Reporters who get the chance to try to pry information out of Steven Moffat about the new companion debuting at Christmastime 2012 are having a devil of a time trying to get any worthwhile information out of the man.. Doctor Who Magazine could only get this:
"What is the base group of people who would run away with the Doctor? They're all going to be a bit mad. A bit dislocated. Not happy with where they are. Are they yearning for outer space? They're going to be people who feel like they can take on the Doctor, who's quite an intimidating sort of person. So, they're going to be feisty - they're going to be all those things. He sort of defines the people who are going to travel with him. The distinction comes very much from the various actors and actresses. So, you know, they’re the ones who create the differences between them. But you are always going to have the same sort of person, just because it's the same man choosing them, and it"s the same person being chosen."
When it comes to the gender of the Doctor's companions Moffat allowed, "I think the function of a companion is pretty simple. I don't think that's very difficult. It’s just a question of who credibly is going to agree to go in the TARDIS? Who’s going to do it? Is it going to be a mother of 15 children? No. Is it going to be someone in their 60s? No. Is there going to be a particular age range? I mean... who's going to have a crush on the Doctor? You know, come on! It's more than a format. It's evolved from good, dramatic reasons."
So, there you have it; only young, slightly mad girls need apply. I guess we should be glad Lindsey Lohan didn't land in the TARDIS only because she's completely nuts.