136 DOCTRINE OF EVOLUTION 



known in his student days tending to prove that organic 

 evlution was a real natural process. LyelPs doctrine 

 of uniform geological history made an early and deep 

 impression upon his mind, and it led him to ask himself 

 whether the efficient causes of past evolution might 

 not be revealed by an analysis of the present workings 

 of nature. As naturalist of the " Beagle " during its 

 four years' cruise around the world, Darwin saw many 

 new lands and observed varied circumstances under 

 which the organisms of the tropics and other regions 

 lived their lives. The fierce struggle for existence 

 waged by the denizens of the jungle recalled to him 

 the views of Malthus regarding overpopulation and 

 its results. These and other influences led him to 

 begin the remarkable series of note-books, from which 

 it is interesting indeed to learn how the doctrine of 

 natural selection began to assume a definite and per- 

 manent form in his mind, as year followed year, and 

 evidence was added to evidence. And it is a valuable 

 lesson to the student of science that for twenty-five years 

 Darwin devoted all his time to the acquisition of facts 

 before he gave his doctrine to the world in the famous 

 " Origin of Species." 



Darwin was particularly impressed by the way 

 mankind has dealt with the various species of domesti- 

 cated animals, and he was the first naturalist to 

 point out the correspondence between the breeder's 

 method of " artificial selection/' and the world- wide 

 process of natural selection. As every one knows, the 

 breeder of race horses finds that colts vary much in their 

 speed; discarding the slower animals, he uses only 

 the swifter for breeding purposes, and so he perfects 



