The New York Times reported on a 2007 paper in the journal Sports Medicine. "Daniel E. Lieberman, a Harvard evolutionary biologist, and Dennis M. Bramble, a biologist at the University of Utah, wrote that several characteristics unique to humans suggested endurance running played an important role in our evolution.
Most mammals can sprint faster than humans having four legs gives them the advantage. But when it comes to long distances, humans can outrun almost any animal. Because we cool by sweating rather than panting, we can stay cool at speeds and distances that would overheat other animals. On a hot day, the two scientists wrote, a human could even outrun a horse in a 26.2-mile marathon."
What was really fast about the Pony Express
The legendary Pony Express was a service delivering messages, newspapers, and mail using relays of horse-mounted riders between Missouri and California. The horse and riders (mostly the horse) carried pouches with twenty pounds of mail.
In 1872, Mark Twain waxed poetic in his book "Roughing It" about a Pony Express rider and his horse: "He rode a splendid horse that was born for a racer and fed and lodged like a gentleman; kept him at his utmost speed for ten miles, and then, as he came crashing up to the station where stood two men holding fast a fresh, impatient steed, the transfer of rider and mail-bag was made in the twinkling of an eye, and away flew the eager pair and were out of sight before the spectator could get hardly the ghost of a look."
The Pony Express was faster than the alternative. The 2,812 mile stagecoach route from Tipton, Missouri, to San Francisco, California, that took 25 days, the Butterfield Overland Mail stagecoach traveled about 110 miles a day, averaging roughly four and a half miles per hour.
Less well remembered is the great speed in which the Pony Express went bankrupt. It operated from April 3, 1860, to October 26, 1861, closing the stable door in just 19 months. I doubt there are many businesses that have had such a short actual history and have lived on as long in history.
Comparing the speed of horses and humans
The Pony Express was set up to provide a fresh horse every 10-15 miles and a fresh rider every 75-100 miles. 75 horses were needed total to make a one-way trip. Average speed was 10 miles per hour.
Ten runners have run marathons faster than 2:03:13. That's averaging 12.76 miles per hour or faster for the 26.2 mile race.
Perhaps a more equitable and contemporary comparison between horse and human happened 2010. On March 20 of that year Yousuf Ahmad Al Beloushi (not to be confused with brothers John and Jim) and an 11-year-old grey gelding rode 100 miles in 5:45:44. Yousuf averaged 17 mph during the ride and in the final loop averaged 22 mph. The Chronicle of the Horse Apparently it wasn't a hot day.