232 Experimental Zovlogy 
The Selection Theory and the Theory of the Survival of Mutations 
The differences between the Darwinian theory of natural selec- 
tion and the theory of the survival of mutations 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 believed 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. 
Darwin’s theory dealt with the ‘‘origin of 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 Darwin’s 
theory of selection. On the mutation theory selection destroys 
