NATURAL SELECTION 149 



reduces the whole theory of evolution to the 

 struggle for life. 



Apropos of this, I have selected some para- 

 graphs from a letter addressed by Darwin to 

 E. Haeckel on the 8th of October 1864 : 



" In South America, three classes of phenomena 

 made a great impression upon me : First, the way 

 in which species closely related succeed and replace 

 one another as one journeys from north to south. 

 Secondly, the proximity of relationship of the 

 species that inhabit the islands of the South 

 American littoral, and those of this continent, a 

 fact that caused me as much surprise as the great 

 variety of species that live in the Galapagos 

 Archipelago close to hand. Thirdly, the close 

 relations that unite the toothless mammals and 

 the rodents of that epoch with the extinct species 

 of the same family. I shall never forget my 

 surprise on disinterring some remains of a gigantic 

 armadillo similar to that of the present day. 



" Reflecting on these facts and comparing them 

 with others of the same order, it seemed possible 

 that the different species that preserve their relation- 

 ship may very well have descended from a common 

 ancestral form. But for several years I have 

 been unable to understand how this form could 

 also have adapted itself to such different conditions 

 of life. I applied myself to the systematic study 



