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Show 192 SELECTION. CIIAP. XX. CHAPTER XX. SELECTION BY MAN. SELECTION A DIFFTCn,T ART- :r.mTHODICAL, UNCONSCIOUS, AND NATURAL SELECTION _ RE TILTS OF UETflODICAL SELECTION- CAHE TAKEN IN SELECTION- SELECTION WITH PLA:ti~S- SELECTION CARRillD ON BY TilE ANCillNTS, AND BY SE1t1I-CIVILISED PEOPLE - l'NU!PORTANT CIIARACTERS OFTEN A'l'TENDED TO - "L""NCONSCIOUS SELECTION- AS CIRCUMSTANCES SLOWLY CHANGE, SO JIA \E OUR DOllillSTICATED ANIMALS CHANGED THROUGH THE AC'l'ION OF UNCONSCIOUS SELEC'l'JON - INFLUENCE OF DIFFERENT BREEDERS ON THE SAJ\ffi SC.I:I-VAI!lE'l'Y- PLANTS AS AFFECTED BY UNCONSCIOUS SELECTION - EFFECTS OF SELECTION AS SHOWN BY THE GREAT AMOUNT OF DIFFEHENCE IN Tim PARTS MOST \ALUED BY JITAN. THE power of Selection, whether exercised by man, or brought into play under nature through the struggle for existence and the consequent survival of the fittest, absolutely depends on the variability of organic beings. vVithout variability nothing can be effected ; slight individual differences, however, suffice for the work, and are probably the sole differences which are effective in the production of new species. Hence our discussion on the causes and laws of variability ought in strict order to have preceded our present subject, as well as the previous subjects of inheritance, crossing, &c. ; but practically the present arrangement has been found the most convenient. lVIan does not attempt to cause variability; though he unintentionally effects this by exposing organisms to new conditions of life, and by crossing breeds already formed. But variability being granted, he works wonders. Unless some degree of selection be exercised, the free commingling of the individuals of the same variety soon obliterates, as we have previously seen, the slight differences which may arise, and gives to the whole body of individuals uniformity of character. In separated districts, long-.continued exposure to different conditions of life may perhaps produce new races without the aid of selection; but to this difficult subject C IIAP. XX. SELECTION. 193 of the direct action of the conditions of life we shall in a future chapter recur. vVhen animals or plants are born with some conspicuous and firmly inherited new character, selection is reduced to the preservation of such individuals, and to the subsequeut prevention of crosses; so that nothing more need be said on the subject. But in the great majority of cases a new character, or some superiority in an old character, is at first faintly pronounced, and is not strongly inherited; and then the full difficulty of selection is experienced. Indomitable patience, the finest powers of discrimination, and sound judgment must be exercised during many years. A clearly predetermined object must be kept steadily in view. Few men are endowed with all these qualities, e~pecially with that of discriminating very slight differences; judgment can be acquired only by long experience ; but if any of these qualities be wanting, the labour of a life may be thrown away. I have been astonished when celebrated breeders, whose skill and judgment have been proved by their success at exhibitions, have shown me their animals, which appeared all alike, and have assigned their reasons for matching this and that individual. The importance of the great principle of Selection mainly lies in this power of selecting scar9eJy appreciable differences, which nevertheless are found to be transmissible and which can be accumulated until the result is made manifes~ to the eyes of every beholder. The principle of selection may be conveniently divided into three kinds. Methodical selection is that which guides a man who systematically endeavours to modify a breed according to some predetermined standard. Unconscious selection is that which follows from men naturally preserving the most valued and destroying the less valued individuals, without any thought of alteril).g the breed; and undoubtedly this process slowly works great changes. Unconscious selection graduates in~,9 methodical, and only extreme cases can be distinctly separated; for he who preserves a useful or perfect animal will general1y breed from it with the hope of getting offspring of the same character; but as long as he has not a predetermined purpose to improve the breed, he may be said to be selecting VOL. II. 0 |
