BE8ULTS OF NATURAL 8ELB0TI0N. 97 



fying species, as if all the forms of life were necessarily 

 undergoing change through some innate law. Lapse of 

 time is only so far important, and its importance in this 

 respect is great, that it gives a better chance of beneficial 

 variations arising and of their being selected, accumulated, 

 and fixed. It likewise tends to increase the direct action 

 of the physical conditions of life, in relation to the consti- 

 tution of each organism. 



If we turn to nature to test the truth of these remarks, 

 and look at any small isolated area, such as an oceanic 

 island, although the number of species inhabiting it is 

 small, as we shall see in our chapter on Geographical Dis- 

 tribution; yet of these species a very large proportion are 

 endemic, — that is, have been produced there and nowhere 

 else in the world. Hence an oceanic island at first sight 

 seems to have been highly favorable 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 favorable for the pro- 

 duction of new organic forms, we ought to make the com- 

 parison within equal times; and this we are incapable of 

 doing. 



Although isolation is of great importance in the produc- 

 tion 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 sup- 

 ported, 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 competi- 

 tion 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 conclude that, although small 



