NATURAL SELECTION 



two moths have just the same length of pro- 

 boscis, no two antelopes are exactly matched in 

 fleetness. Now if increasing cold renders a 

 thicker covering useful to the bear, or if the 

 lengthening of a flower-calyx, due to a slight 

 change in soil or quantity of sunlight, renders a 

 longer proboscis useful to the moth, or if the 

 immigration of a carnivorous animal makes it ne- 

 cessary for antelopes often to run for their lives, 

 then in each generation the thickest - coated 

 bears, the longest-tongued moths, and the fleet- 

 est antelopes will survive. Every individual 

 variation in the direction of a heavier coat, a 

 longer sucker, or a structure better adapted for 

 fleeing will give its owner the advantage in the 

 incessant struggle for life, and these peculiari- 

 ties will be oftenest inherited, while individuals 

 which do not vary, or which vary in tue wrong 

 direction, will have to migrate or die.^ 



The student of natural history, who realizes, 

 however dimly, the prodigious complexity of 

 the relations of the various species of animals 

 and plants to each other, will perceive that the 

 amount of variation thus preserved and en- 

 hanced must in the course of long ages become 



1 It is thus one of the great merits of the theory of natural 

 selection, that it accounts for the phenomena o^ extinction of 

 species, — which formerly could only be accounted for by 

 the gratuitous and utterly indefensible hypothesis of periodical 

 catastrophes or cataclysms. 



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