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Show 421 CONCLUDING REMARKS. CHAP. XXV lii. stock. It is improbable, if two men were to keep pigeons and act in this manner, that they would prefer exactly the same characters; they would, as we know, often prefer directly opposite characters, and the two lots would ultimately come to differ. 'rhis has actually occurred with strains or families of cattle, sheep, and pigeons, which have been long kept and carefully attended to by different breeders without any wish on their part to form new and distinct sub-breeds. This unconscious kind of selection wlll more especially come into acbon with animals which are highly serviceable to man; for every one tries to get the best clog, horse, cow, or sheep, and these animals will transmit more or less surely their good qualities to their offspring. Hardly any one is so careless as to breed from his worst animals. Even savages, when compelled from extreme want to kill some of their animals, would destroy the worst and preserve the best. With animals kept for use and not for mere amusement, different fashions prevail in different districts, leading to the preservation, and consequently to the transmission, of all sorts of trifling peculiarities of character. The same process will have been pursued with our fruit-trees and vegetables, for the best will always have been the most largely cultivated, and will occasionally have yielded seedlings better than their parents. The different strains, just alluded to, which have been raised by different breeders without any wish for such a result, and tbe unintentional modification of foreign breeds in their new homes, both afford excellent evidence of the power of unconscious selection. This form of selection has probably led to far more important results than methodical selection, and is likewise more important under a theoretical point of view from closely resembling natural selection. For during this process the best or most valued individuals are not separated and prevented crossing with others of the same breed, but are simply preferred and preserved; but this inevitably leads during a long succession of generations to their increase in number and to their gradual improvement; so that finally they prevail to the exclusion of the old parent-form. With our domesticated animals natural selection checks the production of races with any injurious deviation ot struc- CIIAP. XXVIII. CONCLUDING REMARKS. 425 ture. In the case of animals kept by savages and semi-civilised people, which have to provide largely for their own wants under different circumstances, natural selection will probably_ play a more important part. Hence such animals often closely resemble natural species. As there is no limit to man's desire to possess animals and plants more and more useful in any respect, and as the fancier always wishes, from fashion running into extremes, to produce each character more and more strongly pronounced, there is a constant tendency in every breed, through the prolonged action of methodical and unconscious selection, to become more and more different from its parent-stock; and when several breeds have been produced and are valued for different qualities, to differ more and more from each other. This leads to Divergence of Character. As improved sub-varieties and races are slowly formed, the older and less improved breeds are neglected and decrease in number. When few individuals of any breed exist within the same locality, close interbreeding, by lessening their vigour and fertility, aids in their final extinction. Thus the intermediate links are lost, and breeds which have already diverged gain Distinctness of Character. In the chapters on the Pigeon, it was proved by historical details and by the existence of connecting sub-varieties in distant lands that several breeds have steadily diverged in character, and that many old and intermediate sub-breeds have become extinct. Other cases could be adduced of the extinction of domestic breeds, as of the Irish wolf-dog, the old English hound, and of two breeds in France, one of which was formerly highly valued.4 Mr. Pickering remarks 5 that "the sheep figured on " the most ancient Egyptian monuments is unknown at the pre" sent day; and at least one variety of the bullock, formerly "known in Egypt, has in like manner become extinct." So it has been with some animals, and with several plants cultivated by the ancient inhabitants of Europe during the neolithic period. In Peru, Von Tschudi 6 found in certain tombs, apparently prior to the dynasty of the Incas, two kinds of maize not now known in the country. With our flowers and culinary vegetables, 4 M. Rufz de Lavison, in' Bull. Soc. Imp. d'Acclimat.,' Dec. 1862, p. 1009. 5 'Races of Man,' 1850, p. 315. 6 ' Travels in Peru,' Eng. translat., p. 177. |