By the way, here's the (really cool) paper showing an IQ rise followed by an IQ decline in Norway. It argues both are almost completely caused by (as-yet-unknown) changes in the environment:
IQ increased throughout the 20th century, but this trend has recently slowed down or even reversed in a number of countries. The causes of the rise and fall of IQ appear to be largely environmental, but we have little idea what those causes might be.
The Flynn effect, a rise in intelligence over the 20th century, and its recent reversal, are based on environmental causes, but their nature remains a puzzle.
Really cool study (though that it's environmental was already so well accepted, given speed it happened, that it underlies a lot of arguments about whether various gaps are): "Flynn effect and its reversal are both environmentally caused"
Another intriguing fact is that some countries are seeing a negative Flynn effect in cohorts exposed to more education: It appears that not all education is the same.
Flynn effect and its reversal are both environmentally caused
Flynn effect reversal environmental says
IQ is apparently declining steadily in a very broad-based way. In PNAS "Flynn effect and its reversal are both environmentally caused"