The horse is one of the world's fastest land animals. A galloping horse can top 40 miles (64 kilometers) per hour--a breathless pace compared to a person running on foot. Perhaps it's not surprising, then, that almost everywhere horses are found, people love putting their speed to the test.The finest racehorses have long legs and powerful muscles. These traits first evolved in the wild, where horses had to move fast to flee predators and travel far to find food. Eventually, horse breeders chose some of the longest, leanest horses to develop racing breeds that are especially sleek, slender, and swift.

Bronze statue of Lee Axworthy, 1925, by Amory Coffin Simons.

Denis Finnin/AMNH

Standardbred Trotter

Some horses are bred to race at a fast trot instead of a gallop, while pulling a driver in a lightweight cart called a sulky. A champion trotter, known as Lee Axworthy, was the first horse in racing history to trot a mile (1.6 kilometers) in less than two minutes. His skeleton shows the long, low lines of a typical American standardbred, the fastest of all trotting breeds.Standardbreds are descended from thoroughbred racehorses and have a similar lean build, but with shorter legs and heavier bones. In the 1800s, breeders selected horses that could trot or pace a mile (1.6 kilometers) within the "standard" time of 2 minutes to develop the breed.

How Fast Was This Horse?

In a harness race against the clock, the standardbred racehorse Lee Axworthy trotted a mile (1.6 kilometers) in one minute, 58; seconds, for an average speed of just over 30 miles per hour. An ordinary horse gallops at about the same speed.

What Makes a Great Racehorse?

By taking bone samples from skeletons, scientists in Great Britain are studying the DNA of successful thoroughbreds, including the champion racehorse Eclipse, pictured here. Born in 1764, this sensational stallion never lost a race. But most researchers agree that genetics are just a small part of what makes a champion. The environment in which a horse is raised, its food, training, and the jockey who rides it can make all the difference in its success.

Founding Fathers

The most illustrious racehorses in sports today are thoroughbreds--strong, long-legged, sensitive animals famed for their beauty as well as their speed. Thoroughbred horses are bred to carry a jockey and race at a gallop. The breed was founded in England in the 1700s, after three legendary stallions were brought to Europe from North Africa and the Near East. All thoroughbreds--winners and losers--are descended from these "foundation sires." They are known as the Darley Arabian, Godolphin Barb, and Byerley Turk.