340 



PRINCIPLES OF ANIMAL BIOLOGY 



Darwin was tremondously influenced by the work of the famou? 

 geologist, Sir Charles Lyell (Fig. 234) . Lyell attempted to explain past 

 geological changes by processes going on at the present time. If geolog- 

 ical changes in the past of which we have present day evidence in the form 

 of rock strata, configuration of land surfaces, continental forms, sub- 

 merged islands, and the like, could be explained by such processes as 

 erosion, rising or sinking of the land or sea floor, and volcanic action, 

 which are now going on, Lyell insisted that such explanations should be 

 employed. No processes of a different order from those of the present 

 time should be appealed to unless present day occurrences do not explain. 

 This insistence on the application of modern processes to the explanation 

 of past events is known as the doctrine of uniformitarianism. 



Fig. 233. — Charles Darwin, 1809-1882. {Froin University Magazine. 



Darwin.) 



Photo by Leonard 



Darwin believed that this doctrine could be applied to living organisms 

 as well as to rocks and hills and shore-lines. He had made a voyage 

 around the world, in 1831 to 1836, as naturalist of a surveying party 

 on the ship Beagle. Most of this voyage was devoted to the shores 

 of South America. Darwin had opportunity to make long excursions on 

 land, and observed many remarkable phenomena from which he began 

 to suspect the mutability of species. After he returned from the voyage 

 on the Beagle, he thought it worth while to open a note-book (in 1837) 

 in which he jotted down everj'thing that came to his notice that seemed 

 to bear on the question of the fixity or changeability of species. For 

 twenty years he collected such information as industriously as his health 

 would permit. He had a happy faculty of using others to help him in this 



