Are there multiple species of humans?

A couple nights ago me and my lovely girlfriend were talking and we came around to a particularly interesting conversation. Are humans actually multiple different species? Part of the confusion comes in the fact that the definition of species is something that isnt universally agreed upon, but my understanding and definition is when one animal branches out and gets isolated from the others and takes on some sort of mutation changing its physical features or colors while still being very similar to whatever it branched off from. Based on this definition I would have to say yes there are many different species of humans. I mean sure we all started in africa, but as humans moved out and were isolated from the rest of the populations we all changed. You will never find someone from africa that looks like someone from asia or america. Bone structure, skin tone, hair, and many other things are completely different and unique to each.

Is race just a nice way of saying species without stepping on people toes? I mean I can see how racist people could really take something like this and run with it but from a strictly scientific standpoint im quite interested in the answer.

I also realize that now humans have completely covered the earth so everything just gets blended to a million shades of gray, but I would still think this to be even more different species or subspecies even. So….what say you fluther?