IV Preface 



specific qualities and attributes, and with these and the old to create an array 

 of new types, new genera, or even of higher taxonomic groups of organisms, 

 and with this as a basis it is possible to attempt the third part of the project. 



This last part involves experimenting in nature with new forms to discover 

 how newly arisen characters, or their combination into specific forms, behave as 

 they meet the conditions of the environment into which they are thrust by the 

 processes of their origination. It is in this way only that it may be possible to 

 discover methods of elimination, of preservation, of adaptation, and the study 

 of kindred problems, that are of vital import in the total evolutionary activities 

 in nature, and which are now the delight of the essayist. 



Throughout this work " factor " and " determiner " are used in a physical 

 and dynamic sense, and are nowhere used in the sense of a carrier, representa- 

 tive or otherwise, of anything pertaining to the characters of organisms. The 

 word " factor," an agent that makes possible a general result, has been too often 

 used by some Neo-Mendelians in the sense of a carrier, but I am not able to dis- 

 cover that this use (in the Weismannian sense) is justified, and investigations 

 of the Mendelian reaction do justify the use of the term in the physical sense 

 in which I have used it. A " determiner," on the other hand, is an agent which 

 by its interaction with a factor decides which one out of several possible results 

 shall ensue. 



The presence of reactions involving these gametic agents in diverse aspects 

 of the same materials, the experiments showing that the factors are specific in 

 reaction only when present in a specific system and environment, are the reasons 

 for the attempt to formulate these results in a general hypothesis of evolutionary 

 action and causation. Unlike other evolution hypotheses any dynamic con- 

 ception must be heterogeneous in action and result, a complex of many factors 

 and types of reaction and nowhere due to the operation of a single agency. I 

 have found in my materials that transmutation may be by sudden changes, by 

 slow accumulation, by hybrid reaction, and by means of environmental forces, 

 and in all changes the basal operations involved are purely physical types of 

 reaction between the gametic agents and the condition surrounding the reaction. 



I have been fortunate in the support that this project has been given. Soon 

 after the start it was given added impetus through aid from the Elizabeth 

 Thompson Science Fund; later the Carnegie Institution of Washington gave 

 sundry grants for some of the investigations in the tropics, and in the later 

 years larger and continued support at the Desert Laboratory in Tucson, Arizona, 

 and at the Laboratory of Marine Biology at Tortugas, Florida. Also the Uni- 

 versity of Chicago has liberally supported the project, and especially the experi- 

 mental portions of the investigation requiring controlled and exact conditions. 

 I am deeply indebted to President H. P. Judson for most cordial support in 

 the project, and to the late Professor C. 0. Whitman, and especially to my 

 colleague. Professor F. R. Lillie, for many kind acts and aid which in divers 

 ways have contributed to the forwarding of the investigation. To President 

 R. S. Woodward, of the Carnegie Institution of Washington, and Dr. D. T. 

 MacDougal, Director of the Desert Laboratory at Tucson, Arizona, is due the 

 credit for an opportunity to conduct upon an unusually extensive scale and, 

 under favorable conditions, a series of experimental studies in the Arizona 

 deserts. The creation of an elaborate plant with trained assistants has given 

 me the best opportunity to experiment direct in nature. 



