loS CHARLES DARWIN 



varied situations. On the burning plains of La Plata 

 we get the agouti and the bizcacha as the chief rodents'; 

 we ascend the Cordillera, and close to the eternal snows 

 we discover, not hares and rabbits like those of Europe, 

 but a specialised chilly mountain form of the same 

 distinctly South American type. We turn to the 

 rivers, and we see no musk-rat or beaver, but the 

 coypu and capybara, slightly altered varieties of the 

 original bizcacha ancestor. Australia has no wolf, but 

 it has instead fierce and active carnivorous marsupials ; 

 it has no mice, but some of its tiny kangaroo-like 

 creatures fulfil analogous functions in its animal 

 economy. Everywhere the evidence points to the con- 

 clusion that local species have been locally evolved from 

 pre-existing similar species. The oceanic isles, of which 

 Darwin had had so large an experience, and especially 

 his old friends the Galapagos, come in usefully for this 

 stage of the question. They are invariably inhabited, 

 as Darwin pointed out, and as Wallace has since 

 abundantly shown in the minutest detail, by waifs 

 and strays from neighbouring continents, altered and 

 specialised by natural selection in accordance with the 

 conditions of their new habitat. As a rule, they point 

 back to the districts whence blow the strongest and 

 most prevalent winds ; and the modifications they have 

 undergone are largely dependent upon the nature of 

 the other species with which they have to compete, or 

 to whose habits they must needs accommodate them- 

 selves. In such cases it is easy to see how far Darwin's 

 special conception of natural selection helps to explain 

 and account for facts not easily explicable by the older 

 evolutionism of mere descent with modification. 



