The Flynn effect is misunderstood to be some sort of general humanist truth (because psychology classes generally present it as such), but the existence of a reversal in the Flynn effect in recent years may indicate that it was just a circumstance of the 20th century and not something that we can assume will continue forever.

Flynn effect and its reversal are both environmentally caused (2018)

https://sci-hub.tw/https://www.pnas.org/content/early/2018/0...