Chap. XXI. SELECTION. 247 



methodical selection lias effected and will effect wonderful 

 results. It was occasionally practised in ancient times, and 

 is still practised by semi-civilised people. Characters of the 

 highest importance, and others of trifling value, have been 

 attended to, and modified. I need not here repeat what has 

 been so often said on the part which unconscious selection has 

 played : we see its power in the difference between flocks which 

 have been separately bred, and in the slow changes, as circum- 

 stances have slowly changed, which many animals have under- 

 gone in the same country, or when transported into a foreign land. 

 We see the combined effects of methodical and unconscious selec- 

 tion in the great amount of difference between varieties in those 

 parts or qualities which are valued by man, in comparison with 

 those which are not valued, and consequently have not been 

 attended to. Natural selection often determines man's power 

 of selection. We sometimes err in imagining that characters, 

 which are considered as unimportant by the systematic naturalist, 

 could not be affected by the struggle for existence, and there- 

 fore be acted on by natural selection ; but striking cases have 

 been given, showing how great an error this is. 



The possibility of selection coming into action rests on varia- 

 bility ; and this is mainly caused, as we shall hereafter see, by 

 changes in the conditions of life. Selection is sometimes ren- 

 dered difficult, or even impossible, by the conditions being opposed 

 to the desired character or quality. It is sometimes checked by 

 the lessened fertility and weakened constitution which follow 

 from long-continued close interbreeding. That methodical selec- 

 tion may be successful, the closest attention and discernment, 

 combined with unwearied patience, are absolutely necessary ; 

 and these same qualities, though not indispensable, are highly 

 serviceable in the case of unconscious selection. It is almost 

 necessary that a large number of individuals should be reared ; 

 for thus there will be a fair chance of variations of the desired 

 nature arising, and every individual with the slightest blemish 

 or in any degree inferior may be freely rejected. Hence length 

 of time is an important element of success. " Thus, also, propa- 

 gation at an early age and at short intervals favours the work. 

 Facility in pairing animals, or their inhabiting a confined area, 

 is advantageous as a check to free crossing. Whenever and 



