Darwin's Artificial and Natural Selection 97 



reached, as shown by De Vries's experiments with clover, 

 and it is always possible that a definite variation of the 

 right sort may arise at any stage of the process. If this 

 should occur, then a new standard is introduced from which, 

 as from a new base, variations fluctuating in the desired 

 direction may be selected. 



This question, before all others, ought to be settled before 

 we begin to speculate further as to what selection is able 

 to accomplish. 



Darwin's theory is often stated in such a general way 

 that it would be applicable to either sort of variation ; but 

 if definite variation can go on accumulating without selec- 

 tion, then possibly we could account for evolution without 

 supposing any other process to intervene. Under these 

 circumstances all that could be claimed for selection would 

 be the destruction of those variations incapable of living, 

 or of competing with other forms. Hence the process of 

 selection would have an entirely negative value. 



The way in which domesticated animals and plants have 

 originated is explained by Darwin in the following significant 

 passage : — 



" Let us now briefly consider the steps by which domestic 

 races have been produced, either from one or from several 

 allied species. Some effect may be attributed to the direct 

 and definite action of the external conditions of life, and 

 some to habit ; but he would be a bold man who would 

 account by such agencies for the differences between a dray- 

 and race-horse, a greyhound and bloodhound, a carrier and 

 tumbler pigeon. One of the most remarkable features in 

 our domesticated races is that we see in them adaptation, 

 not indeed to the animal's or plant's own good, but to man's 

 use or fancy. Some variations useful to him have probably 

 arisen suddenly, or by one step ; many botanists, for instance, 

 believe that the fuller's-teasel, with its hooks, which cannot 

 be rivalled by any mechanical contrivance, is only a variety 



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