316 THE VERTEBRATE ANIMALS 



numbers on our Western plains. They were hunted by whites 

 and Indians for the hides and tongues only, and thousands of 

 carcasses were left to rot after a hunt. They are now almost 

 extinct. 



Geologic History of the Horse. In some ungulates the middle 

 toe of the foot has become largely developed, with the result that 

 the animal stands on it. Such are the zebra and the horse. 



We have, from time to time, made reference to the fact 

 that certain forms of life, now almost extinct, flourished on 

 the earth in former geologic periods. It is interesting to note 

 that America was the original home of the horse, although at the 

 time of the earliest explorers the horse was unknown here, the 

 wild horse of the Western plains having arisen from horses 

 introduced by the Spaniards. Long ages ago, the first ances- 

 tors of the horse were probably little animals about the size 

 of a fox. The earliest horse we have knowledge of had four toes 

 on the fore and three toes on the hind feet. Thousands of years 

 later we find a larger horse, the size of a sheep, with a three-toed 

 foot. By gradual changes, caused by the tendency of the animals 

 to vary and by the action of the surroundings upon the animal 

 in preserving these variations, there was eventually produced our 

 present horse, an animal with legs adapted for rapid locomotion, 

 with feet particularly fitted for the life in open fields, and with 

 teeth which serve well to seize and grind herbage. 



Domestication of Animals; Breeding by Selection. The 

 horse, which for some reason disappeared in this country, con- 

 tinued to exist in Europe, and man, emerging from his early savage 

 condition, began to make use of the animal. We know the horse 

 was domesticated in early Biblical times, and that he soon became 

 one of man's most valued servants. In more recent times, man 

 has begun to artificially change the horse by breeding for certain 

 desired characteristics. 



To do this, the horses which have varied so as to show the char- 

 acters desired by the breeder are selected and bred together. The 

 young from these animals are likely to be like the parents and, be- 

 cause of the tendency of animals to vary, will be even more likely 

 to show the characters the breeder desires than their parents. If 

 this process is repeated for several generations, it will be seen that 



