PROCEEDINGS 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VIII, pp. 197-403. February 13, 1907. 



ASPECTS OF KINETIC EVOLUTION. 

 By O. F. Cook. 



The kinetic theory of evolution finds in the facts of organic 

 development indications that the characters of species change 

 spontaneously, or without environmental causation. Evolution- 

 ary progress is further conceived as accomplished through the 

 union of the normally diverse individual members of species into 

 a coherent network of interbreeding lines of descent, rather than 

 by the isolation of variant individuals or by the selective restric- 

 tion of descent to individuals possessing particular characters. 



Former theories have undertaken to explain the method of 

 evolution by reference to the dendritic figure of descent as shown 

 in the ever-branching relationships of species, genera and fami- 

 lies. The kinetic interpretation of the evolutionary process is 

 based on what may be called the intraspecific figure of descent, 

 the relationship of organisms inside the species, which is reticu- 

 lar or net-like, and not tree-like. 



Theories based on the dendritic conception of descent may 

 also be described as differential ; that is, they have given atten- 

 tion chiefly to the problems of distinction and separation of 

 organic groups. The kinetic theory is integral or synthetic, 

 and conceives the evolutionary process as conducted by the 

 accumulation and combination of the variations which appear 

 among the members of the species. 



These simple distinctions are fundamental, and will neces- 

 sitate an extensive readjustment of methods of thought and 

 investigation in the field of evolution. 



