Right, I'm well aware that this issue has most likely been discussed many times over by now, but sod it, I'm gonna start it again. Do the events of "Journey's End" with the half-human Meta-Crisis Doctor invalidate the idea that the character could ever have been half-human? It's been a while since I last watched it, but I'm pretty sure it was said that a human/Time Lord hybrid was something that had never happened before, and that such hybrids would only have one heart and be unable to regenerate. I did at one time seriously consider the idea that the Seventh Doctor had at some point prior to his regeneration incorporated some human DNA into himself for some reason, but then I realised that any such human material would have been erased when he regenerated. And as already noted, "Journey's End" states there were no such mergings prior to the Meta-Crisis.