[mapt]

It's because there are multiple levels of misconceptions as well as "violent agreements".

retsibsi is correct. You can't draw (meaningful) conclusions about IQ before 1950, because extrapolating from the data after 1950 is dumber the farther back you reach, just for reasons related to the concept of extrapolation.

This has nothing to do with the fact that IQ is a statistical distribution that we keep re-norming, which "should always average 100"; The Flynn Effect is not in serious dispute, it's just an effect that pertains to nonstandardized results.