THE FLYNN EFFECT is the huge increase in average performance on intelligence tests from 1920 to 1995. A score of 100 is by definition average, but only at a point in time. Scoring 100 in 1995 meant that someone did much much better on the test than someone in 1920.

A good reference on this is The Rising Curve , edited by Ulric Neisser (1998). The cause does not seem to be better nutrition; score variance is unchanged, or diminishes only because of ceiling effects (p. 44), so it is not that severely malnourished children are diminishing in number, and there is no reduction in the Netherlands after the deprivation of World War II. TV is not the cause; the increase was at the same rate before and after TV was introduced (p. 47). I feel dissatisfied with the book, though. I'd like to see IQ gains compared with height gains, and I'd like some quantitative estimates of how big selection effects would have to be (high-IQ people being more fertile) and of the effect of smaller family sizes generally, which means more children are high-IQ first-borns.