After 2 weeks of Halo I've finally discoverd they're origin:THE FLOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOD!
Ok so Morgan freeman ()Was inter-bred with the one and onlyZOIDBERG!
Then Chuck Norris thought they were Mexicans so he tried to beat them to death with round-house kicks and paralyzing punches so then he got tired of it and shot them into space and the flood conveint-ly landed on gods missing marrage ring and so in fear of being killed they hid in a structure for ever feeding off of tacos.