AND ITS SELF-CONSERVATION. 275 



earth itself, through its own condensation and conse- 

 quent increasing tension of energy throughout its mass, 

 the differences in the conditions of life on its surface 

 must have continuously become, and cannot for an indefi- 

 nitely extended future cease to become, more and more 

 pronounced. And, as already suggested, and as elabor- 

 ately shown in Darwin's writings, the continuance of life 

 for any type of organisms is possible only through the 

 continuous adaptation of the organisms constituting the 

 type to their environment. Or, as Mr. Spencer puts it: 

 " Life is the continuous adjustment of internal relations 

 to external relations."* And this adaptation must keep 

 pace with whatever changes the environment itself under- 

 goes. Similarly, those that fail of such adaptation can 

 not but become extinct. Fitness to survive consists in 

 fullest correspondence on the part of the living unit to 

 the aspects of Reason constituting the environment of 

 such unit. Since such environment is itself a process, 

 and since it is a constantly varying complex of condi- 

 tions, it is evident that the types of organisms existing 

 in the midst of and dependent upon that constantly 

 varying complex of conditions, must undergo equally 

 constant and corresponding variations as a condition 

 precedent to their survival. The variation of the type 

 that survives can be measured by no less a standard 

 than that of the variation in the environment itself. The 

 longer the period the greater must be the variation in 

 the environment, and hence the greater the variation 

 in the organic types involved. The environment is, 

 indeed, not merely something else than the given unit 

 determined by the environment. It is also, and far more, 



* "Principles of Biology," (N. Y. Ed.) I., 80. 



