PRINCIPAL ATTEMPTS AT EXPLANATION 157 



2. Darwinism and neo-Darwinism. 

 (1) Darwinism. 



(i) Darwin's Doctrine. Charles Robert Darwin, as 

 scientific associate, accompanied an expedition to 

 America on board the Beagle in the year 1831. Two 

 observations which he made there gave him particular 

 food for thought. 1 



In the plains of La Plata and Patagonia he discovered 

 fossil remains of gigantic Sloths (Edentata = toothless), 

 especially of Dasypus gigas. Might not the small living 

 forms of the Sloth, which are now exclusively found 

 in South America, be the offspring of those gigantic 

 forms ? In that case they would certainly have been 

 considerably altered. 



The farther he went from North to South, so much 

 the more it struck him how, particularly the Birds 

 (he was an ornithological expert), but also other animals, 

 gradually assumed a somewhat different appearance. 

 Might not this difference be a simple result of somewhat 

 changed environments ? In that case the organisms 

 were again variable, and again this was due to the 

 influence of external environmental conditions. 



Full three and thirty years he employed after his 

 return (1836) in experimenting that is, by breeding 

 to demonstrate the variability of organisms and discover 

 the principle by which this variability was governed in 



1 See as regards the following remarks the excellent report of R. de 

 Sinety, S. J. : Un demi-siecle de Darwinisms (Revue des Questions scientifiques, 

 1910). 



