AKQA, the company responsible for last year's award-winning IRIS ARG promoting Halo 3, has put up an extensive presentation that summarizes and details each step of the game.

In episode 4, the summary reads in part:

The fourth episode continued to provide hints at the previously unknown Halo backstory, including the shocking reveal that Humans and Forerunners share an ancient biological connection.

So, is that it? Are humans and forerunners somehow related? Are Humans surviving Forerunner, left behind somehow when the latter moved out into space? Is Earth a lost Forerunner homeworld? Do they merely share a common lost ancestor-- the Precursors, perhaps? Were both species, Human and Forerunner, seeded by some other, unknown source? Is this official backstory given to AKQA by Bungie, or something they came up with themselves?