ASPECTS OF KINETIC EVOLUTION 223 



rigorous with regard to some particular faculty or feature, but 

 generally allowing wide liberty of chance and choice in other 

 respects. The adaptations are seldom so close that no further 

 beneficial or indifferent changes can be made. If we attempt, 

 by artificial selection, to enforce too narrow restrictions and main- 

 tain a closely uniform type, the effort always fails through the 

 deterioration of the organism. The total fitness of species to 

 their environments is simply the summary of their past histories. 

 It has nothing in particular to do with evolutionary causes. 1 

 The problem of fitness appears to be truly insoluble under the 

 idea of normally stationary species. The postulates of the older 

 selective doctrine are in direct logical agreement with each other, 

 but one without the other is completely inoperative as a working 

 hypothesis. Some have even denied adaptation because they 

 despaired of explaining it, but all these difficulties disappear 

 when the point of view is changed. Kinetic evolution supplies 

 more abundant materials on which selection can act, and explains 

 how fitness can come about without environmental causation. 

 We are not obliged to discredit the evidence of our senses that 

 adaptations exist, nor to reject the obvious probability that they 

 are induced, though not caused, by the environment itself. All 

 the difficulties are surmounted when we appreciate the fact that 

 the environment works by the restriction and deflection of a 

 normal evolutionary motion, and not as a direct or actuating 

 cause. The environment furnishes certain specifications regard- 

 ing what may be built, but builds nothing itself. Changes of 

 the environments imply changes of the vital specifications ; they 

 enable new evolutionary steps to be taken, but the species itself 

 must originate and develop the appropriate variations before 

 selection can favor them with its discriminating encouragement. 

 The strength of the theory called Darwinism, that evolution 

 is caused by natural selection, lay largely in the fact that it 

 presented a solution of the problem of fitness, and could then 

 explain evolution through adaptation. Darwinism was rational 



'The word environment is itself the occasion of great ambiguity in evolu- 

 tionary literature, some writers using it with reference to its supposed power 

 to cause favorable variations, and others merely as a summary of selective influ- 

 ences. Between these two extremes there are many gradations of emphasis, so 

 that two writers may use the same words in expressing contradictory opinions. 



