Chap. IV.] RESULTS OP NATURAL SELECTION. 129 



island at first sight seems to have been highly favourable 

 for the production of new species. But we may thus de- 

 ceive 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 spe- 

 cies 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, a^d will thus come into com- 

 petition with many other forms. Moreover, great areas, 

 though now continuous, will often, owing to former os- 

 cillations of level, have existed in a broken condition; so 

 that the good effects of isolation will generally, to a cerr 

 tain 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 al- 



