302 COOK 



each of these types of evolutionary theories may be said to rest 

 upon certain groups of evolutionary facts which are more or less 

 completely ignored by the others. The niceties of many adapta- 

 tions to environment have led Darwin and his followers to 

 almost exclusive reliance upon that factor. Saltatory theories 

 provide larger variations, but require even more effective isola- 

 tion. Determinant theories deny the influence of environment 

 and must ascribe adaptations to accident or to pre-established 

 harmony. All three theories antagonize the obvious fact that 

 a very general tendency of organic development has been 

 toward the increase of facilities for cross-fertilization. These 

 have been interpreted as inimical to evolution because they 

 interfere with the preservation of the abnormally close-bred 

 variations which have been mistaken for true steps in the 

 progress of organic series. 



KINETIC OR SYMBASIC EVOLUTION. 



Somewhat between the doctrines of selection and of deter- 

 mination, but distinct from both, is another conception of evolu- 

 tionary motion, that it is caused neither by external environments 

 nor by internal mechanisms, but goes forward as a necessary 

 result of the normal specific constitution of living matter. It is 

 observed that organisms normally exist and make evolutionary 

 progress only in large groups of interbreeding individuals. 

 Evolution is, in a word, symbasic ; that is, organisms must 

 travel together along the evolutionary pathway, and must be 

 connected with each other by an intricate network of descent 

 in the weaving of which the diversities of the members of a 

 species have a definite physiological value. Without diversity 

 of descent the cellular organization deteriorates. This being 

 the case, it is easy to understand that new variations are pre- 

 potent, and that species make more rapid evolutionary progress 

 in proportion to their numerical size. The larger and more 

 widely distributed the species, the greater the opportunities of 

 variation and of evolutionary progress. 



Kinetic evolution is thus the reverse of many current theories, 

 in that it recognizes a normal and necessary movement of change 

 not caused by environment. It is the reverse of the selective 



