I've always kinda wondered about this. Even the humans on Marvel's earth didn't evolve naturally...the Celestials mutated primates to create them, the Deviants and the Eternals. We know the Inhumans were the Kree's experiments on Earth's primates using what they learned from the dissection of an Eternal. We know the Lemurians are an offshot of the Atlanteans that left the Atlantic Ocean for the Pacific Ocean, found the serpent crown and turned green and scaly. But where do the Atlanteans actually come from?
We know that before the great cataclysm there were human cities called Atlantis and Lemuria but they sank into the sea. The human Atlantis (presumably the same general area as the Atlantis related in Kull's earlier time period) was like the last city not controlled by the Deviants while the Lemuria above the seas was the capital of Deviant empire. Thousands of years after Atlantis sank into the ocean the Homo Mermanus found the city and built their own Atlantis on top of it (and presumably the ones who later left this Atlantis for the Pacific found the Lemuria that fell into that ocean even though I think there is still a Deviant City called Lemuria that is underground and not in an ocean).
Ok so thousands of years after human Atlantis sank the Homo Mermanus squatted there and built their own city. What do we know about them prior to that?
Almost every other major faction on earth has had some genetic modification made. Were the Atlanteans created by an alien power? Or are the Atlanteans what happens to the primates whose genetics were not tampered with by the Kree and the Celestials?
We have three theories:
2. Gods (Greek?).
And then Hickman gave us those Old fishy Atlanteans.
My interpretation of the original Celestials story is that 100% of the human race was tampered with, and that explains ALL superpowers and lays the groundwork for all of the racial offshoots. Humans were divided into three groups: Eternals, Deviants, and the Rest (the latter of which were given the propensity to mutate, be it X-Genes, other superhuman mutations, or other subraces).
I also don't like any of the pantheons being older than mankind. But that's just me.