322 THE COMING OF AGE OF 



about the assumed general extinctions and re-creations 

 of life which are the corresponding biological catas- 

 trophes ? And, if no such interruptions of the ordi- 

 nary 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 neces- 

 sary result of the logical application of the principles 

 of uniformitarianism to the phenomena of life. Dar- 

 win 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 Spe- 

 cies," 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 peo- 

 pled have all descended, each within its own class or 

 group, from common parents, and have all been modi- 

 fied in the course of descent." * 



And, in view of the facts of geology, it follows that 

 all living animals and plants "are the lineal descend- 

 ants of those which lived long before the Silurian 

 epoch." f 



It is an obvious consequence of this theory of descent 

 with modification, as it is sometimes called, that all plants 

 and animals, however different they may now be, must, 

 at one time or other, have been connected by direct 

 or indirect intermediate gradations, and that the ap- 



* " Origin of Species," ed. 1, p. 457. f Ibid. p. 458. 



