"For forms are variable, and decay By course of kinde, and by occasion."-SPENSER. to prevent the redundancy of species; and equally prevents their total extinction, which, on account of the unlimited powers of destruction which man possesses, would sometimes occur, were his choice more restricted. From a love of vegetable food, man is led to cultivate and render the productions of the soil abundant and wholesome; and, in like manner to the operation of his appetite upon animal productions, he is impelled, by his love of variety, to cultivate every kind of herb, shrub, and tree. 599. The instinct of hunting-if such a term may be applied to a being gifted with the superior faculty of reason-is universally diffused among men. We find the most untutored savage expert after his degree in the pursuits of the chase; and, under a régime of the most complete civilization, the gentleman is still a hunter. Fortunately for him, he follows the chase no longer from necessity, or to procure food, but simply to obtain from its mimic warfare a certain amount of relaxation and excitement. The cultivation of the soil is a gauge of civilization. Where agriculture and its kindred arts flourish, peace, health, and wealth are its attendants upon man, while the fiercer and more ferocious animals either cease to exist, or are kept within strong and impassable bounds. 600. By what means is man enabled to influence the forms and qualities of various animals which belong to them at their birth; and to create, as it were, new varieties at will? Because all the individuals of the same species do not possess, to the same degree, the physical and instinctive qualities with which the species are generally endowed; and by the exercise or the influence of physical conditions, man can develop a particular faculty, and consequently increase these differences. He may, within certain limits, modify races at his pleasure; for he is able to choose, or even to produce, individual differences, which are transmissable from one to the other; and to regulate the succession of generations, so as to remove from them all that would tend to separate the race from the type which he wishes to produce; and he can thus influence the hereditary qualities of the young, as he had done those of their parents. "As Jacob used an ingenious invention to make Laban's cattle speckled or ring-staked, so much the skill in making tulips feathered and variegated, with stripes of divers colours," FULLER. 601. This is especially the case with our various domesticated animals; and there are none that show it more strongly than dogs. Not only do the different races of dogs vary in the colour and quantity of their hair, but also in the proportions of the different parts of their bodies, and even in their instincts. How different, for example, are the greyhound and the mastiff, the bloodhound and the spaniel. We could scarcely imagine that any period of time, or external influence, could ever convert one into the other. And yet they had one common origin; and it is found that their distinct forms are preserved only so long as they are matched in breeds. Among the problems of high theoretical interest which the recent progress of geology and natural history has brought into notice, no one is more prominent, and, at the same time, more obscure, than that relating to the origin of species. On this difficult and mysterious subject Mr. Charles Darwin has bestowed long and anxious attention; and the result of some twenty years' observation and experiments in zoology, botany, and geology, has established in his mind the conclusion that those powers of nature which give rise to races and permanent varieties in animals and plants, are the same as those which, in much longer periods, produce species, and in a still longer series of ages, give rise to differences of generic rank.* 602. How is the distribution of animals over the surface of the globe accounted for? Several hypotheses have been set up to account for this *Professor Lyell. "The heavenly bodies (as growne now lesse strong) All climats still new temperatures embrace, What strange effects must follow them ere long?"-STIRLING. distribution. But it may not be unreasonable to assume that at the beginning of the actual geological period, the various species were limited to narrow regions, and that by degrees they afterwards spread to a distance, so as to occupy a more or less considerable portion of the surface of the globe. 603. The circumstances which favour the dissemination of species are of two kinds. The first is connected with or dependent on the nature of the animal; the second, with causes foreign to it. In the number of the first, the development of the locomotive power holds an important place. All things being equal, the species which live fixed to the soil, or which possess but imperfect instruments for locomotion, occupy but a restricted portion of the surface of the globe, compared with the species whose movements of translation are rapid and energetic. Thus, birds have a most extended area, whilst reptiles, on the contrary, are generally confined to narrow limits. 