iv MODERN EVOLUTION 121 



The details of that voyage, the first of the two 

 memorable events in Darwin's otherwise unadventur- 

 ous life, are set down in delightful narrative in his 

 Naturalists Voyage Round the World, and it will suffice 

 to quote a passage from the autobiography bearing 

 on the significance of the materials collected during 

 his five years' absence. 



During the voyage of the Beagle I had been deeply 

 impressed by discovering in the Pampean formation great 

 fossil animals covered with armour like that on the existing 

 armadillos ; secondly, by the manner in which closely allied 

 animals replace one another in proceeding southwards over 

 the continent ; and thirdly, by the South American character 

 of most of the productions of the Galapagos Archipelago, 

 and more especially by the manner in which they differ 

 slightly on each island of the group, none of the islands 

 appearing to be very ancient in a geological sense. It was 

 evident that such facts as these, as well as many others, 

 could only be explained on the supposition that species 

 gradually became modified ; and the subject haunted me. 

 But it was equally evident that ' none of the evolutionary 

 theories then current in the scientific world ' could account 

 for the innumerable cases in which organisms of every kind 

 are beautifully adapted to their habits of life. ... I had 

 always been much struck by such adaptations, and until 

 these could be explained, it seemed to me almost useless 

 to endeavour to prove by indirect evidence that species 

 have been modified. ... In October 1838, that is, 

 fifteen months after I had begun my systematic inquiry, I 

 happened to read for amusement Malthus on Population, 

 and being well prepared to appreciate the struggle for 

 existence which everywhere goes on, from long-continued 

 observations of the habits of plants and animals, it at 

 once struck me that under these circumstances favourable 

 variations would tend to be preserved, and unfavourable 

 ones destroyed. The result of this would be the formation 

 of new species. 



