548 THE EVOLUTION OF LIFE. 



or the maintenance of a balance between the forces to which 

 an organism is subject and the forces which it evolves. Hence 

 all changes which enable a species to live under altered con 

 ditions, are changes towards equilibrium with the altered 

 conditions; and therefore those which do not come within 

 the class of direct equilibrations, must come within the class 

 of indirect equilibrations. 



And now we reach an interpretation of Natural Selection 

 regarded as a part of Evolution at large. As understood in 

 First Principles, Evolution is a continuous redistribution of 

 matter and motion; and a process of evolution which is not 

 expressible in terms of matter and motion has not been 

 reduced to its ultimate form. The conception of Natural 

 Selection is manifestly one not known to physical science: 

 its terms are not of a kind physical science can take cognis 

 ance of. But here we have found in what manner it may 

 be brought within the realm of physical science. Eejecting 

 metaphor we see that the process called Natural Selection is 

 literally a survival of the fittest; and the outcome of the 

 above argument is that survival of the fittest is a maintenance 

 of the moving equilibrium of the functions in presence of 

 outer actions : implying the possession of an equilibrium 

 which is relatively stable in contrast with the unstable 

 equilibria of those which do not survive. 



