STAGES OF VITAL MOTION. 15 



from their unimproved relatives. Variation is not a consequence of 

 adaptation; adaptation is a result of variation.* 



Heredity and variation are not two opposing forces, the one tend- 

 ing to preserve and the other to destroy the specific type; they are 

 two closely adjacent aspects of the single process of organic succession. 

 The permanence of types is not secured by stable or unchanging char- 

 acters, but by individual diversity or inconstancy, and the consequent 

 power to move in advantageous directions. Organisms are so consti- 

 tuted that the persistent repetition of the same form or character com- 

 plex is not possible; the supposition of a non-progressive heredity 

 comes from the pre-evolutionary period. Heredity does not oppose 

 variation ; evolution is the inheritance of variations, facilitated by cross- 

 fertilization. The causes of variations are also the causes of the ac- 

 cumulation of variations, and of the resulting diversity of species. 

 Variation and cross-fertilization are the means, while selection and 

 isolation are the incidents, of a continuous organic motion. Species 

 are not normally at rest, nor are their motions predetermined by ex- 

 ternal forces or by internal mechanisms; they are not compelled in 

 one direction, but must move in some direction, as variation and en- 

 vironment permit. 



The Accumulation of Variations. 



Static theories are further inadequate because they neglect the fact 

 that change or biological motion is necessary to maintain the vigor and 

 eflSciency of the organism. A kinetic theory,t on the other hand, 

 recognizes such motion as normal, and as facilitated by cross-breeding, 

 instead of being hindered. In whatever environment and however 

 propagated, organisms of all types and all categories of complexity are 

 changing or evolving, though with unequal rapidity. Organisms mul- 

 tiplied asexually and thus connected only in simple or linear series 

 make slow progress in comparison with groups in which variations can 

 be distributed through cross-fertilization. The more complex the or- 

 ganic structure the greater the necessity that it be supported, as it 

 were, by many diverse, intergrafting lines of descent. The reasons for 

 this have not been explained, but for purposes of expression it may be 

 ascribed to a special property or requirement called symbasis,| served at 



* Reactions to environment are often termed ' adaptations,' but the word 

 in this sense is without evolutionary significance because it has not been shown 

 that any non-congenital variation is hereditary. 



t'A Kinetic Theory of Evolution,' Science, N. S., XIII., 969, June 21, 

 1901; 'Kinetic Evolution in Man,' Science, N. S., XV., 927, June 13, 1902. 



J Symbasis signifies etymologically a moving or standing with or together. 

 The similarity of the word to symbiosis is perhaps objectionable, but may assist 

 in the appreciation of the distinction between static and kinetic views. Sym- 

 biosis means the living together of different species of organisms on terms of 



