PREFACE 



This book has been prepared to meet a specific demand, long 

 felt here and elsewhere, for an account of the various phases of evolu- 

 tionary biology condensed within the scope of one volume of moderate 

 size. The present writer has now for sixteen successive years pre- 

 sented in lecture form to large classes of students the subjects of 

 evolution, genetics, and eugenics. Never have we been able to find 

 a single book that would cover the required ground. In fact it has 

 been necessary to require, or at least to recommend, as many as 

 three books. It is beUeved that the present book will furnish ade- 

 quate reading material for a major or a semester course in evolutionary 

 biology. Some supplementary reading may be necessary in case an 

 instructor wishes to emphasize one or more phases of the subject; 

 but for a first course in the subject we believe that all of the essential 

 reading material will be found within the text itself. 



An effort has been made to present the subject in the best peda- 

 gogical order. After a general introduction, a rather long chapter 

 appears in which the whole history of the development of evolution- 

 ary science is outlined, together with the names and contributions 

 of the leading evolutionists. Part II is a presentation of the evi- 

 dences of organic evolution, beginning with the bodies of e\ddence 

 most definite and direct, and ending with the less definite and 

 more controversial. Part III deals with causo-mechanical theories of 

 evolution with Darwinism as the central topic. Part IV concerns 

 itself with genetics or modern experimental evolution, and Part V 

 with eugenics, or genetics as applied to human improvement. 



The book consists largely of excerpts, some long and some short, 

 from both the older classical evolutionar>' writers and the modem 

 writers. Our aim has been to select the most significant or character- 

 istic passages from each author. In most cases this ideal has been 

 attained, but it has sometimes happened that we have had to make 

 our selection of material to meet a real need in the book, and accord- 

 ingly have selected from an author a passage he himself might not 

 consider particularly characteristic of his work. We have succeeded, 

 nevertheless, in welding together out of a collection of isolated chapters 

 and passages what seems to us to be a close approach to a coherent 

 unit. Unification has been accomplished by the aid of editorial 

 connecting passages, introductory statements, criticisms, and sum- 

 maries. In certain cases it became necessar}^, for a variety of reasons, 



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