100 EXTINCTION BT NA TURKL 8ELEGIT0N. 



neutralize the power of natural selection. I do not believe 

 so. But I do believe that natural selection will generally 

 act very slowly, only at long intervals of time, and only on 

 a few of the inhabitants of the same region. I further 

 believe that these slow, intermittant results accord well 

 with what geology tells us of the rate and manner at which 

 the inhabitants of the world have changed. 



Slow though the process of selection may be, if feeble 

 man can do much by artificial selection, I can see no limit 

 to the amount of change, to the beauty and complexity of 

 the coadaptations between all organic beings, one with 

 another and with their physical conditions of life, which 

 may have been affected in the long course of time through 

 nature's power of selection, that is by the survival of the 

 fittest. 



EXTINCTION CAUSED BY NATUEAL SELECTION. 



This subject will be more fully discussed in our chap- 

 ter on Geology; but it must here be alluded to from 

 being intimately connected with natural selection. Nat- 

 ural selection acts solely through the preservation of vari- 

 ations in some way advantageous, which consequently en- 

 dure. Owing to the high geometrical rate of increase of 

 all organic beings, each area is already fully stocked with 

 inhabitants; and it follows from this, that as the favored 

 forms increase in number, so, generally, will the less fa- 

 vored decrease and become rare. Earity, as geology tells 

 us, is the precursor to extinction. We can see that any 

 form which is represented by few individuals will run a 

 good chance of utter extinction, during great fluctuations 

 in the nature or the seasons, or from a temporary increase 

 in the number of its enemies. But we may go further than 

 this; for, as new forms are produced, unless we admit that 

 specific forms can go on indefinitely increasing in number, 

 many old forms must become extinct. That the number 

 of specific forms has not indefinitely increased, geology 

 plainly tells us; and we shall presently attempt to show 

 why it is that the number of species throughout the world 

 has not become immeasurably great. 



We have seen that the species which are most numer- 

 ous in individuals have the best chance of producing favor- 



