CHAPTER XVI 



WHAT EVOLUTION IS: THE EVIDENCE UPON 

 WHICH IT RESTS, ETC. 



The preceding pages have been devoted mainly to an 

 account of the shaping of ideas in reference to the architec- 

 ture, the physiology, and the development of animal life. 



We come now to consider a central theme into which all 

 these ideas have been merged in a unified system; viz., the 

 process by which the diverse forms of animals and plants 

 have been produced. 



Crude speculations regarding the derivation of living 

 forms are very ancient, and we may say that the doctrine of 

 organic evolution was foreshadowed in Greek thought. The 

 serious discussion of the question, however, was reserved 

 for the nineteenth century. The earlier naturalists accepted 

 animated nature as they found it, and for a long time were 

 engaged in becoming acquainted merely, with the different 

 kinds of animals and plants, in working out their anatomy 

 and development; but after some progress had been made 

 in this direction there came swinging into their horizon 

 deeper questions, such as that of the derivation of living 

 forms. The idea that the higher forms of life are de- 

 rived from simpler ones by a process of gradual evolution 

 received general acceptance, as we have said before, only 

 in the last part of the nineteenth century, after the work of 

 Charles Darwin; but we shall presently see how the theory 

 of organic development was thought out in completeness by 



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