28 



EVOLUTION OF THE HORSE 



small one, in order to keep up a proper amount of activity. On 

 the other hand a large animal is better able than a small one to 

 defend itself against its enemies and rivals. Consequently, as 

 long as food is abundant, the larger animals have the advan- 

 tage over their smaller brethren, and by the laws of natural se- 

 lection the race tends to become continually larger until a limit 

 is reached, when sufficient food becomes difficult to obtain, the 



RESTORATION OF THE FOUR-TOED HORSE 



Oldest known Ancestor of the Modern Horse; only i6 inches high 



Photo from original watercolor by C. R. Knight, based on mounted skeleton in 



Am.erican Museum 



animal being compelled to devote nearly all its time to getting 

 enough to eat. 



Cause of the Evolution. 



The evolution of the Horse, adapting it to live on the dry 

 plains, probably went hand in hand with the evolution of the 

 plains themselves. At the commencement of the Age of Mam- 



