EVIDENCE OF FOSSIL RKMAIXS 105 



graphical discontinuity on the one hand and a faunal 

 peculiarity on the other that reinforces our confidence 

 in the evolutionary interpretation of the facts of distri- 

 bution. 



It is true that the various classes of animals do not 

 always appear with coextensive ranges, llie barriers 

 between two groups of related s])ecies will not be the 

 same in all cases. A range like the Rocky Mountains 

 will keep fresh-water fish apart, while birds and mam- 

 mals can get across somewhere at some time. All 

 these things must be taken into account in analyzing 

 the phenomena of distribution, and many factors must 

 be given due attention ; but in all cases the reasons for 

 the particular state of affairs hi geographical and 

 biological respects possess an evolutionary significance. 



Having then all the facts of animal natural history 

 at his disposal, and the uniform prinei])les in each 

 body of fact that demonstrate evolution, it is small 

 wonder that the evolutionist seems to dogmatize when 

 he asserts that descent with adaptive and divergent 

 modification is true for all species of living things. 

 The case is complete as it stands to-day, while it is 

 even more significant that every new discovery falls 

 into line with what is already known, and takes its 

 natural place in the all-inclusive doctrine of organic 

 evolution. Because this explanation of the characteris- 

 tics of the living world is more reasonable than any 

 other, science teaches that it is true. 



