THE ORIGIN OF SPECIES 369 



population, and the differences between the existing species 

 are such as one might expect to find among the members of a 

 genus long isolated in different environments by geographical 

 barriers. We know, for example, that a litter of European 

 Rabbits was introduced on the small island of Porto Santo 

 during the fifteenth century and by the middle of the last 

 century its descendants had become so distinct from the 

 parent form that it was described as a 'new species.' 



As a matter of fact the characteristic fauna of islands 

 was what impressed Darwin with the need of some interpre- 

 tation other than special creation. During his famous three 

 years' voyage around the world on the " Beagle," he stopped 

 at the Galapagos Islands, situated about 600 miles off the 

 west coast of South America, and was astonished to find that 

 although the fauna as a whole resembled fairly closely that 

 of the mainland, nevertheless the species for the most part 

 not only were different, but even those of the separate islands 

 were distinct the islands nearest to each other having 

 species most similar. Darwin wrote, "My attention was 

 first thoroughly aroused by comparing together the numerous 

 specimens, shot by myself and several others on board, of 

 Mocking Thrushes, when, to my astonishment, I discovered 

 that all those from Charles Island belonged to one species 

 (Mimus trifasciatus) ; all from Albemarle Island to M. par- 

 vulus] and all from James and Chatham Islands (between 

 which two other islands are situated as connecting links) 

 belonged to M. melanotis." 



Darwin's observations of such facts as these have been 

 corroborated in the Galapagos and extended to isolated 

 island faunas and floras all over the world. And further, his 

 explanation of the phenomena is the most plausible extant. 

 Continental islands secure their life from the mainland before 

 they are cut off, and Oceanic islands after their formation by 



