EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 179 



3. The study of the distribution of species belonging to a single 

 genus reveals that the more primitive or generalized species occupy a 

 central position and the most specialized species are at the outer 

 boundaries of the distributional area. 



4. The faunas and floras of continental islands are just what we 

 should expect on the basis that there was at one time a land connection 

 with the nearest continent; that at this time the faunas and floras were 

 the same on both island and continent; that, later, the continent and 

 island were separated by an impassable barrier of ocean ; and that the 

 inhabitants of the two bodies evolved separately. 



5. The faunas and floras of oceanic islands are like those of the 

 nearest mainland and are of those types, for the most part, that might 

 most readily have been blown there by the wind or carried on floating 

 debris. 



6. The conclusions arrived at by students of geographic distribu- 

 tion, past and present, as to the existence of former land connections, 

 now broken, are borne out by the independent findings of geologists 

 and geographers. 



