PREFACE vii 



Hewitt Lectures because the writer holds the deeply 

 grounded conviction that evolution has been continuous 

 throughout, and that the study of lower organic forms 

 where laws reveal themselves in more fundamental 

 simplicity must lead the investigator to employ and 

 apply those laws in the study of the highest natural 

 phenomena that can be found. Another motive was 

 equally strong. Too frequently m.en of science are 

 accused of restricting the apphcation of their results to 

 their own particular fields of inquiry. As individuals 

 they use their knowledge for the development of world 

 conceptions, which they are usually reluctant to dis- 

 play before the world. It is because I beheve that 

 the accusation is often only too well merited that I 

 have endeavored to show as well as circumstances 

 permit how universal is the scope of the doctrine based 

 upon the facts of biology, and how supreme are its 

 practical and dynamic values. 



It remains only to state that the present volume 

 contains nothing new, either in fact or in principle; 

 the particular form and mode of presenting the evolu- 

 tionary history of nature may be considered as the 

 author's personal contribution to the subject. Nothing 

 has been stated that has not the sanction of high author- 

 ity as well as of the writer's own conviction ; but it 

 will be clear that the believers in the truth of the analysis 

 as made in the later chapters may become progressively 

 fewer, as the various aspects of human life and of human 

 nature are severally treated. Nevertheless, I believe 

 that this volume presents a consistent reasonable view 

 that will not be essentially different from the con- 

 ceptions of all men of science who beheve in evolution. 



