102 pQCTpmE OF EVOLUTION 



The general principles of distribution appear with 

 greatest clearness when an examination is made of 

 the animals and plants of isolated regions like islands. 

 The Galapagos Islands constitute a group that has 

 figured largely in the literature of the subject, partly 

 because Darwin himself was so impressed by what he 

 found there in the course of his famous voyage around the 

 world in the " Beagle." They form a cluster on the 

 Equator about six hundred miles west of the nearest 

 point of the neighboring coast of South America. 

 Although the lizards and birds that live in the group 

 differ somewhat among themselves as one passes from 

 island to island, on the whole they are most like the 

 species of the corresponding classes inhabiting South 

 America. Why should this be so? On the hypothesis 

 of special creation there is no reason why they should 

 not be more like the species of Africa or Australia than 

 like those of the nearest body of the mainland. The 

 explanation given by evolution is clear, simple, and 

 reasonable. It is that the characteristic island forms 

 are the descendants of immigrants which in greatest 

 probability would be wanderers from the neighboring 

 continent and not from far distant lands. Reaching 

 the isolated area in question the natural factors of 

 evolution would lead their offspring of later generations 

 to vary from the original parental types, and so the 

 peculiar Galapagos species would come into being. 

 The fact that the organisms living on the various 

 islands of this group differ somewhat in lesser details 

 adds further justification for the evolutionary inter- 

 pretation, because it is not probable that all the isl- 

 ands would be populated at the same time by similar 



