46 CIRCUMSTANCES FAVOURABLE. [Chap. L 



other, according to the state of civilisation of the in- 

 habitants,— 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, 

 favourable, , or the reverse, to man's power of selection. 

 A high degree of variability is obviously favourable, as 

 freely giving the materials for selection to work on; 

 not that mere individual difEerences are not amply 

 sufficient, with extreme care, to allow of the accumula- 

 tion of a large amount of modification in almost any 

 desired direction. But as variations manifestly 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. 

 ■WTien the individuals are scanty, all will be allowed to 

 breed, whatever their quality may be, and this will 

 effectually prevent selection. But probably the most 

 important element is that the animal or plant should 



