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SELECTION. Chap. XXI. 



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wherever selection is not practised, distinct races are not formed. 

 When any one part of the body or quality is not attended 

 to, it remains either unchanged or varies in a fluctuating manner, 

 whilst at the same time other parts and other qualities may 

 become permanently and greatly modified. But from the ten- 

 dency to reversion and to continued variability, those parts or 



which are now undergoing rapid improvement through 



selection, are likewise found to vary much. Consequently 

 highly-bred animals, when neglected 













soon degenerate ; but we 



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have no reason to believe that the effects of long-continued 

 selection would, if the conditions of life remained the same be 

 soon and completely lost. 



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Man always tends to go to an extreme point in the selection 

 whether methodical or unconscious, of all useful and pleasing 

 qualities. This is an important principle, as it leads to con- 

 tinued divergence, and in some rare cases to convergence of 

 character. The possibility of continued divergence rests on 

 the tendency in each part or organ to go on varying in the 

 same manner in which it has already varied; and that this 

 occurs, is proved by the steady and gradual improvement of 

 many animals and plants during lengthened periods. The prin- . 

 ciple of divergence of character, combined with the neglect and 

 final extinction of all previous, less-valued, and intermediate 

 varieties, explains the amount of difference and the distinct- 

 ness of our several races. Although we may have reached the 

 utmost limit to which certain characters can be modified, yet 

 we are far from having reached, as we have good reason to 

 believe, the limit in the majority of cases. Finally, from 

 the difference between selection as carried on by man and by 

 nature, we can understand how it is that domestic races often, 

 though by no means always, differ in general aspect from closely 

 allied natural species. 



Throughout this chapter and elsewhere I have spoken of 

 selection as the paramount power, yet its action absolutely 

 depends on what we in our ignorance call spontaneous or acci- 

 dental variability. Let an architect be compelled to build an 

 edifice with uncut stones, fallen from a precipice. The shape 

 of each fragment may be called accidental; yet the shape of 

 each has been determined by the force of gravity, the nature 











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