PRINCIPLE OF NATURAL SELECTION. 22$ 



made. There was an intellectual explosion, a 

 flash of the mind, and from that moment his 

 life-work was devoted to elaborating the conse- 

 quences of the principle. The facts which he 

 had been gathering and reflecting upon were 

 explained as the effects of the cause which 

 Malthus presented, and gathered a new sig- 

 nificance from it. 



" Here, then, I had at last got a theory by 

 which to work," he said. The groping was at 

 an end. His future work was outlined. The 

 confession in that sentence can be appreciated 

 only by one who has in his own experience 

 passed from the mental strain and perplexity 

 of a purely inductive effort to the solid ground 

 afforded by even a fairly probable hypothesis. 

 Doubtless his work was thenceforth many times 

 more rapid than it could otherwise have been; 

 for with so vast a number of facts to be con- 

 sidered the theory itself was the only pathfinder. 

 Only after the discovery of the principle could 

 the work of gathering up and classifying known 

 facts and of searching for new ones, of reducing 

 exceptions and apparently unexplainable groups 

 of facts, go on apace. The logical process by 

 which adaptations, variations, and the struggle 

 for existence were brought together into the 

 relation of cause and effect was deductive; and 



