154 ANIMALS OF THE PAST 



climate with their accompanying variations in 

 the supply of food, and, to a lesser extent, 

 against their various enemies, including man. 

 This power of flight, acquired early in their 

 geological history, has enabled birds to spread 

 over the length and breadth of the globe as no 

 other group of animals has done, and to thrive 

 under the most varying conditions, and it 

 would seem that if this power were lost it 

 must sooner or later work harm. Now to-day 

 we find no great wingless birds in thickly 

 populated regions, or where beasts of prey 

 abound ; the ostriches roam the desert wastes 

 of Arabia, Africa and South America where 

 men are few and savage beasts scarce, and 

 against these is placed a fleetness of foot inher- 

 ited from ancestors who acquired it before 

 man was. The heavy cassowaries dwell in the 

 thinly inhabited, thickly wooded islands of 

 Malaysia, where again there are no large carni- 

 vores and where the dense vegetation is some 

 safeguard against man ; the emu comes from 

 the Australian plains, where also there are no 

 four-footed enemies * and where his ancestors 



* The dingo, or native dog, is not forgotten, but, like man, 

 it w a comparatively recent animal. 



