Just look at the quality of presidential debates and political discourse we've been having for the past decade. Not just in the US, but all over the world. The situation is perilous.
As someone said, it's no wonder The Matrix chose the 90s as the peak of human civilization.
IQ, (from “intelligence quotient”), is a number used to express the relative intelligence of a person.
So for the whole population it is constant by definition :)
And heading in the direction of Dick and Jane doesn't mean that we ever reached it; according to https://community.jmp.com/t5/image/serverpage/image-id/8926i... recent SOTUs should be comprehensible to high school freshmen.
(full discussion at https://community.jmp.com/t5/JMPer-Cable/Regression-to-model... ; through 2018 — anyone have 2022?)
EDIT: keep in mind that the expected "general" audience for the SOTU has also expanded dramatically due to technological change in between 1790 and 2018...
What is the mechanism you propose, by which the birth of a child makes every person now living incrementally dumber?
(Kids, if you ever see this, I'm not saying it wasn't worth it. But seriously, 2AM every night for months?)
Lagniappe: https://www.youtube.com/watch?v=EwPnJXXX5Ic