Allyson in Bureaucracy:
But you know how it is, the tribe wants to beat the stupid person to death lest it procreate and make dozens of stupid people and then the tribe is inundated with the stupid, and so people have to leave the tribe in the middle of the night while the stupid people get all the really cool huts to themselves. But then the stupid people can't keep the fire going, because they're so fucking stupid, and eventually they freeze to death, and the camp becomes a wasteland.
Then the archaeologists come and see the broken clay pots of the once mighty civilization and theorize that an outbreak of measels killed everyone off, but really, it's just that the stupid people took over, and the smart people left to go invent the wheel, someplace else.