NATURAL SELECTION 153 



duction 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 modi- 

 fied 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 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 concliLde that, although small 

 isolated areas have been in some respects highly favor- 

 able 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, under- 

 stand some facts which will be again alluded to in our 



