106 CIRCUMSTANCES FAVOURABLE Chap. IV. 



there supported, but the conditions of life are infinitely 

 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 im- 

 proved, will be able to spread over the open and con- 

 tinuous area, and will thus come into competition with 

 many others. Hence more new places will be formed, 

 and the competition to fill them will be more severe, on 

 a large than on a small and isolated area. Moreover, 

 great areas, though now continuous, owing to oscillations 

 of level, will often have recently existed in a broken con- 

 dition, so that the good effects of isolation will generally, 

 to a certain extent, have concurred. Finally, I conclude 

 that, although small isolated areas probably 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, will give rise to most new varieties and species, 

 and will thus play an important part in the changing 

 history of the organic world. 



We can, perhaps, on these views, understand some 

 facts which will be again alluded to in our chapter on 

 geographical distribution ; for instance, that the pro- 

 ductions of the smaller continent of Australia have 

 formerly yielded, and apparently are now yielding, 

 before those of the larger Europaeo- 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 exter- 



