Natalie Portman bails on Cuaron, so he gets the most similar actress possible.

Sandra Bullock to Replace Natalie Portman in Space Film

Ok, so they wanted somebody who was 20-something, beautiful, aloof, intellectual, and unsmiling, the kind of woman who would slap a restraining order on you if you tried to talk to her without making an appointment. When they couldn't get her they settled for a friendly, down-to-earth, highly approachable, always smiling, comedienne in her mid 40s.

Well, you see they are both beautiful and they both have vaginas!

Although, to be fair about that vagina and beauty thing, they originally turned to Tom Arnold when Portman bailed.