| hoofed, herbivorous mammal now represented by a single extant genus, Equus. The term horse commonly refers only to the domestic Equus caballus and to the wild Przewalski's horse, E. przewalski. (Other so-called wild horses are feral domestic horses or their descendants.) Adapted to plains environments, all Equus species, including the ass and the zebra, have lengthened foot bones ending in a single toe covered by a hoof, for fast running; teeth shaped for grinding grass; and intestinal protozoa for digesting cellulose. All species have tufts of hair on the tail, used against insects, and manes on the neck. Horses, zebras, and asses can interbreed, but the offspring are usually sterile. The offspring of a horse and a donkey (domestic ass) is called a mule. A male horse is called a stallion, or if castrated, a gelding; a female is a mare; her offspring are foals—males are colts, females are fillies. A male parent is a sire, a female parent is a dam. A single foal is born after a gestation of about 11 months. Horses reach sexual maturity in about two years, but are not fully grown for about five years. The average life span is 18 years, but 30-year-old horses are common. The standard unit of height is a hand, equal to 4 in. (10 cm). See horse racing; equestrianism. History and Breeds The earliest known direct ancestor of Equus, the eohippus [Gr.,=dawn horse], 10 to 20 in. (25–50 cm) tall, lived approximately 50 million years ago in both the Old and New Worlds. Equus originally evolved in North America by the late Pliocene epoch, about three million years ago, spreading to all continents except Australia. Horses disappeared from the Americas for unknown reasons about 10,000 years ago, to be reintroduced by Europeans, c.a.d. 1500. Many species of Equus arose in the Old World. Horses were probably first domesticated by central Asian nomads in the 3d millennium b.c. Horses were recorded in Mesopotamia and China (c.2000 b.c.), Greece (c.1700 b.c.), Egypt (c.1600 b.c.), and India (c.1500 b.c.). Horses were domesticated in W Europe no later than 1000 b.c. It is not known whether these early domesticated horses developed from a single wild race or from many local races. Largely superseding the slower, less manageable ass, which had been domesticated much earlier, the horse's first known use was for drawing Mesopotamian war chariots. It was long reserved primarily for warfare and for transportation for the rich and well-born, while cheaper animals (e.g., oxen, mules, and donkeys) were used for lowlier work. Horses figured importantly in war and conquest in Europe, central Asia, and the Middle East for over 3,000 years. Early warriors rode bareback or with saddle cloths. The saddle and the stirrup were probably developed in China in the early Christian era, spread by Asian horsemen (such as the Huns), and adopted by Arabs and Europeans in the early Middle Ages. Arab cavalry conquered the Middle East and N Africa in the 7th cent. a.d. In the same period, armored knights were riding to battles in Europe. With highly developed cavalry tactics, the Mongols extended their 13th cent. empire from China to E Europe. The Spanish conquistadors brought horses to the New World, where Native Americans soon acquired them from ranches and missions. The Plains Indians of North America quickly developed a horse culture that led to their ascendancy in numbers and power. Horses were used for hunting buffalo and other game, for warfare, and for pulling loads on a travois. Escaped Indian horses were ancestral to the mustang, the so-called wild horse of the W United States. The two major groups of modern horses—the light, swift southern breeds, called light horses, and the heavy, powerful northern breeds, called draft horses—are believed to have arisen independently. The small breeds called ponies may derive from a southern, light horse or from a wild race. Draft Horses During Roman times the Gauls and other Europeans used horses of the heavy, northern type for pulling loads and other work. In the Middle Ages huge draft animals, over 16 hands (64 in./160 cm) high, were bred to carry armored knights as well as their own armor. As cavalry warfare declined, such medieval inventions as the horseshoe and the rigid horse-collar (see harness) made draft horses more useful for work. By the 19th cent. the draft horse had replaced the ox in N Europe and North America. Draft breeds common in the United States were the Belgian, the Clydesdale, the Percheron; and the Shire, also the most common draft horse in England. Light Horses Modern light horses, all descended in part from the Arabian horse, the oldest surviving breed of known lineage, include the Thoroughbred, celebrated as a racehorse; the American saddle horse, known for its easy gaits; the Morgan and the quarter horse, favored for riding and cow herding; and the Standardbred, or trotter, developed for light harness racing. The Appaloosa and the Pinto, much used in cow herding, are distinguished by their patterned colors. The palomino is not a breed but a color type. Among the small horses are the Shetland pony and Welsh pony. The terms cow pony and polo pony refer to the animal's use rather than its size or breed. Although little used for work today, horses are widely owned for recreational riding and show activities. Classification Horses are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Perissodactyla, family Equidae. Bibliography See A. Hyland, Equus (1990); E. H. Edwards and C. Geddes, ed., The Complete Horse Book (1991); K. R. Ward, The American Horse (1991); J. Clutton-Brock, Horse Power (1992); J. Holderness-Roddam, The New Complete Book of the Horse (1992). ____________________The Columbia Encyclopedia, Sixth Edition Copyright© 2004, Columbia University Press. Licensed from Lernout & Hauspie Speech Products N.V. All rights reserved. -22565- | 
