278 Darwin, and after Darwin. 
cedent causation which serves as a condition to the 
process. Much more than half the battle would 
already have been won, had Darwin’s predecessors 
been able to explain the causes of Heredity and 
Variation; hence it is but a very partial victory 
which we have hitherto gained in our recent discovery 
of the effects of Struggle and Survival. 
Yet partial though it be in relation to the whole 
battle, in itself, or considered absolutely, there can be 
no reasonable doubt that it constitutes the greatest 
single victory which has ever been gained by the 
science of Biology. For this very reason, however, 
it behoves us to consider all the more carefully the 
extent to which it goes. But my discussion of this 
matter must be relegated to the next volume, where 
I hope to give abundant proof of the soundness of 
Darwin’s judgment as conveyed in the words:—“I 
am convinced that natural selection has been the main, 
but not the exclusive, means of modification.” 
