The Mule Outperforms Both Its Horse Mom and Donkey Dad

A mule is a cross between a male donkey (also known as a jack) and a female horse (called a mare). The result is a creature that inherits the best traits from both its parents. Humans have used mules for thousands of years because of their strength, stamina and resilience.

But what's really cool about mules is their unique status as a sterile hybrid. Because they're a combination of two different species, they can't reproduce, which adds another layer of intrigue to their biology.

Despite this, mules have a long history of usefulness in agriculture, transportation and even war.

The first recorded mules appeared in ancient civilizations, with evidence of their use dating back to at least 1000 B.C.E. in the Middle East. The modern word "mule" comes from Middle English, which, following the Anglo-French languages, modified the word "mulus" from the Latin.

Mules are sterile hybrids, meaning they inherit characteristics from both parents but are unable to reproduce.

This is due to the differences in the number of chromosomes between horses and donkeys. While horses have 64 chromosomes and donkeys have 62, mules end up with 63, which disrupts their reproductive capabilities.

There are also specific terms for different types of mules. A male mule is called a "john mule," and a female mule is known as a "molly mule."

But mules can only be born when a male donkey and a female horse mate; crossing a male horse with a female donkey results in a different hybrid called a hinny, which is rarer.

The hybrid vigor of mules means they often outperform both their horse and donkey parents in terms of strength and endurance, making them a valuable animal throughout history.

The mule inherits the body size of a horse but with the long ears of a donkey. Mules' coats and colors can vary widely, just like horses' and donkeys', but their heads are often a bit larger, more like a donkey's.

Thanks to their hybrid nature, mules have stronger muscle structures than donkeys, allowing them to comfortably carry relatively heavy loads for long distances.

Throughout their lives, mules are known for their hardiness and ability to thrive in tough conditions. Thanks to hybrid vigor, mules are often healthier and more resistant to disease than either horses or donkeys.

Despite their strength, mules are smaller than horses, making them a bit easier to handle. Their legs are more durable and less prone to injury than those of a horse, and their hooves are tougher: perfect for rocky or uneven terrain.

While you might be familiar with the old trope of "stubborn as a mule," the reality is that both the mule and the donkey are incredibly intelligent and cautious animals, which is often mistaken for stubbornness.

However, more so than donkeys, mules are known for their patience, sure-footedness and reliability — qualities that make them ideal for long journeys and hard work.

Mules inherit their longevity from both their donkey and horse parents, living an average of 30 to 40 years, with some even reaching 50 years old.

They grow quickly during their first few years of life and — like horses and donkeys — they go through a weaning period with their mother before becoming independent. Since mules are sterile hybrids, they don't reproduce, meaning every mule must come from a horse-donkey pairing.

While a mule can't pass on its traits to a new generation, its individual lifespan and ability to work throughout its life make it an incredibly valuable companion in agriculture, transportation and other labor-intensive roles.

In terms of survival in the wild, mules are highly capable. Their long ears and keen senses make them alert to predators, much like donkeys, while their horse-like endurance allows them to cover long distances without tiring.

However, because mules are sterile, they can't form wild populations on their own. In the wild, a solitary mule would have to join a herd of horses or donkeys to ensure protection and socialization.

While mules can fend for themselves, they thrive best in human-managed environments like farms or wilderness expeditions. Mules comfortably carry heavy loads across rough terrain, which is why they've been used for centuries in military campaigns, farming and long-distance travel.

Their adaptability in various environments has cemented their role in many cultures, particularly in the American West, where the American Donkey and Mule Society has kept their legacy alive [source: ADMS].

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.