So you just found this out, when the show references it so much?still a great show though
I've heard of this theory a couple times before.even on the wikipedia page it talks about the show taking place in a post-apocalyptic era.
So I've come to the conclusion that Adventure Time is the aftermath of a nuclear war. They talk about how there is no humans (except for finn) and if you look closely there is some desert areas filled with ruined buildings, cars, etc. The human-like fish people living underground were probably decedents of survivors living underground in a fallout shelter. Years of living underground turned them into mutant fish people. *hyoomen sounds like human.As for the candy people, Radiation turned candy into living creatures. Radiation is also the cause for magic (such as Jake's powers).Also take a look at The Mushroom War.http://adventuretimewithfinnandjake.wikia.com/wiki/Mushroom_War img http://images2.wikia.nocookie.net/__cb20110519021419/adventuretimewithfinnandjake/images/e/ea/Vlcsnap2010060102h57m35.png /imgOpening shot of the theme song.