ASPECTS OF KINETIC EVOLUTION 225 



The kinetic theory rejects the hypothesis of environmental 

 causation of evolution as fatally discordant with the facts of 

 organic nature. The individual members of species are normally 

 diverse, even under the same conditions ; the fact that they may 

 differ under different conditions is not to be accepted as a proof 

 of environmental causation of evolution. 



There are two phenomena of organic fitness : first the adap- 

 tation to environment afforded by the general characters of the 

 species ; and second, the power often shown by individual 

 plants and animals to adjust themselves to varied environmental 

 conditions. The latter is a form of organic elasticity compara- 

 ble, in a general evolutionary sense, to muscular contraction 

 and locomotion, and with no special significance as a factor of 

 evolution, nor any special pertinence as an example of the 

 method of evolution. 



Both kinds of fitness are results of evolution, instead of being 

 causes. They are fruits of the tree, not the roots. Fitness is 

 maintained because evolution continues, not because the environ- 

 ment works changes in organisms. For the static evolutionist, 

 fitness becomes an abstract and insoluble problem. Viewed 

 from the kinetic standpoint, it appears as a natural and neces- 

 sary consequence of a spontaneous evolutionary motion con- 

 trolled or deflected by selective influence. 



Environments continually change, and with them the relative 

 utility of characters. A feature useless in one environment may 

 be of value in another, or a useful character may become use- 

 less or even detrimental, depending on external circumstances. 



There is thus a real and intimate relation between fitness and 

 environment, but not a relation which can justify recourse either 

 to natural selection or to direct adaptation, as causes of evolu- 

 tion. It is not to be taken for granted that all the differences 

 shown by plants or animals when environments are changed are 

 in the direction of fitness. With different conditions and mate- 

 rials, organisms build differently, or they may wander from the 

 pathway of normal development in unwonted surroundings. 

 Natural selection encourages fitness by preserving the fittest, 

 but there are also environmental differences with no adaptive 

 relation, and upon which selection exerts no influence. 



