



PREFACE TO THIRD EDITION 



The first edition of this book was avowedly a book of readings, a 

 source book, consisting almost exclusively of extracts from leading 

 writers on evolutionary topics. The character of the book made it 

 somewhat disjointed. It was criticized for lack of unity of plan and 

 was called by one critic a hodge-podge. In spite of these defects many 

 teachers found the book valuable as a reading source to accompany 

 lectures. 



In the second edition an attempt was made to unify the material 

 by the addition of a considerable amount of editorial comment in the 

 form of short introductory and transitional chapters. This method of 

 unification was, however, not sufficiently radical. The result was nei- 

 ther a source book nor an organized textbook. Believing that what 

 most teachers want is primarily a textbook and only secondarily a 

 source book, the author has attempted to make the book a text by 

 reorganizing the previously less organized material and by taking out 

 and putting into the Appendix chapters that break the continuity of 

 treatment but are useful for collateral reading. 



Teachers using the book recommended that the historical account of 

 evolution and the section on evidences of evolution be left substantially 

 as they were, but they suggested that the section on genetics be largely 

 rewritten. This has been done. The plan followed is that of dealing 

 with genetics as the study of the mechanism of evolution, the main 

 factors of which are (i) the persistence factor, heredity; (2) the diver- 

 sity factor, sexual reproduction and Mendelian heredity; (3) the change 

 factor, mutation; (4) guiding factors, selection, and possibly the 

 Lamarckian factor and orthogenesis; and (5) the dividing factor, isola- 

 tion in the broad sense. The part on eugenics has also been extensively 

 revised and rewritten, and contains a good deal more factual material. 

 It is hoped that in its present form the book may more nearly meet the 

 needs of college classes in evolutionary biology. 



It gives us pleasure to acknowledge gratefully the permission given 

 us by The Macmillan Company to use figures 40, 41, 42, 43, 44, 45, 

 and 51. 



H. H. Newman 

 University of Chicago 

 January 16, 1932 



