82 AUTOBIOGRAPHY. 



the work was worth the consumption of so much 

 time. 



From September 1854 I devoted my whole time to 

 arranging my huge pile of notes, to observing, and to 

 experimenting in relation to the transmutation of 

 species. During the voyage of the Beagle I had been 

 deeply impressed by discovering in the Pampean for- 

 mation 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 supposi- 

 tion that species gradually become modified ; and the 

 .subject haunted me. But it was equally evident that 

 'neither the action of the surrounding conditions, nor 

 the will of the organisms (especially in the case of 

 plants) could account for the innumerable cases in 

 which organisms of every kind are beautifully adapted 

 to their habits of life for instance, a woodpecker or a 

 tree-frog to climb trees, or a seed for dispersal by 

 hooks or plumes. 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. 



