§2 CIRCUMSTANCES FAVOftAfcLE TO THE 



but the conditions of life are much more complex from the 

 large number of already existing species ; and if some of 

 these many species become modified and improved, others 

 will have to be improved in a corresponding degree, or they 

 will be exterminated. Each new form, also, as soon as it has 

 been much improved, will be able to spread over the open 

 and continuous area, and will thus come into competition 

 with many other forms. Moreover, great areas, though now 

 continuous, will often, owing to former oscillations of level, 

 have existed in a broken condition ; so that the good effects 

 of isolation will generally, to a certain extent, have con- 

 curred. Finally, I conclude that, although small isolated 

 areas have been in some respects highly favorable for the 

 production of new species, yet that the course of modifica- 

 tion will generally have been more rapid on large areas ; and 

 what is more important, that the new forms produced on 

 large areas, which already have been victorious over many 

 competitors, will be those that will spread most widely, and 

 will give rise to the greatest number of new varieties and 

 species. They will thus play a more important part in the 

 changing history of the organic world. 



In accordance with this view, we can, perhaps, understand 

 some facts which will be again alluded to in our chapter on 

 Geographical Distribution ; for instance, the fact of the 

 productions of the smaller continent of Australia now yield- 

 ing before those of the larger Europseo-Asiatic area. Thus, 

 also, it is that continental productions have everywhere 

 become so largely naturalized on islands. On a small island, 

 the race for life will have been less severe, and there will 

 have been less modification and less extermination. Hence, 

 we can understand how it is that the flora of Madeira, 

 according to Oswald Heer, resembles to a certain extent the 

 extinct tertiary flora of Europe. All fresh-water basins, 

 taken together, make a small area compared with that of the 

 sea or of the land. Consequently, the competition between 

 fresh-water productions will have been less severe than else- 

 where, new forms will have been then more slowly produced, 

 and old forms more slowly exterminated. And it is in fresh- 

 water basins that we find seven genera of Ganoid fishes, 

 remnants of a once preponderant order : and in fresh water 

 we find some of the most anomalous forms now known in 

 the world as the Ornithorhynchus and Lepidosiren, which, 

 like fossils, connect to a certain extent orders at present 

 widely sundered in the natural scale. These anomalous 



