DEVELOPMENT AND CREATION. 5 



the monistic development hypothesis, because it is the 

 one only scientific theory which rationally explains 

 the origin of organic species that is to say, by trans- 

 formation and reduces it to mechanical principles. 

 III. The theory of Selection or Darwinism is, up to 

 the present time, the most important of the various 

 theories which seek to explain the transformation of 

 species by mechanical principles, but it is by no 

 means the only one. If we assume that most species 

 have originated through natural elimination, we also 

 now know, on the other hand, that many forms 

 distinguished as varieties are hybrids between two 

 different varieties, and can be propagated as such ; and 

 it is equally well worthy of consideration that other 

 causes are in activity in the formation of species of 

 which, up to the present time, we have no conception. 

 Thus it is left to the judgment of individual naturalists 

 to decide what share is to be attributed to natural 

 selection in the origin of species, and even at the 

 present day authorities differ widely on the subject. 

 Some give it a large share, and some a very small one 

 in the result. Moritz Wagner, for instance, would 

 substitute his own migration-hypothesis for Darwin's 

 theory of selection ; while I regard the action of migra- 

 tion, which acts as isolation or separation, as merely 

 a special mode of selection. But these differing estim- 

 ates of Darwinism are quite independent of the absolute 



