84 HEREDITY AND VARIATION 



Even when this theory is strengthened by subsidiary theories, 

 e.g. as to the efficacy of isolation and germinal selection, it is 

 more theoretically than practically convincing. It places such a 

 heavy burden on the shoulders of Natural Selection that the idea 

 of a leaping instead of a creeping Proteus has always been 

 welcome. 



But why are evolutionists now entertaining an idea — the 

 importance of discontinuous variations — which Darwin con- 

 sidered and then rejected ? The answer is that we now know 

 of many instances of discontinuous variation in animals, 

 and even more among plants, that we have some good 

 evidence of these discontinuous variations or mutations 

 " breeding true," and that we have in the theory of Mendelian 

 inheritance a reason why a mutation which has once arrived 

 should persist. 



Some modern authorities go the length of saying that 

 "mutations" form the sole raw material of evolution, and that 

 " individual fluctuations " do not count at all. This seems an 

 illustration of the common tendency to take up an extreme 

 position in the enthusiasm of a new discovery. Because dis- 

 continuous variations are common and important it does not 

 follow that continuous fluctuations are of no moment. Those 

 " whose humour is nothing but mutation " confess that it is 

 very difficult to distinguish between a small mutation and a 

 large fluctuation. If the large fluctuation be heritable — which 

 we may assume until it has been disproved — we confess that we 

 do not see what is gained by trying to distinguish it from a small 

 mutation. 



The New View. — Dominated by the idea that " organisms 

 are mere conglomerates of adaptative devices," and that these 

 patents cannot but be the outcome of slow accumulation of 

 minute fluctuations under the directive agency of selection, 

 naturalists have paid little heed to the open secret that the 

 living creature is inherently a Proteus suddenly and discon- 





