Consider the idea of spontaneous genesis of life, as used to be belived. What strange kinds of life might arise from modern substances? What kind of vermin would a landfill produce, or an oil spill on the ocean?
A demon who isn't some hideous creature bent on consuming souls, bu is, in fact, a likable chap who enjoys having pleasant chats with people - trying to talk them into becoming his servants.
(Post zombie apocalypse)-a tribe of humans
Culture: Drumming circles daily around an arena for their bravest brutes to slaughter their accepted foe, the zombie. Feasts of overcooked zombie flesh (to kill all of the zombie virus present). Wooden fortress that make this tribe in the far future look several millennium behind in technology. Instead of becoming a troublesome and unnatural foe that they seek to cure, this tribe has accepted that Zombies will continue to roam their land and, if the undead were to perish (be cured), this tribe would suffer as well.