ASPECTS OF KINETIC EVOLUTION 323 



nating the unfit. The problem, as to how the individual steps 

 are brought about, is quite another side of the question." 1 



This is in notable contrast with the previously quoted dictum 

 of Professor Lankester, regarding an " ever-watchful natural 

 selection " by which characters are " seized upon " and " raised 

 to a high pitch of growth and function." 



INTERBREEDING AS AN EVOLUTIONARY FACTOR. 



In full accord with the idea that evolutionary change or motion 

 is caused by selection or environmental influence, are the opin- 

 ions, already emphasized, that isolation is necessary to preserve 

 new characters, and that the sexual phenomena of interbreeding 

 stand in the way of evolutionary progress by hindering the per- 

 petuation of new characters. These corollaries of the selection 

 hypothesis find no place in the kinetic theory. Interbreed- 

 ing and other phenomena of sexuality have been reckoned 

 in the present discussion as positive factors in evolutionary 

 motion. 



Evolution, in the kinetic interpretation, represents the work- 

 ings of no special force, principle or mechanism ; it is carried 

 forward by the symbasic interbreeding of the diverse individuals 

 of which species are composed. The final and ultimate expla- 

 nation of evolution must await an understanding of the constitu- 

 tion of living matter. We must learn why the prepotent genetic 

 variations occur, and why the interbreeding is necessary. But 

 having once appreciated the variations and the interbreeding as 

 ever-present facts, evolution is no longer mysterious ; it follows 

 as a natural and obvious consequence. 



THE KINETIC FIGURE OF EVOLUNTIONARY MOTION. 



It will be apparent from the preceding chapters that the evo- 

 lutionary motion predicated under the kinetic theory differs 

 from that of previous doctrines in important respects. In the 

 first place, it is a highly complex or compound motion instead 

 of a simple one, not to be typified by a push from the environ- 

 ment, by a pull by natural selection, by an occasional mutative 

 leap, nor even by the onward transportation of a determining 



"DeVries, H., 1905. Species and Varieties, p. 6. 



