402 Darwin, and after Darwin, 
as they occur in organic nature. With the adapta- 
tions—if they can properly be so called—which occur 
in all the rest of nature,and which go to constitute the 
Cosmos as a whole so wondrous a spectacle of 
universal law and perfect order, this doctrine is but 
indirectly concerned. Nevertheless, it is of course 
fundamentally concerned with them to the extent that 
it seeks to bring the phenomena of organic nature into 
line with those of inorganic; and therefore to show 
that whatever view we may severally take as to the 
kind of causation which is energizing in the latter we 
must now extend to the former. This is usually 
expressed by saying that the theory of evolution by 
natural selection is a mechanical theory. It endea- 
vours to comprise all the facts of adaptation in organic 
nature under the same category of explanation as 
those which occur in inorganic nature—that is to 
say, under the category of physical, or ascertainable, 
causation. Indeed, unless the theory has succeeded 
in doing this, it has not succeeded in doing anything— 
beyond making a great noise in the world. If Mr. 
Darwin has not discovered a new mechanical cause in 
the selection principle, his labour has been worse than 
in vain. 
Now, without unduly repeating what has already 
been said in Chapter VIII, I may remark that, what- 
ever we may each think of the measure of success 
which has thus far attended the theory of natural 
selection in explaining the facts of adaptation, we ought 
all to agree that, considered as a matter of general 
reasoning, the theory does certainly refer to a vera 
causa of a strictly physical kind; and, therefore, that 
no exception can be taken to the theory in this respect 
