Chap. IV. 
TO NATUEAIi SELECTION. 
105 
tions in their structure and constitution. Lastly, isola¬ 
tion, by checking immigration and consequently com¬ 
petition, will give time for any new variety to be slowly 
improved; and this may sometimes be of importance in 
the production of new species. If, however, an isolated 
area be very small, either from being surrounded by 
barriers, or from having very peculiar physical condi¬ 
tions, the total number of the individuals supported on 
it will necessarily be very small; and fewness of indivi¬ 
duals will greatly retard the production of new species 
through natural selection, by decreasing the chance of 
the appearance of favourable variations. 
If we turn to nature to test the truth of these re¬ 
marks, and look at any small isolated area, such as an 
oceanic island, although the total number of the species 
inhabiting it, will be found to be small, as w^e 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. Hence 
an oceanic island at first sight seems to have been 
highly favourable for the production of new species. 
But we may thus greatly deceive ourselves, for to ascer¬ 
tain whether a small isolated area, or a large open area 
like a continent, has been most favourable for the produc¬ 
tion of new organic forms, we ought to make the compari¬ 
son within equal times; and this we are incapable of doing. 
Although I do not doubt that isolation is of consider¬ 
able importance in the production of new species, on 
the whole I am inclined to believe that largeness of 
area is of more importance, more especially in the 
production of species, which will 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 
F 3 
