If every animal species lined up for a marathon, which one would actually win?

If we look at a marathon—a distance of 26.2 miles—the winner depends on the environment, but the undisputed champion in the animal kingdom is the human.

While many animals are much faster in a sprint, humans are among the best "persistence hunters" on the planet. Our ability to sweat and our bipedal efficiency allow us to regulate our body temperature and maintain a steady, grueling pace over long distances that would cause most other animals to overheat and collapse.

However, if the race were held in a specific environment, the results change:

• In extreme heat: Humans are the favorites. A fit human can outrun almost any mammal over a long distance on a hot day because we don't have to stop to pant or rest to shed heat.
• In temperate climates: Horses are fierce competitors. A horse can maintain a galloping speed that far exceeds a human's marathon pace. In the annual "Man versus Horse Marathon" in Wales, which covers 22 miles of hilly terrain, the horses have won the vast majority of the races since the event began in 1980.
• For pure endurance: If the marathon were extended to an ultramarathon (100 miles or more), the pronghorn antelope or the camel would likely take the lead. Camels are biologically built to cover immense distances across deserts with minimal water, and pronghorns have evolved to maintain a high aerobic capacity over very long stretches.

In short: If you want to win a standard marathon on a hot day, bet on the human. If you want to win a long-distance race across rugged, varied terrain, bet on the horse.