NATURAL SELECTION 83 



forms, we ought to make the comparison within equal times; and 

 this we are incapable of doing. 



Although isolation is of great importance in the production of 

 new species, on the whole I am inclined to believe that largeness 

 of area is still more important, especially for the production of 

 species which shall prove capable of enduring for a long period, 

 and of spreading widely. Throughout a great and open area, not 

 only will there be a better chance of favorable variations, arising 

 from the large number of individuals of the same species there 

 supported, 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 exter- 

 minated. Each new form, also, as soon as it has been much im- 

 proved, will be able to spread over the open and continuous area, 

 and will thus come into competition with many other forms. More- 

 over, 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 concurred. Finally, I conclude that, although small isolated 

 areas have been in some respects highly favorable for the produc- 

 tion of new species, yet that the course of modification will gen- 

 erally have been more rapid on large areas; and what is more im- 

 portant, that the new forms produced on large areas, which al- 

 ready 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 ot the productions of the 

 smaller continent of Australia now yielding before those of the 

 larger Europaeo-Asiatic area. Thus, also, it is that continental pro- 

 ductions 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 ex- 

 tinct tertiary flora of Europe. All fresh-water basins, taken to- 

 gether, make a small area compared with that of the sea or of 

 the land. Consequently, the competition between fresh-water pro- 

 ductions will have been less severe than elsewhere, new forms will 

 have been then more slowly produced, and old forms more slowly 



