322 O. F. COOK 



The more specialized groups abound in characters which in- 

 stead of being explainable as called forth by natural selection, 

 and hence as useful, appear to have been pushed to worse than 

 useless extremes. It is as though species were impelled from 

 within by an essential kinesis or property of motion to make 

 trial of every feasible degree of expression of every attainable 

 character. Kinesis is not a mysterious force or mechanism to 

 be sought in reproductive cells ; it is a general property of or- 

 ganisms, as gravitation is of matter. And of kinesis we know 

 more than of gravitation. Two factors and two results are al- 

 ready obvious. The factors are heterism, or intraspecific diver- 

 sity, and symbasis, or interbreeding in a specific network of 

 descent. The results are the sustained variety of the inter- 

 breeding organisms, and the continuous progressive modifica- 

 tion of the specific groups. 



The normal evolutionary progress or vital motion of organ- 

 isms is symbasic ; they advance in large groups of interbreed- 

 ing individuals, commonly called species. Separate mechanical 

 explanations of each example of this law are as superfluous as 

 the mediaeval angels who pushed the planets round and hurled 

 the meteors. Nobody doubted that the meteors and planets 

 moved, but special causes continued to be conjectured until it 

 was discovered that the earth itself was also in motion. If 

 species were normally stationary, the environment must needs 

 have impelled them. They have, however, motions of their own. 



Natural selection neither originates species nor actuates their 

 further development ; progressive change would go on whether 

 selection were active or not, and whether the environment were 

 uniform or not. Nevertheless, selection conduces to adapta- 

 tion, since by permitting changes in some directions and for- 

 bidding them in others, it deflects the specific motion. The 

 workings of natural selection are adequately explained only 

 under the kinetic theory, which recognizes the physiological 

 value of organic changes as such, and which thus supplies the 

 materials on which selection can act.' 



The organic structure is held together and supported by the 

 symbasic interweaving of different lines of descent. When the 



'Natural Selection in Kinetic Evolution, Science, N. S., 19: 594. 



