CH. X.] NATURAL SELECTION. 19 



powerful of tliese would find manifest advantage in crouching 

 amid dense foliage and springing down upon imwary victims 

 passing below. The larger and more powerful individuals 

 would more frequently roam about the open country, attack- 

 ing the larger ruminants and giving chase to the nimbler 

 ones, and would thus increase in strength and fleetness. 

 And thus there would be initiated such differences of size 

 and habit as characterize the leopard and the lion. 



It must be borne in mind that this is a purely hypothe- 

 tical illustration, which does not pretend to give a complete 

 account of the complex process. I have no idea that the 

 differentiation between antelopes and buffaloes, or between 

 lions and leopards, was accomplished in any such straight- 

 forward way as this. But while unduly simplifying the 

 case, the ilhistration is undoubtedly sound in principle. No 

 doubt the lion is so strong and so swift because only the 

 strongest and swiftest lions have been able to prey at once 

 upon buffaloes and upon antelopes. No doubt the antelope 

 is so swift and so timid because only the swiftest and most 

 quickly-frightened antelopes have been enabled to get away 

 from the lion, and to propagate their kind. And no doubt in 

 the nrocess above described, we get a partial glimpse of some 

 of the essential incidents in the past careers of these races. 



All the foregoing illustrations unite in enforcing the con- 

 clusion that the direct and indirect effects of natural selection 

 are by no means limited to slight or superficial changes iu 

 organisms. The student of physiology well knows that no 

 change, however seemingly trivial, which ensures the sur- 

 vival of the organism in its fierce struggle for existence, can 

 fail in the long 'run to entail so many other changes as to 

 modify, more or less perceptibly, the entire structure. Even 

 such a slight change as an increased thickness of the woolly 

 coat of a mammal may, by altering the excretory power of 

 the skin, affect the functions of the lungs, liver, and kidneys, 

 and thus indirectly increase or diminish the size of the 



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