Chap. IV. EXTINCTION. 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. 



Extinction. — This subject will be more fully discussed 

 in our chapter on Geology ; 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 

 powers 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. Rarity, 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 



