....or, put another way, the scientific definition of what constitutes a seperate "species" is rather arbitrary, and based mostly on things like minor differences in skeletons, etc. It has nothing to do with whether the two "species" can interbreed with each other, or not. Obviously, if two groups can't interbreed, they are two seperate species; but the reverse is NOT true: ability to interbreed does not automatically make the two groups part of the same species.
One could just as easily define the different "races" of humanity as different "species"; it is an arbitrary term, the definition of which depends entirely on the assumptions and definitions that one starts out with in the first place. That's why evolutionary physchology is a more useful discipline for understanding the differences between human populations, because it takes into account the behaviours and group strategies that differentiate different human evolutionary groups, rather than obsessing over just the bare physical differnences between groups.
One other possibility as I see it: it doesn't strike me as terribly far fetched that the biblical descriptions of Adam and Eve as the first humans might have meant "first such as us", as opposed to neanderthals.