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An analysis of some 730,000 IQ test results by researchers from the Ragnar Frisch Centre for Economic Research in Norway reveals the Flynn effect hit its peak for people born during the mid-1970s, and has significantly declined ever since.

https://www.sciencealert.com/iq-scores-falling-in-worrying-reversal-20th-century-intelligence-boom-flynn-effect-intelligence

Peak and fall. More likely a population crash due to mute load.