202 ANNALS NEW YORK ACMU^MY OF SCIENCES 



cies — \vliicli is a question of expansion ui' conii'aeliun uf i'ani;"e. not di- 

 rectly of traiisfereiKC of habitat, although this may be the final result. 

 It seems obvious that the conditions which brought about the early 

 progressiveness of the race in a particular locality would, so far as they 

 were external, cause the continued progressiveness of those individuals 

 Avhich remained in that region ; so far as they were intrinsic, they would 

 affect the main bulk of the race, the center of its range, more than any 

 outlying parts of it. The present writer is very thoroughly convinced 

 that the whole of evolutionaiy progress may be interpreted as a response 

 to external stimuli : and intends here to point out what he regards as the 

 most important of these stimuli. It is therefore necessary to point out 

 tiiat these postulates regarding centers of dispersal and migration are 

 not dependent upon the theories to be proved^ — we are not reasoning in 

 a circle. 



Oceanic and Continental Islands 



J-AIXAL l)lFFi:KE\<'K,S BETWEEN OCEAXTC AND ( 'OXTI \ i:X'l'.\ I. ISI.AXUS 



One of the strongest arguments for the relative permanency of the 

 deep oceans, especially during Cenozoic time, is afforded by the marked 

 and striking contrast between the fauna^ of those large islands which are. 

 and those which are not, included within the continental shelf. The 

 continental islands have the fauna of the continents to which they belong, 

 large as well as small, differing only in the absence of types of recent 

 evolution or of unsuitable adaptation and iii tlie survival of primitive 

 types which have disappeared from the mainland. But no question could 

 be raised as to their former union with tlie mainhmd. no other possible 

 solution would explain their fauna. We are compelled to assume the 

 former connection of the British Isles with Europe, of Ceylon with India, 

 of Japan with Korea or Siberia, of Sumatra, Java and Borneo with the 

 Malayan mainland, of tlie Philippines with Borneo, of Xew Guinea and 

 Tasmania with Australia, of Newfoundland and Cape Breton with Lab- 

 rador and Nova Scotia. In each and all of these cases, the evidence is 

 overwhelming, and, with the exceptions cited, the faunal identity is 

 complete. 



On the other hand, with all those islands which are separated by deep 

 ocean from the mainland, we find that just that evidence is lacking which 

 would afford convincing proof of former union with the mainland. Their 

 faunae are widely different from those of the adjoining mainland : they 

 lack just those animals which could not possibly have reached there 

 except by land bridges; they point often to long periods of independent 

 evolution and expansion, and the primarv' elements of the fauna? of ever}^ 



