THE ORIGIN OF SPECIES 37 



by the English Government to survey, for scientific 

 and practical purposes, the southernmost points of 

 South America. The trip lasted five years, and when 

 Darwin returned, the theory of descent was already 

 ripe in his mind. He related this experience in a 

 letter addressed to Haeckel many years later: "In 

 South America three classes of facts were brought 

 strongly before my mind. Firstly, the manner in 

 which closely allied species replace species in going 

 southward. Secondly, the close affinity of the spe- 

 cies inhabiting the islands near South America to 

 those proper to the continent. This struck me pro- 

 foundly, especially the difference of the species in the 

 adjoining islets of Galapagos Archipelago. Thirdly, 

 the relation of the living Edentata and Rodentia to 

 the extinct species. I shall never forget my aston- 

 ishment when I dug out a gigantic piece of armour 

 like that of the living armadillo." 1 



Pondering over these facts and collecting analo- 

 gous ones, Darwin reached the conclusion that spe- 

 cies related to one another might very well be 

 descended from o1ne~"and the same ancestral form, 

 mod^ n£Qhrougnliaap taliojn ^difFprpnfT.«T;??^t on^ 

 ^XLchanged conditions of life. "ThelnuTahility of all 

 living things appe aHJ TgT ^^ that 



mutability and iSe^cTthat acquired modifications 



i October 8, 1S64. Quoted by Haeckel in his Natural History of Cre- 

 ation, 1874, page 119. 





