I nJierilance of Quanlilaliue Characters 77 



This conception of cumulative factors, therefore, 

 has far-reaching significance. For a long time, biologists 

 have recognized individual quantitative variation within 

 the species. Darwin depended upon it as the basis of 

 his theory of evolution; in fact, ever since Darwin's 

 Origin of species, individual variation has been funda- 

 mental in our conceptions. To account for this univer- 

 sally recognized phenomenon, Darwix proposed his 

 transportation hypothesis and Weismann offered his 

 germinal selection, both of which were unsatisfactory 

 explanations. Aside from these two attempts to explain 

 individual variation, no other comprehensive scheme 

 had been presented. Biologists had simply recognized 

 the fact of individual variation without any clear con- 

 ception of the mechanism. 



The importance of this new theory, therefore, is 

 obvious. It is an ingenious explanation of the inherit- 

 ance of quantitative characters and of the existence of 

 individual variations. Furthermore, the theory has 

 not been developed through meditation, but has its 

 basis in scientific experiments. It is imaginative to a 

 certain extent, as is every other valuable theory, but 

 unlike most such theories, it has a substantial foundation, 

 namely, Mendel's law. 



The importance of the possible role of cumulative 

 factors in explaining individual variation, which in 

 turn may be the basis of a certain type of evolution, 

 has been emphasized because its importance has 

 perhaps not yet been sufliciently appreciated. It 

 promises to be one of the most important theories of 

 biology, but of course will bear further testing by in- 

 vestigators. 



