SPECIAL CREATION OR DERIVATION? 



just the reverse. Again ther^ is no apprecia- 

 ble difference between the conditions of exists 

 ence in the seas east and west of the isthmus 

 of Panama ; and, according to the assumption 

 of the special-creationists, their marine faunas 

 ought to be almost exactly alike. In fact no 

 two marine faunas are more completely distinct. 

 Hardly a fish, mollusk, or crustacean is com- 

 mon to the eastern and western shores. This 

 is because the isthmus, though narrow, is im- 

 passable for marine organisms. On the other 

 hand, wherever groups of organisms are not pre- 

 vented by impassable barriers from spreading 

 over wide tracts of country or of sea, we find 

 distinct but closely allied species widely spread 

 and living among the most diverse conditions. 

 The inference is obvious that the population of 

 different zoological and botanical areas is due to 

 migration, and not to special creation. Where 

 organisms have a chance to migrate, they mi- 

 grate and become adapted, by slight specific 

 changes, to the new circumstances which they 

 encounter. But where there is a barrier between 

 one area and another, there we find complete 

 diversity between the inhabitants of the two 

 areas, although there is no reason for such 

 diversity, save the impossibility of getting across 

 the barrier. Of like meaning is the fact that 

 batrachians and terrestrial mammals are never 

 found indigenous upon oceanic islands'. As 

 407 



