EVIDENCE FROM DISTRIBUTION 145 



belong to peculiar species, but all are of South 

 American type and have their nearest relatives in 

 that continent. Each of the larger islands of the 

 group has species peculiar to itself, but almost all 

 the species distributed on the various islands belong 

 to the same or nearly allied genera, and thus to- 

 gether form a homogeneous and closed group. The 

 explanation which Darwin gave to the phenomena 

 still remains the most satisfactory that has been 

 offered. The distance from the mainland is so great, 

 that for any bird or lizard to reach the islands must 

 always have been a rare event, but a few species did 

 arrive and were thus practically cut off from their 

 relatives, of the continent. Communication be- 

 tween the different islands is likewise rare and so 

 each became the seat of a little colony which gradu- 

 ally changed from its former condition to form races, 

 varieties and eventually species. Thus, the evolu- 

 tionary theory accounts for the facts in a simple 

 and adequate manner, while the rival theory offers 

 no explanation. The Cape Verde Islands, off the 

 west coast of Africa are a volcanic group quite like 

 the Galapagos, but their animals are of African 

 type modified through isolation and the Galapagos 

 kind of distribution is not the exception, but the 

 rule under similar conditions. 



Whether new species, say of birds, will arise in 

 an oceanic island, depends on the frequency with 

 which mainland birds can visit it and thus by con- 

 stant crossing maintain the continental character- 



