Do wild animals ever cross breed, even across species?
Aside from a few musicians that I have known: There are many modern examples of hybridization in nature, some forced, some natural. Mules are bred by humans from horses and donkeys, are completely sterile, and represent an evolutionary dead-end. But there are other species-crossings that do just fine, such as offspring of the notoriously promiscuous oak tree species, which hybridize so often species-namers commonly joke about not being able to keep up. Still, cross-species matings usually result in sickness or sterility, if the offspring get that far –many naturally abort. Hybrid offspring that are fertile but sick or weak will not be able to compete with the purer offspring of either parent in passing on their genes to future generations. As a result, many evolutionary biologists have thought hybridization to be evolutionarily unimportant.
