ID This 1950's SCiFi Story?

I can’t remember the author or title, but I do remember the basic plot:
it was about a young man who lived on a giant, interstellar spaceship. The ship was so huge that it was devided into “evels”-and the “lower” levels (ghetto?) were inhabited by degeneate humans (muties).
There was also a two-headed human (Joe’Jim) in the story.
Anybody know what the story was? Idon’t remember much more.

“Universe” and “Common Sense” by Robert Heinlein; they were published together in a book called “Orphans of the Sky”

And just to nitpick, it was the higher levels (closer to the radiation from the Converter, and with less gravity) where the muties lived, not the lower levels.

This is how prophetic Heinlein was.

Thanks-the book (apparently) is not available at my local library.
I guess i’ll have to buy it.