Until now, it was always assumed that this means that intelligence diminishes with age. However, this observation can be explained as well by noting that older people were raised in a period when the general level of intelligence was lower. Flynn showed that if people's IQ is evaluated with tests calibrated for the period during which they grew up, an old person scores as well as a young one. The reason that older people do less well on IQ tests is not that they have become more stupid with age, but that the younger generation simply got a head start. One might expect that the Flynn effect would be more clear for tests that emphasize culture or education.
Tests emphasizing traditional school knowledge show much less progress.
This means that something more profound than mere accumulation of data is happening inside people's heads. None of the scientists who have studied the effect can offer a simple explanation. Flynn himself admits that he is baffled by the results, and that he finds it hard to believe that his generation is significantly more intelligent than the one of his parents. He proposes the following argument. To me, it seems likely that this intellectual progress is caused by a combination of factors, just like the general progress in quality of life .