RESULTS OF NATURAL SELECTION. 91 



adapted organisms ; and thus new places in the natural 

 economy of the district will be left open to be filled up by 

 the modification of the old inhabitants. Lastly, isolation 

 will give time for a new variety to be improved at a slow 

 rate ; and this may sometimes be of much importance. If, 

 however, an isolated area be very small, either from being 

 surrounded by barriers, or from having very peculiar physical 

 conditions, the total number of the inhabitants will be small ; 

 and this will retard the production of new species through 

 natural selection, by decreasing the chances of favorable 

 variations arising. 



The mere lapse of time by itself does nothing, either for 

 or against natural selection. I state this because it has 

 been erroneously asserted that the element of time has been 

 assumed by me to play an all-important part in modifying 

 species, as if all the forms of life were necessarily under- 

 going 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. 

 Tt likewise tends to increase the direct action of the physical 

 conditions of life, in relation to the constitution 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 Distribution ; 

 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 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 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 supported^ 



