Seite - 54 - in The Origin of Species

54 ORIGIN OF SPECIES trict than in another, according to the state of civilisation of the inhabitants,—slowly to add to the characteristic features of the breed, whatever they may be. But the chance will be infinitely small of any record having been preserved of such slow, varying, and insensible changes. CIRCUMSTANCES FAVOURABLE TO MAN's POWER OF SELECTION I will now say a few words on the circumstances, favour- able, or the reverse, to man's power of selection. A high de- gree of variability is obviously favourable, as freely giving the materials for selection to work on; not that mere indi- vidual differences are not amply sufficient, with extreme care, to allow of the accumulation of a large amount of modifica- tion in almost any desired direction. But as variations mani- festly useful or pleasing to man appear only occasionally, the chance of their appearance will be much increased by a large number of individuals being kept. Hence, number is of the highest importance for success. On this principle Marshall formerly remarked, with respect to the sheep of parts of Yorkshire, "as they generally belong to poor people, and are mostly in small lots, they never can be improved." On the other hand, nurserymen, from keeping large stocks of the same plant, are generally far more successful than amateurs in raising new and valuable varieties. A large number of individuals of an animal or plant can be reared only where the conditions for its propagation are favourable. When the individuals are scanty, all will be allowed to breed, whatever their quality may be, and this will effectually prevent selec- tion. But probably the most important element is that the animal or plant should be so highly valued by man, that the closest attention is paid to even the slightest deviations in its qualities or structure. Unless such attention be paid nothing can be effected. I have seen it gravely remarked, that it was most fortunate that the strawberry began to vary just when gardeners began to attend to this plant. No doubt the straw- berry had always varied since it was cultivated, but the slight varieties had been neglected. As soon, however, as gar- deners picked out individual plants with slightly larger, ear- lier, or better fruit, and raised seedlings from them, and again