OTHER THEORIES OF SPECIES-FORMING. 363 



posed to have been produced by this process, it is more probable 

 that the result obtained represents the summation of a series of 

 mutations rather than of a series of ordinary fluctuating variations. 

 For mutations are permanent: variations transitory" (Castle, p. 



524). 



"It is to my mind impossible to find any support for a theory of 

 evolution by minute changes from the study of anatomical varia- 

 tions. I should not venture to say, on the other hand, that they 

 give any direct support to the theory of mutation : but, at least, they 

 are not in disaccord with it" (Dwight, p. 532). 



"It seemed necessary to discuss ethological characters at some 

 length for the purpose of vindicating their importance. Having 

 attempted this, I may say that these characters seem to me to offer 

 even fewer difficulties than the morphological characters to the 

 acceptance of the mutation theory, for the reason that the ethological 

 and psychological processes are conceived primarily as qualities 

 and not quantities. Thus the psychical elements, i. e., the simple 

 feelings, cravings, and sensations, are disparate qualitative processes 

 which cannot be derived from one another or from some more 

 undifferentiated process. This is still more evident in the case of the 

 complex psychical phenomena. Similarly, instincts, with which 

 ethology is most concerned, when resolved into their simplest com- 

 ponents are seen to consist of discrete reactions which cannot be 

 shown to arise from one another. Although, on the other hand, 

 the measurable intensities and durations of the reactions are anal- 

 ogous to the fluctuating structural variations, it is even more difficult 

 for the psychologist to conceive of a particular feeling, craving, 

 or sensation as arising from the greater or less intensity or dura- 

 tion of some other psychic process, than it is for the morphologist 

 to conceive of the origin of new characters from the fluctuating 

 variations of structure" (Wheeler, p. 539). 



"Mutation is even more urgently demanded for the explanation 

 of many other instincts, especially those of symbiotic and parasitic 

 species and of species with profound and sudden metamorphosis. 

 In these cases, a particular activity, on which most often depends 

 the life of the individual or of its progeny, has to be performed 

 with a high degree of proficiency at its very phylogenetic incep- 

 tion or it can be of no advantage to the individual or the race. 

 Such cases, with which you are all familiar, have ever been the 

 insurmountable obstacle to the evolution of instincts on the theory 

 of fluctuating variations and natural selection. The theory of 

 organic selection seems to me merely to conceal but not to over- 

 come the difficulties. The mutation theory frankly avoids the diffi- 

 culties even if it fails to throw any light on the origin of the muta- 



