1494: THE STORY OF THE UNIVERSE 



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 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 in- 

 habiting 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 frequently attacks the shepherd's flocks. 

 To the effects of intercrossing in eliminating va- 

 riations of all kinds, I shall have to recur; but it may 

 be here remarked that most animals and plants keep 

 to their proper homes, and do not needlessly wander 

 about; we see this even with migratory birds, which 

 almost always return to the same spot. Consequently 

 each newly formed variety would generally be at 

 first local, as seems to be the common rule with va- 

 rieties in a state of nature; so that similarly modified 

 individuals would soon exist in a small body together, 

 and would often breed together. If the new variety 

 were successful in its battle for life, it would slowly 

 spread from a central district, competing with and 