604. Why do differences of climate serve to arrest the march of animals from one region to another? Because there are throughout all nature, mutual adaptations of animate and inanimate existences—of organic and inorganic forms. This is seen in the growth of vegetables, as well as in the development of animals. 605. Apes, which crowd the tropical regions, almost always die of pulmonary consumption when they are exposed to the coldness and humidity of our climate; while the rein-deer, formed to support the rigours of a long and rude Lapland winter, suffers from heat at St. Petersburg, and in general sinks quickly under the influence of a temperate climate. Man and the dog are the only species that can support the two extremes of arctic cold and tropical heat. The influence of temperature on the animal economy explains to us why certain species remain cantoned in a chain of mountains, without being able to spread abroad into analogous localities. We know that the temperature decreases by reason of the elevation of the soil; and that, in consequence, animals which live at considerable elevations could not descend into the low plains to reach other mountains without traversing countries where the temperature is much superior to that of their ordinary habitation. "What means the bull, unconscious of his strength, to play the coward, and flee before such a feeble thing as man?"-BLAIR 606. Why are the largest quadrupeds found in Africa and the largest reptiles in America? Africa abounds in dry deserts, and is the most luxurious as to its vegetable productions, which circumstances are favourable to the growth of such animals as elephants, rhinoceri, and hippopotami. The vast swamps which border the great American rivers naturally favour the development of the reptile order, and there abound the largest species and the greatest variety. 607. What relation exists between the elevation of temperature in different zoological regions, and the organic perfection of the animals inhabiting them? In the hottest climates the animals are found most to approach man; and those which in each great zoological division possess the organization the most complex, and the faculties most developed; whilst in the polar regions we meet only with beings occupying a rank but little elevated in the zoological series. The apes, for example, are limited to the hottest parts of the two continents; it is the same with parrots among birds; the crocodile and tortoise amongst reptiles; and of land-crabs amongst the crustacea―all animals the most perfect in their respective classes. 608. Why may we infer that animals are ignorant of the strength which they possess? Because if animals knew their strength, it would be impossible to harness the horse to a vehicle, or drive an ox to the slaughter. It is the fact of man being able to acquire knowledge, and animals being incapable, which gives the former that power over the latter by which their movements are made subservient to his will. 609. Why are the fiercer preying animals generally solitary in their habits? Because their nature, but for this instinct, would lead them to exert their combativeness upon each other, and so extinguish their own species. "So dismal and amazing a devastation, as in all the circum- Because, also, their chief purpose in creation seems to have been to act as checks upon the redundancy of other animals, or as scavengers clearing away the offal left upon the earth's surface. To this end their solitariness contributes by spreading their numbers over a wider surface, and with greater equality. 610. Why are carnivorous animals, and the larger quadrupeds, less prolific than other species of the animal kingdom? If the number of carnivorous animals were excessive, their rapacity would devastate the earth, while the larger quadrupeds would desolate the land by trampling down vegetation, and by the enormous quantity they would consume. 611. It should also be observed that these two classes have no natural enemies to contend with; the sanguinary character of the one, and the bulk of the other, securing them from violence. Of herbivorous and other animals essential to man, either as food, or for his other purposes, the increase is surprising, and exactly proportioned to his necessities and to the means the earth affords for their subsistence; and this rule applies equally to the wild districts, where the savage tribes, in supporting their existence, check the exuberance of what would otherwise be an evil rather than a blessing. 612. Why do animals usually seize their prey by the throat? Because their instinct guides them to select some vital part, or at all events some part where death can be caused in the most summary manner. The weasel tribe divide the blood-vessels in the side of the neck, even of animals much larger than themselves, with as much accuracy and precision as if they had carefully studied the anatomical structure of their prey; and though the larger cats throw themselves on the backs of those animals which they are unable to beat to the ground by the force of their spring, they tear the muscles of those parts on which the power of escape of their prey depends, and thus bring it most easily to the ground, when they speedily dispatch it, by lacerating the vital parts. |