The creation of the Humani was not an accident - see the Necromancer. They were created when Zephaniah and Prometheus went to the Nameless City and entered the library. The library had clay statues that were brought to life by the power of Prometheus's aura.
Anubis was a genetic scientist that experimented to create the anpu, a jackal-humani hybrid.
it is quite ironic that his change made him look like his creations, the anpu.