viii PREFACE 
for the editor to write short chapters on certain topics that were not 
presented in the available literature in sufficiently brief compass or 
in sufficiently non-technical language. 
The one-man textbook is only too often written to emphasize 
the author’s pet theories and is likely to be unduly biased. The 
present work is completely non-partisan. It consists of the writ- 
ings of many authors and presents many diverse theories. The 
student is left to balance the various views one against another and 
to form his own judgment. 
It is very unfortunate, but none the less true, that even in these 
scientific days, the subject of evolution has a bad name in many 
communities, and in many educational institutions with religious 
affiliations. The, mistake is made of supposing that evolution and 
religion are diametrically opposed. The present writer has been at 
some pains to make it clear that evolution and religion are strictly 
compatible. We teachers of evolution in the colleges have no sinister 
designs upon the religious faith of our students. 
While this book is intended primarily for a college textbook, 
we have also had in mind the general reader. Apart from a few of 
the more technical details, the text seems to us very readable. The 
language of the great classic writers—Darwin, Wallace, Romanes, De 
Vries, Le Conte—is simple and lucid. Among recent biological books 
few are written so freshly and vividly as those of Professor J. Arthur 
Thomson. The clearness and scientific accuracy of Conklin, Saleeby, 
Guyer, Walter, Lull, Osborn, the Coulters, Downing, Shull, Tayler, 
Popenoe, Johnson, and others, are familiar to American biologists. 
Scrupulous care has been taken to verify all passages quoted, 
but it is hardly likely that, in so large a mass of material, all errors 
shall have been avoided. The author and the publishers would 
welcome as a favor any suggestions or corrections submitted by 
interested readers. 
A list of fifty books from which material has been quoted is given 
on pages 510-512. To the authors and publishers of these books and 
monographs we wish herewith to tender our grateful acknowledg- 
ments for their generosity and co-operation. A considerable amount 
of material for which permission to reprint had been granted fails 
to appear in the present volume. It is hoped to incorporate this 
material in an appendix to a later edition, or else to use it in the form 
of a small volume of supplementary readings. 
H. H. N. 
August 15, 1921 
