LECTURE III 



EVroENCES AND LIMITATIONS 



The purpose of this lecture is to exhibit within brief 

 compass the evidences which are thought to support 

 the theory of a natural evolution of species, and to con- 

 sider whether, and to what extent, we can rightly regard 

 the human species as a product of such evolution. At 

 the outset permit me to remind you again of the dis- 

 tinction between the general theory that existing species 

 have somehow been naturally developed from earlier 

 and simpler ones and the various explanations of this 

 development which Darwin and others have advanced. 

 One may become con\dnced of the futihty of any one, 

 or of all, of these explanations, and yet regard the evi- 

 dence for natural evolution as conclusive. It is this 

 evidence for natural evolution that I now ask you to 

 consider. 



In estimating the evidence of a scientific hypothesis 

 we ought not to expect mathematical demonstration. 

 From the nature of things no demonstrative e\ddence 

 can be had, and its absence will not deter an intelli- 

 gent thinker from accepting a scientific hypothesis which 

 appears to be the best available explanation of the 

 observed facts, and works well. He may indeed accept 

 it provisionally only, while waiting for the results of 



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