76 ORGANIC EVOLUTION' CONSIDERED 



This has commonly been regarded as a well-defined 

 distinction between varieties and species. 



If the varieties of pigeons which are so different 

 from each other did not freely cross, and if the mon- 

 grel offspring were not fertile, his argument as to the 

 production of new species under domestication would 

 be complete. 



The fact is, we do not know of the origin of any two 

 species of animals that do not cross and whose off- 

 spring are not fertile; in other words, we do not 

 know of the origin of species, but only of varieties. 

 The origin of species that will not cross and produce 

 fertile offspring is assumed from the origin of varie- 

 ties that do cross and produce fertile offspring. 



This leaves the evolutionist to account for one of 

 the most difficult things in connection with his theory, 

 namely, how did varieties of animals of the same 

 species become cross-sterile? Let us consider this 

 difficulty. 



It is claimed by evolutionists that varieties are 

 incipient species ; that closely related existing species 

 were once only varieties of the same species. These 

 closely related species which, it is claimed, have had 

 a common origin, now often live side by side, occupy- 

 ing the same or contiguous territories. 



It is a well known fact that by crossing varieties the 

 offspring are rendered more vigorous and fertile, 

 while by crossing species the offspring are either 

 sterile or become so in a few generations and die out. 

 How can varieties that are perfectly cross-fertile 

 become species that are cross-sterile? 



Suppose that a species A, in a state of nature, pro- 

 duces a variety B, the known facts lead us to believe 

 that A and B would cross with each other, and that B 

 would be lost as a variety. It is admitted by evolu- 

 tionists that if the closely related varieties of domes- 



