SUMMAR Y. 51 



The sub-groups are called varieties, and are every- 

 where regarded as genetically related to each other. 

 The question then arises as to whether there is a 

 limit to this accumulation of variations. It is 

 claimed by evolutionists that there is no limit ex- 

 cept that set by physical conditions. They continue 

 to increase, causing the varieties to become more 

 and more unlike, until they finally become so different 

 that cross-breeding becomes no longer possible in all 

 cases. Thus individual variations become varieties; 

 and varieties become species. But it has not yet 

 been found possible to prove this claim by direct 

 evidence. For it is asserted on the other hand that 

 these variations are not accumulated indefinitely, 

 but are confined within certain bounds. The limits 

 thus assumed are supposed to constitute boundary 

 lines between species. In attempting to define these 

 specific limits, it has been found impossible to dis- 

 cern them in any amount of structural difference. 

 The differences between true varieties may surpass 

 those between species. Such a limit has been drawn 

 at the point of sterility, the position being taken 

 that no amount of ordinary variation can cause the 

 varieties thus arising to become mutually sterile. 

 The evolutionists have been unable to disprove this 

 claim by direct evidence, for they can cite no in- 

 stances where varieties have become unfertile. But 

 they deny the correctness of this definition, showing 

 that sterility is not a rigid bar separating species, since 

 in some cases true species are fertile when crossed ; 

 they have further given reason for believing that 

 sterility is caused by differences in the sexual organs. 



