Chap. IV.] NATURAL SELECTION, m 



for food. Under such circumstances the swiftest and 

 slimmest wolves would have the best chance of surviving 

 and so be preserved or selected,— 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 fleetness of his greyhounds 

 by careful and methodical selection, or by that kind of 

 unconscious selection which follows 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 pursues deer, and the 

 other more bulky, with shorter legs, which more fre- 

 quently attacks the shepherd's flocks. 



It should be observed that, in the above illustration, 

 I speak of the slimmest individual wolves, and not of any 

 single strongly-marked variation having been preserved. 

 In former editions of this work I sometimes spoke as if 

 this latter alternative had frequently occurred. I saw 

 the great importance of individual differences, and this 

 led me fully to discuss the results of unconscious se- 

 lection by man, which depends on the preservation of all 

 the more or less valuable individuals, and on the de- 

 struction of the worst. I saw, also, that the preserva- 

 tion in a state of nature of any occasional deviation of 

 structure, such as a monstrosity, would be a rare event; 

 and that, if at first preserved, it would generally be lost 

 by subsequent intercrossing with ordinary individuals. 

 Nevertheless, until reading an able and valuable article 

 in the ' North British Review ' (1867), I did not ap- 



