Idiocracy wasn't a movie, but a documentary. Gerald Crabtree, the leader of a genetics laboratory at Stanford University, argues that humans evolved to be hunter/gatherers--a high risk occupation that tended to keep the gene pool tidy. We have departed from that self-correcting lifestyle:
Life as a hunter-gatherer was probably more intellectually demanding than widely supposed, he says. “A hunter-gatherer who did not correctly conceive a solution to providing food or shelter probably died, along with his or her progeny, whereas a modern Wall Street executive that made a similar conceptual mistake would receive a substantial bonus and be a more attractive mate,” Professor Crabtree says.
But are there any data to back this up?
A comparison of the genomes of parents and children has revealed that on average there are between 25 and 65 new mutations occurring in the DNA of each generation. Professor Crabtree says that this analysis predicts about 5,000 new mutations in the past 120 generations, which covers a span of about 3,000 years.
Other scholars are skeptical of Crabtree's hypothesis. Steve Jones of University College London thinks that trying to tie intelligence to mutation count is a stretch:
“I could just as well argue that mutations have reduced our aggression, our depression and our penis length but no journal would publish that. Why do they publish this?” Professor Jones said.