166 THE ORIGIN OF SPECIES 



,olcl inhabitants become modilied, the mutual relations 

 of others will often be disturbed; and this will create 

 new places, ready to be filled up by better adapted 

 forms; but all this will take place very slowly. Al- 

 though all the individuals of the same species dijEfer in 

 some slight degree from each other, it would often be 

 long before differences of the right nature in various 

 parts of the organization might occur. The result would 

 \yt)ften be greatly retarded by free intercrossing. Many 

 will exclaim that these several causes are amply suffi- 

 cient to 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, intermittent 

 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 com- 

 plexity of the coadaptations between all organic beings, 

 one with another and with their physical conditions of 

 life, which may have been effected in the long course 

 of time through nature's power of selection, that is by 

 the survival of the fittest. 



Extinction caused by Natural Selection 



This subject will be more fully discussed in our 

 chapter on Geology; but it must here be alluded to 

 from being intimately connected with natural selection. 

 Natural selection acts solely through the preservation of 



