8 THE CHANGING CLIMATE 



and desert each claim one-third of the land 

 surface. We are passing on to the phase, 

 which Mars has reached, of world-wide desert, 

 and beyond that is the far future when, like 

 the Moon, our Earth will swing dead through 

 the great deeps of space. 



As the slow tremendous change of the 

 Earth's climate narrowed the forest, there 

 was no longer food for all the woodland 

 animals, and some of them ventured out into 

 the open glades. Here was a final parting of 

 the wa3's between the tapir who stayed in the 

 woods and the horse-ancestor w^ho went out 

 into the open. He was as yet no bigger than 

 a sheep, and still wore three toes on each foot, 

 but the grass diet agreed with him, for his 

 tribe soon grew to the size of an EngHsh 

 donkey. The firmer ground no longer needed 

 a wide tread to the foot. Slowly the second 

 and fourth toes shrank away up the leg, and 

 hung there like the dew claw of a dog, some- 

 times surviving more or less even in human 

 times, as with Juhus Caesar's charger. The 

 next ages evolved an animal the size of our 

 ponies, running on one toe hardened to the 

 hoof we know to-day. The snout diminished, 

 while the tail became a fly whisk. 



So we have the beginning of a group of 



