Worthy of note: Orson Scott Card's first book, "A Planet Called Treason" (1979), is about a planet where scientists were exiled generations ago and now the tribes that descended from them exchange their know-how or skill with "terminals" that provide iron (an element missing from the planet). The protagonist, Lanik Mueller, comes from a tribe that heals from wounds nearly immediately but occasional genetic abnormalities lead to freaks that grow multiple arms, legs, noses, etc. with the Mueller clan cuts off and feeds to the terminal. As science fiction, it's one of the most imaginative settings I've ever encountered and it was still early days so Card doesn't smother you with his Mormon iconography (although it still has a messiah-complex in the middle and forward progress cannot be made without massive destruction, as per usual Card). Then of course he retconned it like ten years later into another book altogether and added a bunch of tedious shit.