1 66 THE METHOD OF DARWIN. 



wherever variation offered the materials out of 

 which natural selection could produce it. 



The first thing to be established in proof of 

 the derivation of climbing plants from non- 

 climbers was the existence of gradations in the 

 power of climbing, and of intermediate stages 

 between the different methods of climbing, 

 by twining of the stem, by leaf-stalks, and by 

 tendrils; just as he connected the ocelli of the 

 peacock's tail by a series of gradations with 

 the more ordinary feather-markings of related 

 birds. But another unknown element was the 

 source of the variations upon which natural 

 selection could work to produce climbers. In 

 his arguments to prove his theories of descent 

 and natural selection Darwin showed that 

 variations do occur, and that when they occur 

 natural selection will inevitably preserve the 

 favorable and destroy the unfavorable. But he 

 could do little or nothing in the direction of 

 pointing out the cause of variations. He has 

 been incessantly twitted about this by his 

 opponents, especially because of the false 

 notion that he ascribed to chance all variations 

 whose causes were not known. Ignorance of 

 the sources of variation is no obstacle what- 

 ever to belief in Darwin's theories; but this 

 is true only when the species having a certain 



