CHAPTER XXI 



Resume 



The present status of the question. — Differentiation and adapta- 

 tion. — Theories of differentiation: mutation, orthogenesis, 

 isolation. — Theories of adaptation: Darwinism and Lamarck- 

 ism. — Natural selection, transmission of acquired charac- 

 ters. — The limits of adaptation. — Structure and function. — 

 Non-adaptive variations. — Increasing complexity of living 

 things. — A possible solution of the question at issue. 



THE questions we have examined in the course 

 of the foregoing chapters are many and varied, 

 the theories reviewed are very different and some- 

 times irreconcilable; by surveying rapidly the field 

 just covered, we will be able to derive a clear idea of 

 the problems now wanting solution. 



Two important phenomena mark the evolution of 

 the organic world ; one is the appearance ofthe^iff er- 

 ent species, the differentiation of the various groups 

 recognised in the usual classification of animals and 

 plants, the increasing complexity of organisms, their 

 evolution from the lowest to the highest forms; the 

 other is the adaptation of living things to the condi- 

 tions and necessities of their environment. 



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