NATUEAL SELECTION. 



undulations of the ether and even its existence are hypo- 

 thetical, yet every one now admits the undulatory theory of 

 light. The principle of natural selection may be looked at as 

 a mere hypothesis, but rendered in some degree probable by 

 what we positively know of the variability of organic beings in 

 a state of nature, — by what we positively know of the struggle 

 for existence, and the consequent almost inevitable preser- 

 vation of favourable variations, — and from the analogical for- 

 mation of domestic races. Now this hypothesis may be 

 tested,— and this seems to me the only fair and legitimate 

 manner of considering the whole question,— by trying whether it 

 explains several large and independent classes of "facts; such 

 as the geological succession of organic beings, their distribution 

 in past and present times, and their mutual affinities and 

 homologies. If the principle of natural selection does explain 

 these and other large bodies of facts, it ought to be received. 

 On the ordinary view of each species having been independently 

 created, we gain no scientific explanation of any one of these 

 facts. We can only say that it has so pleased the Creator to 

 command that the past and present inhabitants of the world 

 should appear in a certain order and in certain areas ; that He 

 has impressed on them the most extraordinary resemblances, 

 and has classed them in groups subordinate to groups. But by 

 such statements we gain no new knowledge ; we do not connect 

 together facts and laws ; we explain nothing. 



In a third work I shall try the principle of natural selection 

 by seeing how far it will give a fair explanation of the several 

 classes of facts just alluded to. It was the consideration of 

 these facts which first led me to take up the present subject. 

 VVhen I visited, during the voyage of H.M.S. Beagle, the 

 ^alapagos Archipelago, situated in the Pacific Ocean about 

 500 miles from the shore of South America, I found myself 

 surrounded by peculiar species of birds, reptiles, and plants, 

 existing nowhere else in the world. Yet they nearly all bore 

 an American stamp. In the song of the mocking-thrush, in the 

 narsn cry of the carrion-hawk, in the great candlestick-like 

 ~ ^J P ercei ved the neighbourhood of America, 

 though the is ands were separated by so many miles of ocean 

 irom the mainland, and differed much from it in their geological 



