96 ON THE ORIGIN OF SPECIES 



for to ascertain whether a small isolated area, or a 

 large open area like a continent, has been most favour- 

 able for the production of new organic forms, we ought 

 to make the comparison within equal times ; and this 

 we are incapable of doing. 



Although I do not doubt that isolation is of consider- 

 able importance in the production of new species, on 

 the whole I am inclined to believe that largeness of 

 area is of more importance, more especially in the 

 production of species, which will 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 favourable variations arising from 

 the large number of individuals of the same species 

 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 oscilla- 

 tions of level, will often have recently 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 

 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 



