1 90 E VOL UTION OF TO-DA Y. 



be able to make any predictions as to oceanic-island 

 life, except to expect that we might find either the 

 same species as those found on the mainland, or 

 some entirely different. But upon the latter suppo- 

 sition, which is, of course, the more probable, and 

 which is practically proved by certain facts, it is per- 

 fectly possible to predict what sort of life would be 

 found. If the islands in question were so related to 

 the mainland by winds and currents, that animals 

 could very readily reach them, their fauna and flora 

 would be expected to be practically the same as 

 those of the neighboring continent, except in the 

 absence of animals which could not cross the water. 

 The species of the island should be all represented 

 by those on the mainland. But when the island is 

 so situated that it cannot be visited except in rare 

 instances, the case will be very different. Here the 

 few animals and plants which occasionally reach the 

 island will be practically isolated from their relatives, 

 the completeness of the isolation depending upon 

 the frequency of immigration of animals from the 

 mainland. Now there is not the slightest doubt 

 that such isolation will produce a very great influ- 

 ence upon the development of species. The de- 

 scendants of these individuals are removed from 

 competition with other species ; they are removed 

 from the certainty of cross-breeding. Under these 

 circumstances every variety will have a chance to 

 perpetuate itself. Having little competition with 

 other animals, even the less favorable varieties will 

 be able to live and reproduce their kind, and not 

 having numerous unmodified individuals to breed 



