ADJUSTMENT, DIRECT AND INDIRECT 



i Equilibration 



p. . r Direct Adaptation. 



X erna < indirect Natural Selection, 



P , \ I Correlation of Growth. 



(^ Indirect Use and Disuse, 



Here we have a classification of agencies co- 

 extensive with our present knowledge of the 

 subject, and sufficiently comprehensive to in- 

 clude such factors in the problem as may here- 

 after be discovered. Under one of these four 

 subdivisions every special process concerned in 

 forwarding organic evolution must be included. 

 For since it is admitted on all sides that specific 

 change is due to the necessity for maintaining 

 equilibrium between the organism and the en- 

 vironment, it follows that every process which 

 results in the modification of species must be a 

 process of adjustment or equilibration, either 

 external or internal, direct or indirect. In the 

 scientific treatment of the problem, there is 

 room for much beside natural selection, but 

 there is no room for occulta vires, or pantheis- 

 tic intelligences, or for " tendencies," save such 

 as may be expressed as the unneutralized sur- 

 plus of forces acting in a particular direction. 



But we have now done something more than 

 merely to classify the causes of organic evolu- 

 tion. In the act of classifying these, we have 

 arrived at the law or formula which expresses 

 the chief characteristic of organic evolution. 



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