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Show RO NA'fURAL SELECTION. [CHAP. IV. selected character is fully exercised by her ; and the being is placed under well-suited conditions of life. Man keeps the natives of many climates in the same. country; he s~ldoln exercises each selected character In some pecuhar and fitting manner; he feeds a long and a short-beaked pigeon on the same food ; he does not exercise a longbacked or long-legged quadruped in any peculiar manner; he exposes sheep with long and short wool to the same clilnate. He does not allow the most vigorous males to struggle for the females. He does not rigidly destroy all inferior animals, but protects during each varying season, as far as lies in his power, all his productions. He often begins his selection by some half-monstrous form; or at least by some modification prominent enough to catch his eye, or to be plainly useful to him. Under nature, the slightest difference of structure or constitution may well turn the nicely-balanced scale in the struggle for life, and so be preserved. I-Iow fleeting are the wishes and efforts of n1an! how short his time ! and consequently how poor will his products be, compared with those accumulated by nature during whole geological periods. Can we wonder, then, that nature's productions should be far " truer" in character than man's productions; that they should be infinitely better adapted to the most complex conditions of life, and should plainly bear the stamp of far higher workmanship? It may be said that natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life. We see nothing of these slow changes in pro.gress, until the hand of time has marked the long lapse of ages, and then so imperfect is our view into long past geological ages, that we only see that the forms of life are now different from what they formerly were. Although natural seiection can act only through and for the good of each being, yet characters and structures, CHAP. IV.] NATURAL SELECTION. 81 which we are apt to consider as of very trifling importance, may thus be acted on. When we see leaf-eating insects green, and bark-feeders mottled-grey; the alpine ptarmigan white in winter, the red-grouse the colour of heather, and the black-grouse that of peaty earth, we must believe that these tints are of service to these birds and h1sects in preserving then1 from danger. Grouse; if not destroyed at some period of their lives, would increase in e?untless numbers; they are known to suffer largely from b1rds of prey; and hawks are guided by eyesight to their prey,-so much so, that on parts of the Continent persons are warned not to keep white[igeons, as being the most liable to destruction. Hence can see no reason to doubt that natural selection might be most effective in giving the proper column to each kind of grouse, and in keeping that colour, when once acquired, true and constant. Nor ought we to think that the occasional destruction of an animal of any particular colour would produce little effect ! we should remember how essential it is in a flock of white sheep to destroy every lamb with the faintest trace of black. In plants the down on the fruit and the colour of the flesh are considered by botanists as characters of the most trifling importance : yet we hear from an excellent horticulturist, Downing, that in the United States smooth-skinned fruits suffer far more from a beetle a curculio, than those with down; that purple plum~ suffer far more from a certain disease than yellow plums· whereas another disease attacks yellow-fleshed peaches fa;. more. than those with. other. coloured flesh. If, with all the aids of art, these shght differences make a great difference in cultivating the several varieties, assuredly, in a state of nature, where the trees .would have to struggle with other trees, and with a host of enemies, such differences would effectually settle which variety, whether a smooth or downy, a yellow or purple fleshed fruit, should succeed. In looking at many small points of difference between species, whicli, as far as our ignorance permits us to judge, se.em to be quite unimportant, we must not forget that chmate, food, &c., probably produce some slight and direct effect. It is, however, far more necessary to bear in 4* |
