232 Experimental Zoology 



The Selection Theory and the Theory oj the Survival oj Mutations 



The differences between the Darwinian theory oj natural selec- 

 tion and the theory oj the survival oj mntations have been already 

 indicated in their main features. It remains only to clear up 

 certain minor points. 



Darwin has stated his theory in such general terms that it 

 may easily be supposed to cover also the theory of the survival of 

 mutations. In fact, he does at times include the latter view in 

 his theory of survival ; for he beheved that competition and sur- 

 vival take place not only between the individuals of a species 

 (fluctuating or individual variations), but also between varieties 

 and species themselves. The latter is, in principle, nothing 

 more than the theory of the survival of the better-adapted ele- 

 mentary species. In this regard we are at one with Darwin's 

 view. But in the application of the Darwinian theory both by 

 Darwin himself, and especially by his followers, the whole weight 

 of the argument has been thrown in favor of the selection of 

 fluctuating variations. Moreover, although Darwin was perfectly 

 familiar with the occurrence of sports, mutations, and saltations, 

 he has argued at times that the latter cannot have given the basis 

 for the evolution of wild species, because the laws of hybridiza- 

 tion that govern the crosses between wild species and varieties 

 differ from the laws of hybridization in the case of sports. 



Danvin's theory dealt with the ''origin oj species,'^ and the 

 theory of natural selection was offered to account for the origin 

 of species through the selection of fluctuation variations. Many 

 cases are given in which it is attempted to show how individual 

 differences become built up into varietal differences, and the 

 latter into specific differences. In sharp contrast to this view the 

 other theory, the theory of the survival of mutations, affirms that 

 species do not originate in this way. Individual differences do 

 not slowly change into specific differences. Specific differences 

 appear suddenly as mutations. The origin of species thus be- 

 comes a very different question from that imagined on Darw^in's 

 theory of selection. On the mutation theory selection destroys 



