LEE BARKER WALTON 119 



IV. A Working Hypothesis of Evolution 



Investigations during the last fifteen years, instead of 

 establishing evolution as the simple process of natural 

 selection conjectured by Darwin and others, have made it 

 evident that the results are due to many factors of much 

 complexity. While the diversity of organisms depends 

 on variation — their inheritance and non-inheritance — it 

 is becoming more and more apparent that the term is too 

 comprehensive and covers variations arising in organisms 

 from causes quite different from one another. 



The results reached in the preceding pages indicate the 

 need of extending the older terminology as used by Plate, 

 '13, and others where variations are separated into 

 "somations" or fluctuations induced by the environment 

 and not inherited, and "mutations" or blastovariations 

 arising in the germ plasm and inherited, if a clearer 

 understanding is to be obtained of evolution and its ap- 

 plication. Therefore the following scheme is proposed.^ 



Variations 



A^. Apparently originating in accordance with 



definite laws A. NORMATIONS. 



B^. Induced by general environmental stimuli, 

 (food supply, use and disuse, etc.), but not 

 inherited so far as evidence shows 1. Fliictnations. 



B'^. Not induced by environmental stimuli; in- 

 herited. 



C^. Arising throvigh the transference of 

 factors by the combination of two ancestral 

 lines in accordance with Mendelian prin- 

 ciples, but exhibiting "per se" no definite 



progress 2. Amphinmtations 



("mutations" in part). 



C^. Arising through causes at present un- 

 known, but which, from the progressive re- 

 sults obtained, may be assumed to originate 

 in accordance with definite laws 3. Cumtilationsr 



Several interesting groupings of variations have been suggested by Spillman, 

 Baur and others, none of which, however, appear to meet present conditions. 



"Cumulations — from cumulo, to increase — including the names of the following 

 groups, with the exception of fractionations proposed by Bateson, are based on the 

 apparent origin of the variations. 



