There appears to be a number of studies showing that mankind seems to be experiencing a reversal of its IQ growth. There is a phenomenon called Flynn effect that means that mankind's average IQ grew steadily 3 points per decade until 1970s, but that process seems to have stopped now and even reversed, in other words, humanity's average IQ is falling.
Norwegians published a study that shows an average IQ fall of up to 7 points with each successive generation up to 1991. As to the causes of this trend, Norwegians established that genes/family ties have little to do with it and the root cause of the IQ fall seems to be cultural.
The IQ drop has been observed also elsewhere:
France
https://notpoliticallycorrect.me/2016/09/29/are-flynn-losses-in-france-due-to-immigration/Germany
https://www.sciencedirect.com/science/article/pii/S0160289615001336
