Then why not start with today and trace humans back to the original common ancestor above. Just remember there can be no gaps as when you get as far as you can go you are at a dead end.
So if you are only able to trace some line of your ancestry back to a great-grandfather, it means that his mom didn't exist? That great-grandpa was
created instead of born?
Barack Obama (and John McCain) and I share a common ancestor that came to Massachusetts in 1630, I think it was. But on my maternal grandmother's side, there's a "dead end" back in the middle 1800's. Does that mean I don't exist?