EVOLUTION AND MUTATION 9 



forth this same view. According to his conception, species 

 are derived from one another by small shocks. Each 

 shock caused the old limits to be transgressed; but, after 

 it, the new species remained unchanged until, perhaps after 

 centuries, a new shock made it transgress its new limits. 

 Each single type (be it species, subspecies, or variety) is 

 thus wholly constant from its first appearance and until the 

 time it disappears, either after, or without, the production 

 of daughter species. 



On the ground of the mutation theory, there is a struggle 

 for Hfe among species as well as among individuals. There 

 is selection, also, between competing species and among 

 the individuals of the same species; the fittest will survive, 

 but this holds good for species as well as for individuals. 

 As to individuals, natural selection may, to some extent, 

 cause a divergence from the average type. But among 

 species, natural selection is the most potent factor, since it 

 eliminates some and thereby protects and favors others. 

 Thus we come to the conclusion that natural selection is 

 as active as Darwin assumed it to be, and is as pre-eminent 

 a factor in the process of evolution. It causes the survival 

 of the fittest; but it is not the survival of the fittest individ- 

 uals, but that of the fittest species, by which it guides the 

 development of the animal and vegetable kingdoms. 



Summing up the main points of this discussion, we may 

 sketch the origin of species, according to the theory of mu- 

 tation, in the following manner. Species are derived from 

 other species by means of sudden small changes which, in 

 some instances, may be scarcely perceptible to the inexper- 

 ienced eye. From their first appearance they are uniform 

 and constant, when propagated by seed; they are not con- 

 nected with the parent species by intermediates and have 

 no period of slow development before they reach the full 

 display of their characters. They do not always arise, but 



