ADAPTATION VERSUS INHERITANCE. 253 



animal and vegetable forms, which, in fact, they have. We 

 have, at least, hitherto been unable to discover any other 

 formative causes besides these two, and if we rightly under- 

 stand the necessary and infinitely complicated interaction 

 of Inheritance and Adaptation, we do not require to look 

 for other unknown causes for the change of organic forms. 

 These two fundamental causes are, as far as we can see, 

 completely sufficient. 



Even long before Darwin had published his Theory of 

 Selection, some naturalists, and especially Goethe, had as- 

 sumed the interaction of two distinct formative tendencies 

 — a conservative or preserving, and a progressive or chang- 

 ing formative tendency — as the causes of the variety of 

 organic forms. The former was called by Goethe the cen- 

 tripetal or specifying tendency, the latter the centrifugal 

 tendency, or the tendency to metamorphosis (p. 89). These 

 two tendencies completely correspond with the two processes 

 of Inheritance and Adaptation. Inheritance is the centri- 

 petal or internal formative tendency which strives to keep 

 the organic form in its species, to form the descendants like 

 the parents, and always to produce identical things from 

 generation to generation. Adaptation^ on the other hand, 

 which counteracts inheritance, is the centrifugal or external 

 formative tendency, which constantly strives to change the 

 organic forms through the influence of the vaiying agencies 

 of the outer world, to create new forms out of those existing, 

 and entirely to destroy the constancy or permanency of 

 species. Accordingly as Inheritance or Adaptation pre- 

 dominates in the struggle, the specific form either remains 

 constant or changes into a new species. The degree of con- 

 stancy of form in the different species of animals and 



