The DoctorDonna was an example of a human with a Time Lord consciousness. The Tenth Doctor stated that a human-Time lord metacrisis had never happened before, and that it was unsustainable. Donna had to be reverted to her human self; her brain could not hold a such a consciousness. The Doctor erased her mind of all knowledge of him. (TV: Journey's End) Despite this, Donna's latent consciousness retained at least some non-human aspects, protecting her when turned the world into copies of himself. Apparently, it also subconsciously guided her to buy a book for her grandfather, which led the Doctor and him to Joshua Naismith. (TV: The End of Time)