Chap. iv. Results of Natural Selection. 



8.3 



better chance of favourable 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 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 concurred. Finally, I conclude that, 

 although small isolated areas have been in some respects highly 

 favourable for the production of new species, yet that the course of 

 modification 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 yielding before those of the larger 

 Europa3o-Asiatic area. Thus, also, it is that continental productions 

 have everywhere become so largely naturalised 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 elsewhere ; new forms will have been then more slowly 

 produced, and old forms more slowly exterminated. And it is in 

 iresn-water basins that we find seven genera of Ganoid fishes, 

 remnants of a once preponderant order : and in fresh water we find 

 some ot the most anomalous forms now known in the world, as the 

 ll . Y ^ US ? d Le P idosireil > which, like fossils, connect to a 

 sc e t£ ? at preSent widel y sundered * the natural 



have'end^% a T US f0mS may be Called H ™S foss ^ they 

 nave endured to the present day, from having inhabited a confined 



g 2 



