No. 554] FITNESS OF ENVIRONMENT 



pear to be related to complexity, regulation and meta- 

 bolism. 



There are no other compounds which share more than 

 a smajl part of the qualities of fitness of water and car- 

 bonic acid, no other elements which share those of car 

 bon, hydrogen and oxygen. 



None of the characteristics of these substances are 

 known to be unfit, or seriously inferior to the same char- 

 acteristics in any other substance. 



Therefore the fitness of the environment is both real 

 and unique. 



In drawing this final conclusion I mean to assert the 

 following propositions : 



I. The fitness of the environment is one part of a re- 

 ciprocal relationship of which the fitness of the organ- 

 ism is the other. This relationship is completely and 

 perfectly reciprocal; the one fitness is not less important 

 than the other, nor less invariably a constituent of a 

 particular case of biological fitness; it is not less fre- 

 quently evident in the characteristics of water, carbonic 

 acid and the compounds of carbon, hydrogen and oxy- 

 gen than is fitness from adaptation in the characteristics 

 of the organism. 



II. The fitness of the environment results from char- 

 acteristics which constitute a series of maxima— unique 

 or nearly unique properties of water, carbonic acid, the 

 compounds of carbon, hydrogen and oxygen and the 

 ocean— so numerous, so varied, so nearly complete 

 among all things which are concerned in the problem that 

 together they form certainly the greatest possible fit- 

 ness. No other environment consisting of primary con- 

 stituents made up of other known elements, or lacking 

 water and carbonic acid, could possess a like number of 

 fit characteristics or such highly fit characteristics, or in 

 any manner such great fitness to promote complexity, 

 durability and active metabolism in the organic mechan- 

 ism which we call life. 



It must not be forgotten that the possibility of such 

 conclusions depends upon the universal character of 



