52; 
But we will assume, for the sake of argument, that a 
species does increase in numbers in consequence of the 
tendency to increase in a geometrical ratio, and that some 
members of the species are compelled to emigrate. By 
no manner of means does it follow in that case that they 
will find an unoccupied sphere ready for their reception. 
On the contrary, Mr. Darwin assures us that— 
“ under nature the individuals of the same species . . . are 
rigorously kept to their proper places by a host of competing animals 
and plants.”—(The Variation, vol. ii., ft. 254.) 
The consequence of this state of things is apt to be fatal 
to the pioneers of an emigrant species. 
“ Each species on the confines of its range, where it exists in 
lessened numbers, will, during fluctuations in the number of its 
enemies, or of its prey, or in the nature of the seasons, be extremely 
liable to utter extermination.”—(Origin of Sftecies. ftft. 133-6.) 
If there has been a tendency to increase in a geometrical 
ratio within the range of a given species, there may be the 
same tendency in the other species which inhabit the 
contiguous territory, and the emigrants might then afford 
the needed food for the growing numbers of the carnivora; 
or there would be no room for more ruminants where 
ruminants already abounded. Nor would they be any 
better off if the contiguous sphere were already occupied 
by a stationary population due to an already existing 
competition. Clearly, if the circumstances were the same 
which now exist, according to Darwinian writers, emigra 
tion would be beset with difficulty. 
But let us suppose that the conditions were different— 
let us grant that the species were not hindered in their 
desire to spread, and that the contiguous region was not 
fully occupied. Then, if the locality were precisely