Mule

In its common modern meaning, a Mule is the offspring of a male donkey and a female horse.

Mules (males) are always sterile. The sterility is attributed to the different number of chromosomes the two species have: donkeys have 62 chromosomes, while horses have 64. Their offspring thus have 63 chromosomes, which cannot evenly divide. A female mule, called a "molly," has a regular period of sexual excitement during which she seeks to mate and can carry a fetus, as has occasionally happened naturally but also through embryo transfer. The difficulty is in getting the molly pregnant in the first place.

In its short thick head, long ears, thin limbs, small narrow hooves, short mane, absence of chestnuts (horny growths) inside the hocks, and tail hairless at the root, the mule appears weird in form. In height and body, shape of neck and croup, uniformity of coat, and teeth, it resembles a horse. In addition, characteristic of the mule is its enormous phallus, hence the popular colloquial expression. The mule has the voice neither of the donkey nor of the horse, but emits a feeble hoarse noise. Most mules have a brown or bay-brown coat: a chestnut tint sometimes appears.

The mule possesses the sobriety, patience, endurance and sure-footedness of the ass, and the vigor, strength and courage of the horse. Operators of working animals generally find mules preferable to horses: mules show less impatience under the pressure of heavy weights, as their skin is harder and less sensitive than that of horses.

Humans have used mules from early times; the inhabitants of Mysia and Paphlagonia allegedly bred the first mules. The ancient Greeks and especially Romans valued mules for transport, employing them to draw carriages and carry loads. In the 19th century, mules hauled barges on the Erie Canal and other North American and European canals, and teamsters on the U.S. Western frontier often used mule teams. In the early 20th century, use of mules survived mainly in military transport, used to haul artillery through nearly impassable terrain, the bravery and focused intelligence of the animal serving it well in the midst of the noise and confusion of warfare. Mules have become far less common since the rise of the automobile, the motorized tractor, and other internal combustion-powered vehicles. They still find employment in less-developed countries, and in certain specialized roles for which they are aptly suited. Mules can negotiate well on narrow, steep trails. Mules (and burros) can handle extremely rugged terrain and tracks that are too steep and twisted for the less sure-footed horse or for a motor vehicle.

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