Chap. IV. 
EXTINCTIOlsr. 
109 
tent action of natural selection accords perfectly well 
with what geology tells us of the rate and manner at 
which the inhabitants of this world have changed. 
Slow though the process of selection may be, if feeble 
man can do much by his powers of artificial selection, 
I can see no limit to the amount of change, to the 
beauty and infinite complexity of the coadaptations 
between all organic beings, one with another and with 
their physical conditions of life, which may be effected in 
the long course of time by nature’s power of selection. 
JExtinction ,—This subject will be more fully discussed 
in our chapter on G-eology ; but it must be here alluded 
to from being intimately connected with natural selec¬ 
tion. Natural selection acts solely through the pre¬ 
servation of variations in some way advantageous, which 
consequently endure. But as from the high geometrical 
ratio of increase of all organic beings, each area is 
already fully stocked with inhabitants, it follows that 
as each selected and favoured form increases in number, 
so will the less favoured forms decrease and become 
rare. Earity, as geology tells us, is the precursor to 
extinction. We can, also, see that any form repre¬ 
sented by few individuals will, during fluctuations 
in the seasons or in the number of its enemies, run 
a good chance of utter extinction. But we may go 
further than this ; for as new forms are continually 
and slowly being produced, unless we believe that the 
number of specific forms goes on perpetually and almost 
indefinitely increasing, numbers inevitably must be¬ 
come extinct. That the number of specific forms has 
not indefinitely increased, geology shows us plainly; 
and indeed we can see reason why they should not 
have thus increased, for the number of places in the 
polity of nature is not indefinitely great,—not that we 
