PAST AND FUTURE OF ANIMAL LIFE 141 



often said that civilized man is no longer subject 

 to the processes of nature, and is extra-natural, but 

 the same condition has probably been reached over 

 and over again by organisms in a state of nature, 

 which have attained a certain equilibrium with their 

 environment when selection is practically in abeyance. 

 The condition is emphasized in man on account of his 

 immense powers of personal acquisition and adapta- 

 tion, which permit him within wide limits to imitate 

 the process of organic change by a counterfeit similar 

 in every respect save in the essential quality of 

 permanence. 



3. If we are in doubt as to the probability of 

 progress or decline in the future history of mankind, 

 our judgment may be still further perplexed by the 

 existence of a third alternative, which might receive 

 an equal sanction from history and reason. It has 

 been our especial task in the course of these pages 

 to draw attention to examples of animal life still in 

 existence which have remained essentially unchanged 

 for vast though unknown epochs. With the increas- 

 ing knowledge of these persistent types has come 

 from many sides the conviction that the period of 

 time during which life has existed on the earth is 

 immeasurably greater than the earlier evolutionists 

 dared suppose, and that the process of organic change 

 may be incalculably slow and in many instances ar- 

 rested for an indefinitely long period. The attempts 



