But the Doctor doesnt have a monopoly on affecting human history. Doctor Who is an equal opportunity meddler when it comes to established events, so the various aliens of the universe get their chance to screw around with history as well. Whenever something odd happens, its usually because of aliens. The Cybermen accidentally wiped out the dinosaurs. The moon landing was orchestrated by the Silence. And of course, Jack The Ripper was never officially caught because Vastra got there before the police and ate him. But then again, it's kind of fitting that aliens have ended up shaping Earths history so much when you consider that the planet only exists because theres a spaceship full of giant spider monsters at the centre of it. Why humans owe so much of their history to aliens (yet still take thousands of years to realise they exist) is anyones guess but like the Doctor affecting history, its one of those things that has become such a big part of Doctor Whos DNA that its best to just lay back and accept it. But not to think about the Racnoss at the centre of the Earth if youre an arachnophobe.