While mules are overwhelmingly sterile, I thought it was neat to learn that there are instances of fertile female mules, though no male ones are on record as having been fertile.
With fertile female individuals I'm amazed (would be amazed if?) people haven't made an effort to breed and maintain animals right along the spectrum (or at least one half of it.)
There are only 60 known instances of fertile female mules in the last 500 years, according to Wikipedia, and they don't breed true - their offspring appear phenotypically to be pure donkeys or pure horses.
