The Mutation Hypothesis. 67 



the specific gradations become.^ We can obviously never 

 know how much more numerous, if at all, the mutations 

 have been than the species whose remains we find ; count- 

 less species may have arisen without leaving a trace 

 behind, but whether this is the result of the struggle 

 for existence, of natural selection, or of an advance in 

 a predetermined direction, cannot now be ascertained. 

 Phylogenetic changes make straight for the goal, seldom 

 swerving to the side, hardly ever advancing in a zigzag 

 line,^ but whether natural selection or variation in a 

 definite direction was the determining cause is obviously 

 a matter of personal opinion. 



The constancy of forms arising by mutation, as op- 

 posed to fluctuating variability, is supported by the re- 

 sults of paleontological research. Waagen as well as 

 Scott and others have declared against Wallace^s se- 

 lection theory on these grounds. They strongly maintain 

 that mutations must be admitted to a more prominent 

 place in any theory of evolution.^ Each ''mutation" 

 (elementary species) serves as a new center of analogous 

 variations. 



' Scott deduces from paleontological data a further 

 series of conclusions relative to the occurrence of muta- 

 tions. I find many of these views supported by a critical 

 study of the theory of variation as well as by my own 

 experimental work. I shall have to return to them at 

 the conclusion of tliis section, and in the first chapter 

 of the following one. 



Last year Korschinsky definitely expressed himself 

 as opposed to the present form of the selection theory. 



^Waagen, Benecke's Geogr. PaVdontol. Beitrage, II, S. 170. 

 * Scott, loc. cit., p. 370. 

 ^ Loc. cit., pp. 372, 27Z- 



