LogFAQs > #902061225

Bungie also intended ancient humans themselves to be the Forerunners (which makes so much sense considering all the hints they gave in the original trilogy*; more on that below), but 343 decided to change that up in order for the Didact/Prometheans as antagonists thing to make sense. I kinda like it 343's way better. I always wanted to know "what the hell did the Forerunners look like?!" and it scratched that itch, and Bungie's way would have contradicted scientific knowledge about human origins and instead co-opted the crypto-conspiracy that humans are aliens from another planet.

*Guilty Spark's lines throughout Halo 1 where he treats Master Chief like he should know what the halo is and what's going on, and where he accesses the PoA's databanks as says something like "[I finally have] a record of all our lost time! 'Human history', is it? Fascinating..." And also the line at the end of Halo 3 where he straight up tells Chief "you ARE Forerunner".

*The portal to the Ark being built on Earth and humans being the only ones capable of operating the most important Forerunner tech (admittedly not strong evidence considering it fits just as nicely into 343's take of humanity simply being the Forerunners' chosen successor race).

*The much more extreme poetic irony of the Prophets declaring a genocide upon their own gods themselves instead of just their gods' chosen ones.