I watched the movie Idiocracy the other day, and it got me thinking. Everywhere you look, it seems like stupid people are breeding like rabbits, while more intelligent people have few or no children.
Even though it's a comedy, I think the first 10 minutes of Idiocracy illustrates this concept well.
A certain amount of intelligence is genetic (genotypic IQ). Some scientists estimate that to be as much as 70%. And more intelligent people have fewer children than less intelligent people. In the US, average SAT scores by state were compared with fertility rates (number of children a person has) by state, and found that the more intelligent a person is, the fewer children they have. (Another study showing the correlation between education and fertility can be found here).
Additionally, a study conducted at the University of Ulster found that the world's IQ is declining. They found that from 1950 - 2000, the world's IQ declined by 0.86 IQ points. They project that between 2000 and 2050, the world's IQ will further decline by 1.28 IQ points.
So it seems that society really is getting dumber.