REVOLUTION VS. EVOLUTION 
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many thrones left vacant by the reptiles, unable to withstand 
the adversities of climatic and physiographic change coupled with 
the ever-increasing ability of their mammalian foes, and soon 
dominated land and sea. Soon thereafter they even aspired to 
the dominion of the air, but in that sphere of activity they have 
thus far failed to rival the birds. 
The conclusion seems unescapable that again the revolutionary 
achievement was merely the climax of a long slow upward 
climb. Had not the preparation of the mammals been complete 
they could scarcely have seized so successfully upon the oppor- 
tunities which opened before them at this time. The conclusion 
is further fortified when we note that the immediate ancestors 
of mammals, the theriodont reptiles, had been in existence 
before the close of the Paleozoic Era, but, though they fore- 
shadowed the mammals in many important particulars of body 
structure, they apparently made no marked response to the 
environmental changes occurring at the close of that era. The 
long preparatory period had but begun for the mammalian 
strains; not yet had they attained the abilities sufficient to 
profit by those changes; that ^ devolution’’ gained them little 
or nothing, simply because they were not ready to take advan- 
tage of it. The inauguration of the mammals as the lords of 
the earth must wait, regardless of ^devolutions,” until the off- 
spring of those theriodents had by the long slow processes of 
evolution completed the training prerequisite to that proud 
position. 
This seems to be the law of life. Revolutions are of little 
avail unless preceded by long and generally agonizing periods of 
preparation. Slowly progressive evolution may lead to a 
spectacular climax of fruition during a moment of organic up- 
heaval, but the attainment is the result of the preparatory 
development, not of the revolutionary forces. Time and again, 
upon the long road so painfully traversed during the geologic 
eras, important milestones have been passed, great upward 
steps have been achieved, unaccompanied by anything remotely 
resembling a ^devolution;” but never, so far as I am aware, has 
any group of animals or plants gained advantages at times of 
