282 Darwin, and after Darwin. 



various mechanisms in question have themselves had 

 a history beginning in the forms of most uniformity 

 and simplicity, gradually advancing to forms more 

 varied and complex, nowhere exhibiting any inter- 

 ruptions in their upward progress, until the world of 

 organic machinery as we now have it is seen to have 

 been but the last phase of a long and gradual growth, 

 the ultimate roots of which are to be found in the soil 

 of undifferentiated protoplasm. 



Lastly, when there is supplied to us the suggestion 

 of natural selection as a cause presumably adequate to 

 account for this continuous growth in the number, the 

 intricacy, and the perfection of such mechanisms, it is 

 only the most unphilosophical mind that can refuse to 

 pause as between the older hypothesis of design and 

 the newer hypothesis of descent. 



Thus it is clear that the a priori standing of the 

 rival hypotheses of naturalism and supernaturalism in 

 the case of all these pieces of organic machinery, is 

 profoundly affected by the question whether they came 

 into existence suddenly, or whether they did so grad- 

 ually. For, if they all came into existence suddenly, 

 the fact would constitute well-nigh positive proof 

 in favour of supernaturalism, or creation by design ; 

 whereas, if they all came into existence gradually, this 

 fact would in itself constitute presumptive evidence in 

 favour of naturalism, or of development by natural 

 causes. And, as shown in the previous chapters, 

 the proof that all species of plants and animals came 

 into existence gradually or the proof of evolution as 

 a fact is simply overwhelming. 



From a still more general point of view I may state 

 the case in another way, by borrowing and somewhat 



