§&! ZOOGENESIS Wii 



animal type subtraction has already progressed almost 

 to the extreme limit compatible with existence so 

 there remains very little that can be taken away with- 

 out endangering the life of the individual. Natu- 

 rally, therefore, the mutants with which we are 

 familiar at the present day differ relatively little from 

 the usual type. Yet rhinoceros mice, hairless dogs 

 and horses, and many other unusual creatures, show 

 how it is quite possible for new species and even 

 genera to appear in such a fashion as to give but 

 little indication of their immediate ancestry. 



As we go further and further back in geological 

 time we find ourselves among the ancestral forms from 

 which the present highly specialized animals were 

 descended. The ancestral form from which any as- 

 semblage of animals is descended combines the char- 

 acters which are selectively distributed among the 

 descendants. For instance, in the ancestral wolf there 

 are combined all of the features which now are widely 

 distributed among the various breeds of domestic 

 dogs. Our different breeds of dogs differ from each 

 other not in the appearance of any new characters, 

 but in the selective suppression of characters through 

 which one or more special features are made to stand 

 out prominently. 



The more well developed structural characters there 

 are in any animal type — in other words the better 

 and more complete the structural balance — the greater 

 is the possibility for the appearance of many widely 

 different economically successful mutants among its 

 descendants. 



[2-19] 



