Okay, so the idea was something to the extent that there was a WWIII (World War III), that resulted in a nuclear apocalypse. There was some warning before it happened, so the wealthy people and their family paid to have them transported underground to safety, but the others weren't as fortunate, as they had to struggle to survive on the outside in radioactive warzones. Most of the humans (and animals) on the outside were wiped out, but there were a few survivers, though mutated.
The ones underground lived out safely and had all the supplies they needed for survival for a millenium, and eventually began to evolve over time, adapting to their sunless, mechanic environment. Their eyes became larger, senses lowered, bodily functions slowed, they lost the hair on their bodies and heads, their legs became shrunken and useless, and arms and fingers elongated due to centuries of typing (they live practically on computers their entire lives), and lost most of their language. For now, I'll call them "Techies."
"Earthies," on the other hand, also evolved past mutations and became relatively humanoid again (there are still some born with, say, an extra limb from time to time). At about this time, life is resuming its course and there are plants and animals to eat and all that. The Earthies, for the most part, are the complete opposite of Techies; They survive in the harsh outside world, are taller, have longer and wider feet for stability, dark skin, narrow eyes, durable hands, and larger muscles. The women almost always have multiple children at once, as most people don't live past their thirties.
Anyway, the thing that moves the plot along is this:
A Techie man has the idea to start an experiment. He builds a robot and sends it up into the light, and it comes across an Earthie female foraging for herbs and berries. The robot injects her with a sedate and takes her back. While she is still unconcious, the Techie man injects her with another vial, then puts her back where she was. She wakes up and thinks it was all a strange dream.
9 months later: The woman has one child (can't decide on boy or girl). The child is a half-breed, though inherited more Earthie traits than Techie. However, the child is still outcasted and sent away to live in exile.
One day, the child, now a little older, finds itself in a ruined home and runs into the basement, looking for shelter from the severe weather. It knocks over something in the dark, and a television turns on. It's a documentary of the apocalypse (the child can't understand the language, but still has a basic grasp on the meaning). The child decides to find out all it could about the apocalypse and life before it.
And now...I can't tell the ending, and it might change anyhow. So please tell me what you think, and if you have any suggestions, please tell!
And also, don't steal my idea. I will cut you.