120 ORIGIN OF SPECIES 



create new places, ready to be filled up by better adapted 

 forms ; but all this will take place very slowly. Although all 

 the individuals of the same species differ in some slight de- 

 gree from each other, it would often be long before differ- 

 ences of the right nature in various parts of the organisation 

 might occur. The result would often be greatly retarded by 

 free intercrossing. Many will exclaim that these several 

 causes are amply sufficient to neutralise the power of nat- 

 ural 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 complexity of the co- 

 adaptations 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 NATURAL SELECTION 



This subject will be more fully discussed in our chapter on 

 Geology; but it must here be alluded to from being inti- 

 mately connected with natural selection. Natural selection 

 acts solely through the preservation of variations in some 

 way advantageous, which consequently endure. 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 favoured forms increase in 

 number, so, generally, will the less favoured decrease and 

 become rare. Rarity, 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 extinc- 

 tion, during great fluctuations in the nature of 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 pro- 

 duced, unless we admit that specific forms can go on indefi- 



