Actual big ass Halo spoilers
@starseeker @typhlosion
The Forerunners, Humanity, and the San’shyum (Prohpets) all existed at the same point and evolved separately, more than likely due to gene seeding from the “Precursor” race that became the Flood due to fucking up their stasis tech.
Humanity was trying to stop the Flood from spreading across the entire galaxy and as a result glassed a Forerunner civilian planet.