THE CENTURY'S PROGRESS IN BIOLOGY 



place one another as he proceeded southward over the 

 continent ; and " 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." 



At first the full force of these observations did not 

 strike him ; for, under sway of Lyell'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 isl- 

 and arose. But gradually it dawned upon him that 

 such facts as he had observed "could only be explained 

 on the supposition that species gradually become modi- 

 fied." From then on, as he afterwards asserted, the sub- 

 ject haunted him ; hence the journal of 1837. 



It will thus be seen that the idea of the variability of 

 species came to Charles Darwin as an. inference from 

 personal observations in the field, not as a thought bor- 

 rowed from books. He had, of course, read the works 

 of his grandfather much earlier in life, but the argu- 

 ments of the Zoonomia and Temple of Nature had not 

 served in the least to weaken his acceptance of the cur- 

 rent belief in fixity of species. Nor had he been more 

 impressed with the doctrine of Lamarck, so closely sim- 

 ilar to that of his grandfather. Indeed, even after his 

 South American experience had aroused him to a new 

 point of view he was still unable to see anything of 

 value in these earlier attempts at an explanation of the 

 variation of species. In opening his journal, therefore, 

 he had no preconceived notion of upholding the views of 

 these or any other makers of hypotheses, nor at the 

 time had he formulated any hypothesis of his own. His 



