts of South Africa, and a representative species in Paraguay is equally fatal to new-born cattle and horses.

      Mr. Darwin40 shows that the struggle is more severe between species of the same genus, when they come into competition with each other, than between species of distinct genera. Thus one species of swallow has recently expelled another from part of the United States; and the missel-thrush has driven the song-thrush from part of Scotland. In Australia the imported hive-bee is rapidly exterminating the small stingless native bee, and similar cases might be found in any number.

      Mr. Wallace, in quoting Mr. Darwin as to these facts, points the conclusion that “any slight change, therefore, of physical geography or of climate, which allows allied species hitherto inhabiting distinct areas to come into contact, will often lead to the extermination of one of them.”

      It is the province of the palæontologist to enumerate the many remarkable forms which have passed away since man’s first appearance upon the globe, and to trace their fluctuations over both hemispheres as determined by the advance and retreat of glacial conditions, and by the protean forms assumed by past and existing continents under oscillations of elevation and depression. Many interesting points, such as the dates of the successive separation of Ireland and Great Britain from the main continent, can be determined with accuracy from the record furnished by the fossil remains of animals of those times; and many interesting associations of animals with man at various dates, in our present island home and in other countries, have been traced by the discovery of their remains in connection with his, in bone deposits in caverns and elsewhere.

      Conversely, most valuable deductions are drawn by the zoologist from the review which he is enabled to take, through the connected labours of his colleagues in all departments, of the distinct life regions now mapped out upon the face of the globe. These, after the application of the necessary corrections for various disturbing or controlling influences referred to above, afford proof reaching far back into past periods, of successive alterations in the disposition of continents and oceans, and of connections long since obliterated between distant lands.

      The palæontologist reasons from the past to the present, the zoologist from the present to the past; and their mutual labours explain the evolution of existing forms, and the causes of the disparity or connection between those at present characterizing the different

37

A similar habit is ascribed by the Chinese to the mammoth and to the gigantic Sivatherium (Fig. 6, p. 39), a four-horned stag, which had the bulk of an elephant, and exceeded it in height. It was remarkable for being in some respects between the stags and the pachyderms. The Dinotherium (Fig. 8), which had a trunk like an elephant, and two inverted tusks, presented in its skull a mixture of the characteristics of the elephant, hippopotamus, tapir, and dugong. Its remains occur in the Miocene of Europe.

Fig. 8. – Dinotherium. (After Figuier.)

38

“It enters Europe early in April, spreads over France, Britain, Denmark, and the south of Sweden, which it reaches by the beginning of May. It does not enter Brittany, the Channel Islands, or the western part of England, never visiting Wales, except the extreme south of Glamorganshire, and rarely extending farther north than Yorkshire.” – A. R. Wallace, Geographical Distribution of Animals, vol. i. p. 21. London, 1876.

39

Bible Customs in Bible Lands. By H. J. Van Lennep, D.D. 1875. Quoted in Nature, March 24, 1881.

40

Origin of Species, C. Darwin, 5th edit. 1869.