THE SKELETONS ARE CORPSES (AN UNDERTALE THEORY)

SKELETONS ARE SHOWN AS AN UNNATURAL SPECIES, AS THERE ARE NO OTHER SKELETON MONSTERS IN THE GAME BESIDES THE SKELETON BROTHERS THEMSELVES. AND BECAUSE OF HOW UNNATURAL THEY ARE, AND USING SOME STANDPOINTS I HAVE GOTTEN ABOUT THEIR POSSIBLE ORIGIN, THERE IS ONE CONCLUSION I HAVE COME TO:

SKELETONS ARE THE HUNDREDS OF YEAR OLD DECOMPOSED HUMAN BODIES THAT WERE EITHER HAUNTED BY GHOSTS OR GAINED A MONSTER SOUL IN SOME WAY.

IT IS COMMON FACT THAT SKELETONS DON'T DECOMPOSE UNLESS IN WARM DAMP ENVIRONMENTS (AS FUNGI AND BACTERIA WILL BREAK THEM DOWN), HENSE WHY IT IS SO EASY TO FIND FOSSILS OR THE BONES OF DINOSAURS. SO SKELETONS CAN LAST FOR THOUSANDS OF YEARS. SO LET'S ALSO SAY, HYPOTHETICALLY, THAT SANS AND PAPYRUS WERE HUMANS AT ONE POINT AND DIED. AND THEIR TWO SOULS WOULD STILL BE STRONG ENOUGH TO GO BACK INTO THE BODY. (OR, BECAUSE THEY WERE DEAD, "SPIRITS" SAW THEIR BODIES STILL INTACT AND DECIDED IT CAN BE USED AS A VESSEL. OR IT COULD BE TWO RANDOM SPIRITS THAT JUST SO HAPPENED TO SEE THEM.) BUT IF THAT WERE THE CASE, HOW WOULD THEY HAVE DIED TO BE ONLY SKELETONS? WELL, CONSIDERING THEY'D BE HAUNTED, THEIR NORMAL BODILY FUNCTIONS WOULD EVENTUALLY START TO DECOMPOSE, SO FLESH AND MUSCLE WOULD START TO PEEL OFF THEIR BONES AND BASICALLY OOZE OFF. 

THIS COULD ALSO EXPLAIN WHY PAPYRUS AND SANS LIVE IN A COLD AREA, AS WARMER AREAS CAN CAUSE THEM TO START DECOMPOSING.

NOW ABOUT PAPYRUS AND HIS STATEMENT OF WHERE HE CAME FROM VIA THE INTERVIEW WITH PAPYRUS RELEASED BACK IN SUMMER OF THIS YEAR. HE STATED THERE WAS GRASS BEFORE BEING INTERRUPTED BY SANS STATING HE'S FREE TO TAKE A SHOWER. THIS MAY MEAN HE REMEMBERS THE SURFACE, BECAUSE THERE ARE NOT MANY PLACES IN THE UNDERGROUND THAT HAS GRASS. AND IF IT *IS* THE SURFACE THEN THAT MUST MEAN HE AND SANS ARE EXTREMELY OLD, CONSIDERING THE WAR AGAINST HUMANS AND MONSTERS TOOK PLACE HUNDREDS OF YEARS AGO. WHICH WOULD MEAN THAT IF THEY DID DIE LIKE I AM THINKING, THEY WOULD HAVE DIED BEFORE THE MASSIVE WAR AGAINST HUMANITY AND MONSTERS, OR DIED SOMETIME DURING IT. BUT THE ONLY THING STOPPING THIS THEORY IS THAT MONSTERS CAN NATURALLY DIE, SO I'M NOT SURE HOW BEING A SKELETON COULD AFFECT IT. AS WELL AS THE FACT THAT THERE COULD BE OTHER SKELETON MONSTERS SIMPLY NOT SHOWN ON SCREEN.

KEEP IN MIND THESE ARE MY PERSONAL ENTERPRETATIONS AND VIEWPOINTS, THIS DOESN'T MEAN I AM A RELIABLE SOURCE AND/OR THAT I AM RIGHT.