Boy, you're gonna have to ask someone who knows a lot more about than me! . . . But I'm assuming they "know" from the fossil record and the DNA trail. However, see x1stcav's comment. I saw something about that, too, and am trying to track it down.
Thank you. My intentions were not to put you in a spot. I apologize. My question was out of order. It should have been a general question to "all."
My best regards.
National Geographic is currently conducting research on this and has invited the public to participate. You have to pay for the DNA kit. I signed up and am waiting to hear something.
They also have an interactive map on their site which is interesting and shows the common theory of ancient humans migrating to Europe and parts of Asia, then Siberia to North America, etc.
I have not heard of the possibility of debunking a common ancestor but if anyone is researching this, I'd like to know more.