The wild ancestors of the modern horse evolved for millions of years in North America. They spread to other parts of the world by traveling southward to South America and by crossing land bridges that connected North America to Europe and Asia during the ice age. Horses vanished from both North and South America in a wave of extinctions that occurred near the end of the Pleistocene Epoch, about 15,000 years ago. They were not seen in the Americas again until 1494, when Italian explorer Christopher Columbus transported them on ships from Spain on his second voyage to the New World.
Przewalski 's horse, which is believed to be the only truly wild horse to survive to modern times, probably became extinct in the wild in Mongolia in the 1960s. About 1,100 Przewalski 's horses survive today in captivity in zoos and wildlife parks.
II PHYSICAL CHARACTERISTICS
As a result of deliberate breeding by humans, horses display a remarkable variation in size, body shape, and coat color. Traditionally, a horse's size is measured at the withers-an elevated part of the spine between the neck and the back. The measurement is made in hands; one hand equals about 10 cm (4 in). Typical riding horses stand 14 to 16 hands high and weigh 400 to 500 kg (900 to 1,100 lb). The smallest horse on record, a Falabella miniature pony, stood 48 cm (19 in), or just under 5 hands, and weighed 14 kg (30 lb). The largest horse on record was a Belgian that stood 1.8 m (6 ft) tall, or 18 hands, and weighed 1,450 kg (3,200 lb).
The horse has a hairy coat and a long mane and tail. A heavy winter coat grows in the fall and sheds in the spring. Typical coat colors include black, brown, gray, cream, gold, and white. The mane and tail can be the same or different from the body color, and many variations in color can result from inherited traits that cause spotting, dilution of the basic coat colors, or a sprinkling of white hairs in the coat.
