ZOOGENESIS 



very first been essentially the same? The probabili- 

 ties are in favor — overwhelmingly in favor — of the 

 simultaneous development of some representative or 

 representatives of all, or practically all, of the phyla 

 or major groups of animals at the time of the very 

 first appearance of life. 



The only acceptable hypothesis is that in its broader 

 features the development of animal forms took place 

 by concurrent evolution. 



All of the actual evidence we have supports this 

 supposition. This evidence comes from the fossils 

 that we find in the very earliest rocks wherein fossils 

 are satisfactorily preserved. Practically all these fos- 

 sils are more or less widely different from the corre- 

 sponding animals we know today. But we recognize 

 them for what they are because they fall within the 

 definitions of their respective groups, and these defini- 

 tions are drawn up from a study of their living repre- 

 sentatives alone. 



The recognition of these fossils as members of cer- 

 tain groups through the application of definitions 

 based on living animals alone means that from the 

 very earliest times of which we have a record the 

 broader features of the animal life upon the earth have 

 remained unchanged. So from all the tangible evi- 

 dence that we have been able to discover we are forced 

 to the conclusion that all the major groups of animals 

 at the very first held just about the same relation to 

 each other that they do today. 



How may the simultaneous appearance of all the 

 major groups of animals be harmonized with their 



