306 ANNALS NEW YORK ACADEMY OF SCIENCES 



Among zoological considerations we may mention the following: 



1) The discontinuous distribution of modern species is again and 

 again taken as proof that the regions now inliabited must have been con- 

 nected across deep oceanic basins, without considering the possibility that 

 it is a remnant of a wider past distribution, or that it is due to parallel 

 evolution from a more primitive type of intermediate distribution, now 

 extinct. Yet so many instances are known where the geological record 

 has furnished proof that one or other of these explanations applies to 

 cases of discontinuous distribution, that it would seem that these ought 

 to be the first solutions of the problem to be considered, and that in view 

 of the known imperfection of the geologic record, mere negative evidence 

 is not sufficient to cause them to be set aside. 



2) No account is taken of faunal interchanges often much more ex- 

 tensive, which would presumably have taken place if the land bridges 

 assumed had existed, but which have not taken place. It may here be 

 urged that this too is negative evidence. But the negative evidence de- 

 rived from an appeal to the geological record is weak, not pei- se, but 

 because of the demonstrated imperfection of this record. On the other 

 hand, there are many instances where a land bridge is well proven, and 

 in these cases it is not a few scattered exceptions but an entire fauna 

 that has migrated, subject only to the restrictions imposed by climatic or 

 topographic barriers of other kinds. 



I may venture upon a discussion of a few instances in order to show 

 the type of objections which appear to me to apply to much of the evi- 

 dence cited in favor of most of these transoceanic land bridges. 



On Vain Speculations 



According to some distinguished paleontologists.^-* progress is to be 

 made only by ignoring the possibility that races have originated in or 

 migrated from regions of whose former life we have substantially no 

 record, and assuming that they must have evolved in one or another re- 

 gion where the record is more or less known, and that the actual record 

 must be the sole basis for any conclusions. They refuse to consider the 

 arguments for origin elsewhere, on the ground that such hypotheses are 

 "vain speculations" and "serve merely to conceal our ignorance." 



To this I may answer that a fair and full consideration of the data at 

 hand shows that such hypotheses, of one kind or another, are absolutely 

 necessary, unless we are to abandon all belief in the actuality of evolution 

 and are to treat it as merely a convenient arrangement of successive spe- 



"* Dep6ret, Th^venln and others. 



