Modern evolutionary theory is the great unifying concept of biology. 

 It represents the major theoretical triumph of the biological sci- 

 ences-an all-embracing theory which attempts to explain the mani- 

 fold complexities of biological phenomena. The biochemist attempt- 

 ing to understand the genetic code, the neurophysiologist probing 

 the complex mechanisms of the mind, the embryologist seeking to 

 understand how one tissue affects the development of another^ in- 

 deed, all biologists, are working on problems whose theoretical sig- 

 nificance can be measured only by their contribution to our under- 

 standing of evolutionary phenomena. The biochemist may be able 

 eventually to cure cancer, the neurophysiologist to vmderstand 

 mental disorders, and the embryologist to discover how the genetic 

 code is translated into an organism. But, without a theory that inter- 

 relates all these phenomena, their work would have onlv applied 

 significance. 



The central position of evolution in biology has long been recog- 

 nized. Nevertheless, most laymen and many biologists are largely 

 ignorant of modern evolutionary theory. This book is an attempt to 

 supply a reasonably concise volume dealing with organic evolution. 

 It has been written for the reader concerned more with the process 

 of evolution than with its products per se. There are no pictures of 

 dinosaurs, no taxonomic descriptions of organic diversity, and no 

 discourses on the history of evolutionary thought. 



We have assumed that our readers have reached at least that le\el 

 of biological sophistication attained in a rigorous university course 

 in biology. We hope that the book will serve as a challenging text 

 for an undergraduate course in e\'olutionary theory, as a basic text 

 to be supplemented with outside reading for a graduate course, 

 and as general reading for biologists in other fields who may wish 

 a brief review of what is known of the process of evolution. Most of 

 the material presented has been used in either the undergraduate 

 course in evolutionary processes or the course in advanced topics in 

 evolution at Stanford University. 



An attempt has been made to present evolutionary theory as a 

 unified whole. Because we are assuming some familiarity, at least 

 on a casual level, with phenomena such as selection and mitosis, wo 

 have felt free to make passing reference to them before they are 

 treated in detail. Life, meiosis, genetic systems, culture, and the 

 like have not been taken for granted. Rather we have attempted to 

 show how these phenomena are themselves the result of evolu- 

 tionary processes. Necessarily this involves speculation, which \m- 



VII 



