PREFACE 



Darwinian fitness is compou nded of a 

 mutual relationship between the organism 

 and the environment. Of this, fitness of en- 

 vironment is quite as essential a component as 

 the fitness which arises in the process of or- 

 ganic evolution ; and in fundamental charac- 

 teristics the actual environment is the fittest 



possible abode of life^ Such is the thesis 



which the present volume seeks to establish. 

 This is not a novel hypothesis. In rudimen- 

 tary form it has already a long history behind 

 it, and it was a familiar doctrine in the early 

 nineteenth century. It presents itself anew 

 as a result of the recent growth of the science 

 of physical chemistry. 



About fifteen years ago I firs t became i nter- 

 ested "m~tlie eumie~ction _be tween physi cal, and 

 chemical properti es of sim plesubstances and 

 the organic fu nctions which t hey serve. At 

 that time the applications of the new physical 

 chemistry to physiology were only just begin- 

 ning, and the older speculations of natural 

 theology upon such subjects had long since 



