ASPECTS OF KINETIC EVOLUTION 303 



theory of Darwin in holding evolution to be independent of 

 natural selection. It reverses the panmixia doctrine of Pro- 

 fessor Weismann, in that it treats the interbreeding of the 

 numerous and diverse individuals of species as conducive of 

 biological motion, instead of as hindering it. It is the reverse 

 of the mutation theory of Professor De Vries, in that evolu- 

 tion is held to go forward normally in entire species, and not 

 merely in individuals or in narrow lines of descent. 



One of the chief weaknesses of all the static doctrines, both 

 saltatory and selective, lay in the apparent necessity that new 

 variations be isolated from their relatives in order to preserve 

 their new characters and make evolutionary advance possible, 

 for the fundamental concepts of the static doctrine are the 

 normally stationary average and the swamping effects of inter- 

 crossing. 



The kinetic theory differs fundamentally from all its prede- 

 cessors in recognizing the fact that evolution is not a process of 

 segregation, but of synthesis and integration. The transforma- 

 tion of species in nature is brought about by the sharing of in- 

 dividual variations through interbreeding. Conjugation and 

 cross-fertilization do not hinder evolution, but are essential to 

 the gradual building up of the intricate coordinations of char- 

 acters through which adaptations and other desirable changes 

 go forward. Selection, inbreeding, isolation and other forms of 

 segregation, reduce the number of accessible variations, narrow 

 the basis of the vital structure, and result in organic weakness, 

 sterility and extinction. Selective isolation accentuates par- 

 ticular variations and has been utilized in the diversification of 

 domestic varieties of plants and animals useful to man, but 

 abnormal and weak from the evolutionary standpoint, and 

 affording no complete analogy with the natural development of 

 organic types. The sterility of many hybrids and the tendency 

 of inbred varieties to produce relatively infertile sports may 

 prove to be explainable by the same fact of inadequate fertili- 

 zation. For want of better words it may be said that the vital 

 tension of inbreeding is too little, while that of hybridity is too 

 great; the normal course of biological evolution lies, obviously, 

 between the two extremes. Evolution, or biological motion, 



