However, for the purpose intended, he serves quite well. A mule is a sterile animal incapable of bearing offspring. The mule is a hybrid. The offspring of genetically different parents. In this case the cross of a horse and a donkey, produces a mule as the offspring.
Some people consider mules to be freaks.
But Hybrids occur in nature and far more often than you might think. Ask someone from Minnesota about hybrid fish. There are theories that some species were evolved from hybrids, especially in plants. When you prepare that delicious fresh corn you purchased at the market, it is almost a certainty that you are eating a hybrid, something that cannot reproduce itself naturally. To achieve results that cannot be had from the offspring of genetically identical parents, folks who work with mules will tell you very quickly, that mules are more intelligent than horses or donkeys.