I was expecting them to be sterile as well, @strongerbeings, so I was also surprised when I found out that you can actually breed them.

Haha, that's a funny story. I would not want to see the results of four children fighting a liger, a lion or a tiger! That would not end so well :P

Yeah, it is really something to think about. It requires pretty extensive genetic tests to figure out the origin for a certain species, so I'm sure there are more hybrid species on the planet, that we just haven't figured out yet.