314 ON THE ORIGIN OF SPECIES 



in travelling, for instance, from north to south nevei 

 fails to be struck by the manner in which successive 

 groups of beings, specifically distinct, yet clearly re- 

 lated, replace each other. He hears from closely 

 allied, yet distinct kinds of birds, notes nearly similar, 

 and sees their nests similarly constructed, but not quite 

 alike, with eggs coloured in nearly the same manner. 

 The plains near the Straits of Magellan are inhabited 

 by one species of Rhea (American ostrich), and north- 

 ward the plains of La Plata by another species of the 

 same genus ; and not by a true ostrich or emu, like 

 those found in Africa and Australia under the same 

 latitude. On these same plains of La Plata, we see 

 the agouti and bizcacha, animals having nearly the 

 same habits as our hares and rabbits and belonging to 

 the same order of Rodents, but they plainly display 

 an American type of structure. We ascend the lofty 

 peaks of the Cordillera and we find an alpine species 

 of bizcacha ; we look to the waters, and we do not find 

 the beaver or musk-rat, but the coypu and capybara, 

 rodents of the American type. Innumerable other 

 instances could be given. If we look to the islands off 

 the American shore, however much they may differ in 

 geological structure, the inhabitants, though they may 

 be all peculiar species, are essentially American. We 

 may look back to past ages, as shown in the last 

 chapter, and we find American types then prevalent 

 on the American continent and in the American seas. 

 We see in these facts some deep organic bond, prevail- 

 ing throughout space and time, over the same areas of 

 land and water, and independent of their physical con- 

 ditions. The naturalist must feel little curiosity, who 

 is not led to inquire what this bond is. 



This bond, on my theory, is simply inheritance, that 

 cause which alone, as far as we positively know, pro- 

 duces organisms quite like, or, as we see in the case of 

 varieties, nearly like each other. The dissimilarity of 

 the inhabitants of different regions may be attributed 

 to modification through natural selection, and in a quite 

 Bubordinate degree to the direct influence of different 



