NATURAL SELECTION 99 



same region at the same time. I further believe, that 

 this very slow, intermittent 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 

 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. 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 in- 

 definitely increasing, numbers inevitably must become 

 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 ha\*e 

 thus increased, for the number of places in the polity 

 of nature is not indefinitely great, — not that we have 

 any means of knowing that any one region has as yet got 

 its maximum of SDecies. Probably no region is as yet 



