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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