118 Evolution and Adaptation 
dependently of the change of climate itself, would seriously 
affect the others... . In such cases, slight modifications, 
which in any way favored the individuals of any species, by 
better adapting them to their altered conditions, would tend 
to be preserved ; and natural selection would have free scope 
for the work of improvement.” 
The first half of the first of these two quotations seems so 
plausible, that without further thought we may be tempted 
to give a ready assent to the second, yet the whole issue is 
contained in this statement. In the abstract, it undoubtedly 
appears true that any slightly useful modification might tend 
to be preserved. Whether it will, in reality, be preserved 
must depend on many things that should be taken into 
account. This question will come up later for further con- 
sideration; but it should be pointed out here, that, even 
assuming that one or more individuals happen to possess a 
favorable variation, it by no means follows that natural 
selection would have free scope for the work of improvement, 
because the question of the inheritance of this variation, 
and of its accumulation and building up through successive 
generations, must be determined before we can be expected 
to give assent to this argument, that appears so attractive 
when stated in an abstract and vague way. 
Darwin again makes the statement that under the term 
variation it must never be forgotten that mere individual 
differences are meant. “As a man can produce a great 
result with his domestic animals and plants by adding up in 
any given direction individual differences, so could natural 
selection, but far more easily from having incomparably 
longer time for action.” Too much emphasis cannot be laid 
on the fact that Darwin believed that selection takes place 
amongst the small individual differences that we find in 
animals and plants. Some of his followers, as we shall see, 
are apt to put into the background this fundamental con- 
ception of Darwin’s view. His constant comparison between 
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