'^'^'^ THE NEW EVOLUTION '^^'^ 



multicellular types which we know today, is ex- 

 plained by what is called the theory of evolution. 



Evolution as commonly understood assumes the 

 gradual development step by step of all the widely 

 varying forms of animal life from an original form 

 of simple structure. But the developmental course 

 which has been followed by animal life cannot be 

 reduced to any such simple formula. In the first 

 place, the study of animal life itself, whether the 

 study of adult forms or of embryology, shows it to be 

 wholly incapable of such simple interpretation. In 

 the second place, this hypothesis is not in accord with 

 the fossil history of animals as we know it. In the 

 third place, it is not in accord with our interpretation 

 of the geological processes and conditions in the very 

 distant past. 



Any acceptable theory of animal development must 

 be in complete agreement with its setting. It must 

 take into account the geological background and 

 must be in accord with what we know, or believe, to 

 have been the condition of the earth in the very 

 distant past. 



In tracing the history of animal life from its very 

 first appearance to the infinite complexity which we 

 see at the present day there are three entirely separate 

 sets of facts to be considered, and any acceptable 

 theory of the development of animal life must har- 

 monize and correlate all three. 



In the first place, within each of the so-called phyla 

 or major groups of animals, as is well seen in the 

 vertebrates, particularly in the mammals and the 



b66] 



