234 SELECTION. Chap. XXL 



descended from a common progenitor, and lie in his turn will 

 perhaps reject the notion with scorn. Thus the naturalist 

 and breeder may mutually learn a useful lesson from 'each 

 other. 



Summary on Selection by Man. — There can he no doubt that 

 methodical selection has 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 circumstances have slowly changed, which many animals 

 have undergone in the same country, or when transported 

 into a foreign land. We see the combined effects of methodi- 

 cal and unconscious selection, in the great amount of 

 difference in those parts or qualities which are valued by man 

 in comparison with the parts which are not valued, and 

 consequently Lave 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 could not 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 

 variability; and this is mainly caused, as we shall hereafter 

 see, by changes in the conditions of life. Selection is some- 

 times rendered 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 inter- 

 breeding. That methodical selection 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 



