i io MEMORIAL SKETCH. 



But it is further obvious that Natural Selection can only 

 operate where a capacity for variation is inherent in the type. 

 There are some types of which the range of variation is so 

 restricted that they can only exist at all under certain combina 

 tions of conditions ; their distribution, therefore, being limited 

 alike in space and in time. There are others which have a 

 much wider range, being able to adapt themselves to great 

 diversities in external conditions; but it cannot be justly said 

 that the variations which these present are &quot; spontaneous.&quot; 

 Every effect requires a cause. Natural Selection is assuredly 

 not that cause, since its effect is only to perpetuate, among 

 varietal forms, that one which best suits the conditions of exist 

 ence. Consequently we must look io forces acting either within 

 or without the organism, as the real agents in producing what 

 ever developmental variations it may take on. Of the action of 

 such forces, we at present know scarcely anything; and Mr. 

 Darwin has not given us much help towards the solution of the 

 problem.* But this much seems to me clear : that just as there 

 is at the present time a determinate capacity for a certain fixed 

 kind of development in each germ, in virtue of which one 

 evolves itself into a zoophyte, and another (though not originally 

 distinguishable from it) into a man, so must the primordial 

 germs have been endowed each with its determinate capacity 

 for a particular course of development ; in virtue&quot; of which it 

 has evolved the whole succession of forms that has ultimately 

 proceeded from it. That the &quot; accidents &quot; of Natural Selection 

 should have produced that orderly succession, is to my own mind 

 inconceivable ; I cannot but believe that its evolution was part 

 of the original Creative Design ; and that the operation of 

 Natural Selection has been simply to limit the survivorship, 

 among the entire range of forms that have thus successively 

 come into existence, to those which were suited to maintain that 

 existence at each period. 



* In 1882 this last clause ran thus : &quot;But Mr. Darwin has himself most 

 &quot; fully recognized the need of them. His latest utterance on the subject is that 

 * at the present time there is hardly any question in biology of more import- 

 ance than that of the nature and causes of variability. I cannot, then, be 

 &quot; accused of undervaluing I &amp;gt;arwin s work, in pointing out that what I originally 

 &quot;iclt to be its weakest part, still remains incomplete.&quot; 



