INTRODUCTION 8 



most ways it is not novel; most of the ideas con- 

 tained in it have been expressed in some form else- 

 where. But novelty is not the only valid reason 

 for writing. The reason for this work is a sincere 

 belief that it approaches fundamental problems 

 of evolution without prejudice, that it paves the 

 way for a rational examination of details, and that 

 it furnishes a rational basis for experimentation 

 which has hitherto been obscured by mistaken 

 attitudes. 



At the outset a word should be said of the possi- 

 ble fields of inquiry in evolution, for it is possible 

 to find unnecessary prejudice even in methods of 

 approach. One writer ^ summarily dismisses the 

 results of philosophical inquiry when conducted 

 without close association with laboratory investi- 

 gation. To the extent that an inquiry may be 

 purely philosophical I heartily agree with his atti- 

 tude, but it suggests to me that there are two dis- 

 tinct courses to be followed in phylogenetic studies. 

 We may, on the one hand, confine ourselves to the 

 examination of various lines of descent, determin- 

 ing the spatial and chronological relationships of 

 the various included species and the environmental 

 conditions under which they arose, and construct 

 phylogenetic trees of great practical value and 

 interest in the field of science. On the other hand, 

 we may interest ourselves in the broader aspects 



2 Sewertzoff, A. N., Acta Zoologica, Vol. X, pp. 59-141. 1929, 



