1 INTRODUCTION. 



500 miles from 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 

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

 opuntias, I clearly perceived the neighbourhood of America, 

 though the islands were separated by so many miles of ocean 

 from the mainland, and differed much in their geological 

 constitution and climate. Still more surprising was the fact 

 that most of the inhabitants of each separate island in this 

 small archipelago were specifically different, though most 

 closely related to each other. The archipelago, with its 

 innumerable craters and bare streams of lava, appeared to 

 be of recent origin ; and thus I fancied myself brought near 

 to the very act of creation. I often asked myself how these 

 many peculiar animals and plants had been produced : the 

 simplest answer seemed to be that the inhabitants of the 

 several islands had descended from each other, undergoing 

 modification in the course of their descent ; and that all the 

 inhabitants of the archipelago were descended from those of 

 the nearest land, namely America, whence colonists would 

 naturally have been derived. But it long remained to me an 

 inexplicable problem how the necessary degree of modification 

 could have been effected, and it would have thus remained 

 for ever, had I not studied domestic productions, and thus 

 acquired a just idea of the power of Selection. As soon as I 

 had fully realized this idea, I saw, on reading Malthus on 

 Population, that Natural Selection was the inevitable result 

 of the rapid increase of all organic beings ; for I was prepared 

 to appreciate the struggle for existence by having long 

 studied the habits of animals. 



Before visiting the Galapagos I had collected many animals 

 whilst travelling from north to south on both sides of America, 

 and everywhere, under conditions of life as different as it is 

 possible to conceive. American forms were met with — species 

 replacing species of the same peculiar genera. Thus it was 

 when the Cordilleras were ascended, or the thick tropical 

 forests penetrated, or the fresh waters of America searched. 

 Subsequently I visited other countries, which in all then 



