CHAPTER VIII 

 LIFE AND THE COSMOS 



THE SIGNIFICANCE OF FITNESS 



A HALF century has passed since Darwin 

 wrote "The Origin of Species," and once 

 again, but with a new aspect, the relation 

 between life and the environment presents 

 itself as an unexplained phenomenon. The 

 problem is now far different from what it was 

 before, for adaptation has won a secure posi- 

 tion among the greatest of natural processes, 

 a position from which we may suppose it is 

 certainly never to be dislodged ; and natural 

 selection is its instrument, even if, as many 

 think, not the only one. 1 Yet natural selec- 



1 Natural selection remains still a vera causa in the origin 

 of species; but the function ascribed to it is practically 

 reversed. It exchanges its former supremacy as the supposed 

 sole determinant among practically indefinite possibilities 

 of structure and function, for the more modest position of 

 simply accelerating, retarding, or terminating the process of 

 otherwise determined change. It furnishes the brake rather 

 than the steam or the rails for the journey of life ; or in better 



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