A HISTORY OF SCIENCE 



on the supposition that species gradually become modi- 

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

 subject 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 Zoonomia and The 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 

 similar 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 mind was open and receptive; he was eager only 

 for facts which might lead him to an understanding of 

 a problem which seemed utterly obscure. It was some- 

 thing to feel sure that species have varied; but how 

 have such variations been brought about? 



It was not long before Darwin found a clew which he 

 thought might lead to the answer he sought. In cast- 

 ing about for facts he had soon discovered that the 

 most available field for observation lay among domesti- 

 cated animals, whose numerous variations within spe- 

 cific lines are familiar to every one. Thus under do- 

 mestication creatures so tangibly different as a mastiff 



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