What a surprisingly interesting read. 
 There's plenty of food for thought, right from the announcement that Rosemary had her "Own personal Schrodinger's Cat," to her insistence that memories cannot be trusted. Even so, these minor reveals are not the important pieces that frame this narrative structure. They may be emotional and harrowing, but the novel is much more than just this. 
 It's really about our place in the universe and how "Others" fit within it, as well. 
 I was confused from the very start why this was nominated for a Nebula award, though not so much for why it was nominated for the Booker. The writing is very good and the number of topics and narrative juggling was as smooth as any I've seen. 
 There are no aliens in this tale. There are humans and apes. 
 I can't tell you how clever the afterthought works unless you read it yourself. Mind you, there aren't any twists. There are only after-effects. 
 This is a very psychological and sociological novel set up as a near-twin study and an attempt to obliterate social differences by simply raising both children the same at the same time, but instead of getting a well-ordered experiment, life happens. 
 In the end, though, I'm stuck in a quandary. 
 Is there any real difference between Rosemary's brother Lowell and Fern? Chimps or aliens, the question is entirely the same. Is it just to treat "Others" any different than we treat ourselves? And, obviously, shouldn't we be treating ourselves better? 
 These are the SF questions that I've seen a hundred times, and it's a real delight to see them brought so close to home. We can easily transfer Fern into our own brothers and sisters, or anyone who has mental illness, and see for ourselves just how poorly we treat our own. Imprisonment is imprisonment, no matter how you justify it or rename it. The whole idea falls into a fractal in this novel, applying itself to gender studies just as much as interspecies considerations, or even the episodic stories we tell ourselves to justify the things we've done. Memory is just as much a prison as anything. 
 Again: This novel was a real delight! :) 
 An easy read, too, believe it or not. :)