Chap. IT.] RESULTS OF NATURAL SELECTION. 129 



first sight seems to have been highly favourable for the 

 production of new species. But we may thus deceive 

 ourselves, for to ascertain whether a small isolated area, 

 or a large open area like a continent, has been most 

 favourable for the production of new organic 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 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 con- 

 curred. 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 modi- 

 fication 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 



