: It's much more believable and richer than humanity simply being the
: Forerunners who personally regressed themselves when they needed their
: ingenuity the most. Such a grand species going from a Halo to a cave of
: their own accord is something I really doubt would ever happen. Even then,
: Bungie's intentions with the Human-Forerunner connection seems vague. 343
: Guilty Spark speaks very strangely. He refers to John like they've met
: ions ago, and despite being almost entirely human, is referred to as a
: Forerunner. It honestly seems like 343i's geas and related structures are
: rooted well in Bungie's mythos for Halo.

My take on the intent of the Halo 3 Terminals was that the Precursors took primitive human stock from Earth in the distant past and genetically modified them to become the Forerunners. (This matches with Precursor info in the Bestiarum). Then the Forerunners do their thing while humanity evolves on Earth.

Around the time just before the firing of the Halo Array, the Librarian is cataloging/indexing sapient species and discovers Earth. She notes that humans are special and may provide a link to the Forerunners' past. (H3 Terminals)

This matches up with Guilty Spark's reference to the Master Chief that he "is Forerunner", as Guilty Spark either detects or is fully aware of the events of the past.

There was no need of technologically advanced humans in the distant past or a devolved legacy from which humanity had to re-ascend. Plus the idea of directed evolution and "end result" more than suggests the writers don't actually understand how evolution really works.