Mules are a Hybrid of a Donkey and a Horse

One aspect of selective breeding is the creation of hybrids. In the animal world, a hybrid can usually not reproduce. Mules are a hybrid between a horse and a donkey and while they cannot reproduce, they make a sturdy and reliable pack animal. teachingscience.us/selective-...
Sometimes the production of a hybrid has a negative effect. Ligers, a cross between a tiger and a lion, often have enlarged hearts. Ethical questions in producing hybrids need to be considered. Just because we can, should we?