On Hybrids

You may possibly recall that I was taking a class on Darwin(ism) this last spring, in which I learned that species are difficult things to pin down.  On one hand there is a clear idea of discreteness - lions are lions and tigers are tigers, that sort of thing - but on the other hand, there's a clear picture of individual differences - for us, this is best illustrated by looking at the great differences in our species, Homo sapiens.

Anyway.  One way to define what makes a species a species is to look into whether two individuals are able to generate viable, fertile, offspring.  This isn't as foolproof as it sounds, unfortunately (a large number of living organisms don't reproduce sexually at all; individuals may never produce viable offspring because of reasons other than genetic ones...they may live on opposite sides of an ocean, have different mating seasons, etc., but that doesn't mean they couldn't)...but it's a good starting point.  American bison and domesticated cows, for instance, have recently been reclassified into one genus, due to the fact that when mated, they produce a fertile breed - the beefalo. 

So what other species have interesting hybrids? 
There is, as mentioned above: cow x bison = beefalo
and everyone is most likely aware of horse x donkey = mule.
What might seem surprising is that the reciprocal cross, donkey x horse = hinny.
There are ligers and tiglons, respectively reciprocal crosses of lions and tigers.
As to bears, there are a number of hybrids that can occur between black, brown, and polar bears.
And don't forget the zebroids: zebra x donkey = zonkey
sebra x horse = zorse
and zebra x Shetland pony = zetland.
There's the Cama, camel x llama...
one of my favorites is probably the bottlenose dolphin x false killer whale = wholphin.

Of course, most of those are infertile or sterile hybrids, intergeneric or interfamilial crosses. 

Plants can crossbreed too, you know, with more success than animals.  There's the limequat (lime x kumquat) and the tangelo (mandarine orange x pomelo)...but I was definitely unaware - and surprised to discover - that peppermint, grapefruit, and even wheat are all apparently hybrid species.  Who could have guessed it?