IN-BREEDING PREVENTED BY NATURE. 363 



ground of the bison, lessen many an overgrown herd, 

 and give rise to fresh ones, formed in many cases no 

 doubt from the waifs and strays of several old ones. 

 What happened to the Red Indian himself was but an 

 example of what happened to his friend the bison too. 

 But Nature had other and more stringent means by 

 which to enforce her laws, and to re-invigorate with 

 fresh blood her creatures. The grand means was to 

 make them what the sportsman calls pack — thousands 

 of herds united into one for an annual or semi-annual 

 emigration. The necessities of living required them to 

 travel so united for thousands of miles ; who can doubt 

 that many a herd would be reduced to its elements and 

 re-constituted in the process ? How much more would 

 this be the case when one of those great stampedoes 

 occurred to which wild cattle are from various causes 

 subject, and which have been described by travellers as 

 so sublimely awful ? Then, impelled by fear, perhaps 

 urged on by pursuing flames, the teeming millions rush 

 they know not where, down precipices, through rivers — 

 drowned, destroyed, trampled on — yet ever rushing on 

 over the bodies of their slaughtered fellows. Surely 

 we need not dream of the sire, dam, sons, and daughters 

 coming together again to continue their in-and-in breed- 

 ing after such wholesale destruction as that. Nature 

 herself, by one of the grandest of her convulsions, has 

 interfered to stay the evil, and has provided them with 

 mates of a different strain of blood. Nor in many cases 

 are the attacks of man and carnivorous animals without 

 some effect. They decimate the herds, and compel them 

 to unite, as the lessened coveys of grouse and partridge 

 do, for greater protection against the hunter. 



It appears from Azara, as quoted above by Darwin, 



