In a nutshell, humans are a science experiment that was thrown out and forgotten. Lo and behold, we grew into the "dominant" species on the planet Earth.


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I say forgotten because in At the Mountains of Madness, the revived Elder Things dissect a human to see how he works. If they created him, they wouldn't have needed to do so. Thus, I have concluded that when they made humans, they weren't as advanced or developed as what the awoke to find aeons later... So in essence, we were forgotten, perhaps in exchange for more... useful... experiments. IE: Shoggoths.