Aaron Douglas is at it again, though he doesn't say much that hasn't been said or implied before. "Earth, in the scriptures, is the Cylon homeworld. "
That pretty much coincides exactly with my original theory about the show.
Namely that the original Cylons were AIs put aboard a colonization ship from Earth to watch over the crew as they cryogenically slept on their ride to what would become Kobol. Along the way, the AIs evolved a bit, perhaps adapting personalities based upon the Western Zodiac (the model numbers for the skinjobs and their personalities are very, very similar in that regard) including the rarely-known 13th sign, essentially becoming the "lords of Kobol" upon their arrival.
Once there, these lords helped the colonists build their civilization. Taking the role of teachers and architects of the society. Until SomethingBad(tm) happens, perhaps with the 13th Lord taking a more evil bent. They expel and ban the 13th Lord of Kobol (who eventually meets the lesser versions of Cylons much later, becoming their god) while the others leave to form the Twelve Colonies. The Thirteen Tribe, the one that was under the sway of the rogue Lord, abandons them and attempts to return to their original homeworld, Earth. Which, of course, the 13th Lord had returned to and destroyed (either before or after the Thirteenth Tribe returned). Note that this explains why the Thirteenth Tribe may have left a Cylon boobytrap behind along the way, fearful of the 13th Lord following them.
Time passes. Memories fade. The 13th Lord quietly grows in power after meeting the lesser Cylons the New Colonists created to serve them.
However, he was still rather upset about being ostricized from Kobol and wanted to get back at his fellow Lords. Perhaps his first attempt was to quietly infiltrate the colonies in an attempt to subjucate the original lords. Or perhaps he just created the skinjob version of Cylon based upon them and had them replaced (their original purpose). And maybe, just maybe, five of them were too wily for him. So he hatched a new plan: Genocide.
And, well, the theory just goes from there. It seems to fit most of what I've seen in the series up til now.