Different dog types are not different species. They are different RACES within the species. Two of any type dog mated together produces viable offspring that can reproduce. This is even applicable to wolves and dogs. I have read that the DNA of a wolf and chihuahua are virtually identical, proving that all dogs are really domesticated wolves.......
I have read that the DNA of a man and a monkey are virtually identical, proving that all men are really ...
A "species" is defined as a a group that can naturally breed and produce viable offspring (that can itself breed).
Mastiffs and Chijuaja(sp?) cannot naturally breed. Ergo, although they had a common ancestor just a few hundred years ago, they no are no longer the same species.
And no, artificial insemination does not count.
If so, lions and tigers would be the same specifies (the resulting offspring is called a Liger, which do exist, albeit they are generally sterile like a mule, which is itself an inter-species cross ).
In fact, HUMANS and CHIMPS can be bred together via artificial insemination. The Chinese did this, impregnating female chimps with human sperm. Fortunately, the resulting creature was destroyed before term (or so the Chinese claim).
So many breeds have been "created" by man for specific traits such as size, coat, skills, etc., I don't think this research means much. Additionally, the cultivation of certain traits also (inadvertently) has led to other problems within breeds, such as susceptibility to certain afflictions, etc.
I knew there was a reason I didn't trust the little rats.
You're absolutely right- the only time I've been bitten by a dog- it was a little rugrat!!