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 
345 
