en. xx.] CONDITIONS OF PROGRESS. 283 



enable Evolution in general to result in continuous increase 

 of structural and functional complexity. The present case 

 is, indeed, but a special form of the more general case. 

 How to secure a compromise between fluidity and rigidity is 

 in both cases the essential desideratum. Where the units 

 which make up the aggregate have too much individual 

 freedom of motion, the result is a fluid state in which there 

 is no chance for stable structural arrangements. Where they 

 have too little freedom of motion, the result is a solid state 

 in which there is no chance for structural rearrangements. 

 In the first case, where there is so little dissipation of motion, 

 there is little or no Evolution. In the second case, where so 

 little internal motion is retained, the Evolution which occurs 

 is simply or chiefly a process of consolidation, unattended by 

 any considerable advance from indeterminate uniformity 

 toward determinate multiformity. 



Bearing in mind that we are dealing, not with a mere 

 series of striking analogies, but with a group of real resem 

 blances which result from a fundamental homology between 

 the special process here considered and the more general 

 process which includes it, let us observe that one chief cir 

 cumstance which secures mobility without loss of coherence 

 is a heterogeneous and ever-changing social environment, to 

 the heterogeneous changes of which the community is con 

 tinually required to adjust itself. The illustrations above 

 given unite in showing that where circumstances have 

 afforded such a heterogeneous environment (as a perpetual 

 external excitant of internal rearrangements), the commu 

 nities which have survived through relatively-complete ad- 

 ^ustment have manifested a permanent capacity for progress. 

 Thus is our problem completely connected with the more 

 general problem of natural selection, and with the most 

 general problem of Evolution as manifested in all orders of 

 phenomena. And thus the essential continuity of the pro 

 cesses of Nature is again strikingly illustrated. 



