THEORIES OF ORGANIC EVOLUTION 



structed this powder-mine of facts was Charles Robert 

 Darwin, grandson of the author of Zoonomia. 



As long ago as July i, 1837, young Darwin, then 

 twenty-eight years of age, had opened a private jour- 

 nal, in which he purposed to record all facts that came 

 to him which seemed to have any bearing on the moot 

 point of the doctrine of transmutation of species. 

 Four or five years earlier, during the course of that 

 famous trip around the world with Admiral Fitzroy, 

 as naturalist to the Beagle, Darwin had made the per- 

 sonal observations which first tended to shake his be- 

 lief of the fixity of species. In South America, in the 

 Pampean formation, he had discovered " great fossil 

 animals covered with armor like that on the existing 

 armadillos," and had been struck with this similarity 

 of type between ancient and existing faunas of the same 

 region. He was also greatly impressed by the manner 

 in which closely related species of animals were ob- 

 served to replace one another as he proceeded south- 

 ward over the continent; and "by the South- Amer- 

 ican character of most of the productions of the Gala- 

 pagos 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." 



At first the full force of these observations did not 

 strike him; for, under sway of Ly ell's geological con- 

 ceptions, he tentatively explained the relative absence 

 of life on one of the Galapagos Islands by suggesting 

 that perhaps no species had been created since that 

 island arose. But gradually it dawned upon him that 

 such facts as he had observed " could only be explained 



TOL. nr. i a 



