PREFACE TO THE SECOND EDITION xi 



have contributed directly to the immediate preparation of the volume. First 

 among these I must mention Dr. Louise F. Bush, whose creative and in- 

 terpretive drawings have added so much to the teaching value, as well as to 

 the appearance, of the book. Most of the illustrations not borrowed un- 

 changed from other sources are her work. I am also grateful to my col- 

 league, Lyman S. Rowell, for two most useful drawings, to Dr. H. B. D. 

 Kettlewell for two beautiful photographs of industrial melanism, and to 

 L. W. Erbe for a photograph upon which the drawing of a tapir was based. 

 Publishers and authors have been most generous in permitting me to bor- 

 row illustrations; for this 1 am grateful. The caption of each borrowed fig- 

 ure credits the source of the figure. 



My indebtedness continues to many individuals who contributed in 

 various ways to the first edition. Space Umitations prevent mention of many 

 of those to whom I am indebted, but because of the magnitude of their 

 contributions it is a pleasure to recall the help ofl'ered by Joseph G. Baier, 

 David W. Bishop, Charles F. Bond, Theodosius Dobzhansky, John T. 

 Emlen, William K. Gregory, David Lack, John H. Lochhead, Ernst Mayr, 

 Mabel L. Moody, Marjorie S. Murray, Carl T. Parsons, Henry F. Perkins, 

 George Gaylord Simpson, and a geologist whose name was not divulged to 

 me. It would also be a pleasure to list the names of those who, orally or in 

 writing, have suggested changes for the second edition. James M. Barrett, 

 Ross T. Bell, and Bobb Schaeffer are typical of many whom I should like 

 to mention. While the persons listed have contributed greatly to whatever 

 merits the book may possess, they are entirely without responsibility for 

 its deficiencies. 



It is my hope that readers of this edition will be as cooperative in sending 

 me their constructive criticisms as were readers of the first edition. 



An Explanatory Note for Students 



The illustrations are numbered according to the system of including the 

 number of the chapter in the number assigned the illustration. Thus, "Fig. 

 4.10" indicates that the figure in question is the tenth one in Chapter 4. 

 The next illustration in that chapter is numbered "Fig. 4.11," and so on. 



In most places the name of a contributor to evolutionary thought is fol- 

 lowed by a date, usually in parenthesis — e.g., "Darwin (1859)." The date 

 enables one to identify the publication referred to, listed with the author's 

 name at the end of the chapter. 



Paul A. Moody 

 Burlington, Vermont 

 December, 1961 



