Horses are all members of a family of animals called equids.Equids also include zebras and donkeys (also known as asses).The first member of the equid family was the dawn horse，or eohippus.Eohippus was the ancestor of all modern horses，zebras，and donkeys.
Eohippus roamed North American forests about 55million years ago.Eohippus was a lot smaller than a modern horse and had four toes on its front feet and three toes on its rear feet.Modern horses have only one toe on each foot.
About 20million years ago，there were many kinds of equids in North America.These wild equids spread to other parts of the world.They crossed land bridges that connected North America to Europe and Asia during ice ages.
How Did People Tame Horses？
人是怎样驯化马的？
About 7，000years ago，people living in the grasslands of Asia learned to tame the wild horses that lived there.Herds of tamed horses grew.They were sold to people all over Europe.
Today，there are about 60million tamed horses living throughout the world.There are only a few wild horses left.These horses are descended from tamed horses that escaped or were turned loose.
How Do People Use Horses？