xii 



From March, 1837, then, Darwin, not without many misgivings and 

 fluctuations of opinion, inclined towards transmutation as a pro- 

 visional hypothesis. Three months afterwards he is hard at work 

 coliecting facts for the purpose of testing the hypothesis ; and an almost 

 apologetic passage in a letter to Lyell shows that, already, the attrac- 

 tions of biology are beginning to predominate over those of geology. 



" I have lately been sadly tempted to be idle* — that is, as far as 

 pure Geology is concerned — by the delightful number of new views 

 which have been coming in thickly and steadily — on the classification 

 end affinities and instincts of animals — bearing on the question of 

 species. Note-book after note-book has been filled with facts which 

 begin to group themselves clearly under sub-laws." (I, p. 298.) 



The problem which was to be Darwin's chief subject of occupation 

 for the rest of his life thus presented itself, at first, mainly under its 

 distributional aspect. Why do species present certain relations in 

 space and in time ? Why are the animals and plants of the Gala- 

 pagos Archipelago so like those of South America and yet different 

 from them ? Why are those of the several islets more or less dif- 

 ferent from one another? Why are the animals of the latest geolo- 

 gical epoch in South America similar in fades to those which exist in 

 the same region at the present day, and yet specifically or generi- 

 cally different ? 



The reply to these questions, which was almost universally received 

 fifty years ago, was that animals and plants were created such as they 

 are; and that their present distribution, at any rate so far as terrestrial 

 organisms are concerned, has been effected by the migration of their 

 ancestors from the region in which the ark stranded after the subsi- 

 dence of the deluge. It is true that the geologists had drawn atten- 

 tion to a good many tolerably serious difficulties in the way of the 

 diluvial part of this hypothesis, no less than to the supposition that 

 the work of creation had occupied only a brief space of time. But 

 even those, such as Lyell, who most strenuously argued in favour of 

 the sufficiency of natural causes for the production of the phenomena 

 of the inorganic world, held stoutly by the hypothesis of creation in 

 the case of those of the world of life. 



For persons who were unable to feel satisfied with the fashionable 

 doctrine, there remained only two alternatives — the hypothesis of 

 spontaneous generation, and that of descent with modification. The 

 former was simply the creative hypothesis with the creator left out ; 

 the latter had already been propounded by De Maillet and Erasmus 

 Darwin, among others, and, later, systematically expounded by 



*' Darwin generally uses the word "idle " in a peculiar sense. He means by it 

 working hard at something he likes when he ought to be occupied with a less attrac- 

 tive subject. Though it sounds paradoxical, there is a good deal to be said in favour 

 of this view of pleasant work. 



