7yS Darwin, and after I arzvin. 



cedent cau'^ation 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 conve}^ed in the words : — " I 

 am convinced that natural selection has been the main, 

 but not the exclusive, means of modification." 



