ASPECTS OF KINETIC EVOLUTION 2 I 5 



tion of desert animals is a very complex phenomenon, not to be 

 explained merely by coincidence, nor by environmental reac- 

 tion, nor even by the selection of reactions. 



The possibility of developing such elaborate contrivances is 

 not adequately conceived until we are able to think of the species 

 as having an active instead of a merely passive evolution, until 

 we recognize that species have internal as well as external 

 reasons for continuing to put forth variations of all the charac- 

 ters they possess, as long as the environment does not forbid. 

 The endless possibilities of adjustment can then be realized, for 

 the narrower the environmental road the more definitely adap- 

 tive must be the evolutionary motion of the species. 



ORGANIC UTILITY AND ENVIRONMENTAL FORTUITY. 



The utility of new characters is not to be narrowly restricted 

 to the environmental sense. New characters can be thought of 

 as having what may well be termed an organic utility, quite 

 apart from their effects upon environmental relations. They 

 may afford a desirable stimulation like that commonly shown in 

 the greater vigor of crosses between organisms not too unlike, 

 and they may also contribute to the structural perfection and 

 general efficiency of the organism. Both these effects of new 

 characters would give the new type environmental and selec- 

 tional advantages, but indirectly, and not to the exclusion of 

 other more definitely adaptive contributions to constructive 

 evolution. 



In the recognition of physiological values for new characters 

 the kinetic theory of evolution diverges widely from the older 

 doctrine that species are normally constant and stationary until 

 changes are brought about by environmental influences. Al- 

 though often misnamed dynamic, this conception was in reality 

 static, for the organisms were supposed to have no power of 

 change except as worked upon by the external causes. Never- 

 theless, variations, even when ascribed to the environment, were 

 often held to be merely fortuitous in their relations to evolution, 

 for it was not believed that they would be preserved and accen- 

 tuated except by natural selection. The development of useless 

 characters could not be admitted under this theory, although it 

 Proc. Wash. Acad. Sci., December, 1906. 



