232 THE COMING OF AGE OF vil 



day. No physical geologist now dreams of seeking, 

 outside the range of known natural causes, for the 

 explanation of anything that happened millions of 

 years ago, any more than he would be guilty 

 of the like absurdity in regard to current events. 



The effect of this change of opinion upon biolo- 

 gical speculation is obvious. For, if there have 

 been no periodical general physical catastrophes, 

 what brought about the assumed general ex- 

 tinctions and re-creations of life which are the 

 corresponding biological catastrophes ? And, if no 

 such interruptions of the ordinary course of nature 

 have taken place in the organic, any more than in 

 the inorganic, world, what alternative is there to 

 the admission of evolution ? 



The doctrine of evolution in biology is the 

 necessary result of the logical application of the 

 principles of uniformitarianism to the phenomena 

 of life. Darwin is the natural successor of Hutton 

 and Lyell, and the " Origin of Species " the logical 

 sequence of the " Principles of Geology." 



The fundamental doctrine of the " Origin of 

 Species," as of all forms of the theory of evolution 

 applied to biology, is " that the innumerable 

 species, genera, and families of organic beings with 

 which the world is peopled have all descended, 

 each within its own class or group, from common 

 parents, and have all been modified in the course of 

 descent." l 



1 Origin of Species, ed. 1, p. 457. 



