106 DARWINISM STATED BY DARWIN HIMSELF. 



or, more delicate and more easily broken shells might be 

 selected, the thickness of the shell being known to vary 

 like every other structure. 



ILLUSTRATIONS OF THE ACTION OF NATURAL SELECTION. 



ft . . - In order to make it clear how, as I believe, 



Origin or ' *■ 



Species, natural selection acts, I must beg permission 

 page 70. ^ Q g- ye one or £ wo imaginary illustrations. 

 Let us take the case of a wolf, which preys on various 

 animals, securing some by craft, some by strength, and 

 some by fleetness ; and let us suppose that the fleetest 

 prey, a deer for instance, had from any change in the 

 country increased in numbers, or that other prey had de- 

 creased in numbers, during that season of the year when 

 the wolf was hardest pressed for food. Under such cir- 

 cumstances the swiftest and slimmest wolves would have 

 the best chance of surviving, and so be preserved or se- 

 lected — provided always that they retained strength to 

 master their prey at this or some other period of the year, 

 when they were compelled to prey on other animals. I 

 can see no more reason to doubt that this would be the 

 result, than that man should be able to improve the fleet- 

 ness of his greyhounds by careful and methodical selec- 

 tion, or by that kind of unconscious selection which fol- 

 lows from each man trying to keep the best dogs without 

 any thought of modifying the breed. I may add that, 

 according to Mr. Pierce, there are two varieties of the 

 wolf inhabiting the Catskill Mountains in the United 

 States, one with a light greyhound-like form, which pur- 

 sues deer, and the other more bulky, with shorter legs, 

 which more frequently attacks the shepherd's flocks. 



