Last night the movie Idiocracy premiered on Comedy Central. In it the Army's most average man is cryogenically frozen in an experiment, and is thawed out 500 years later in a world where he is the smartest man on Earth. Due to natural selection favoring people who don't use birth control and rampant consumerism the average IQ has dropped immensely. Most people seem barely able to read, they water crops with Gatorade (in fact water is just used in toilets), the landscape is a giant dust bowl covered with mountains of trash, and they spend their days watching pornos and "Oh, My Balls!" (a show consisting solely of a guy suffering groin injuries). Also Joe was ridiculed for being reasonable and "talking like a girl", up until they realized he was right about water being needed for plants and elected him president.
The scary thing is that this could actually happen, I know this sounds classist but people who have higher IQs and are better off tend not to reproduce as much as people who have lower IQs and are worse off. I'm sure you've noticed that lower class people tend to have more kids than upper and middle class people, largely due to the use of birth control. And I know how offensive it sounds but higher class people tend to be smarter than lower class people, unless they just inherited their wealth of course. Unfortunately there is no politically correct solution to this problem, eugenics has been just out of the question since the Holocaust and encouraging people with higher than average IQs to have more kids won't be enough. We could require mandatory genetic manipulation of all human embryos but that isn't technologically feasible yet and some will inevitably slip through the cracks (plus fundamentalists are unlikely to let it happen). Frankly the best thing we can do is encourage people with high IQs to donate sperm or eggs and use them exclusively for fertility treatments. Oh, wait, it's mostly upper and middle class people who can afford fertility treatments, we're screwed.