124 WILD TRAITS IN TAME ANIMALS. 



ance and a disposition to act independently of his 

 fellows would be most valuable in the struggle for 

 existence. 



How do we know that the donkey's ancestors 

 lived where pasture was scarce ? Because an ass 

 will eat a thistle ; showing that his mouth has 

 become adapted for such meagre and prickly diet 

 as is found in desert places. 



The dread of entering; running water is another 

 characteristic of the species. Darwin draws at- 

 tention to this as an indication that the domestic 

 ass first came from a region where water was 

 scarce. He also alludes to the delight all don- 

 keys show in rolling in the dust as an instance of 

 inherited desert habits. I cannot see why the 

 mere scarcity of brooks in the arid wastes of his 

 original home should give the beast this instinc- 

 tive aversion. One would think that, after a day 

 in the parched wilderness, the cool streams would 

 have been his delight. There evidently must 

 have been something about the Ethiopian rivers 

 which gave rise to well-founded emotions of fear. 

 What could it have been ? Crocodiles ? We 

 have seen how some horses become frantic with 

 terror at the rustle of reed-beds, because it was 

 at such spots that, for countless generations, some 



