...or read.

At least in the USA: 21% of adults in the US are illiterate in 2024. 54% of adults have a literacy below a 6th-grade level [1].

1: https://www.thenationalliteracyinstitute.com/2024-2025-liter...

Hasn't this always been an intelligence thing? I think across all societies and eras we find that generally a a rather alarmingly large section of population is unable to grasp basic written instructions - and that section usually increases to the majority of people, when we start getting into things like an employment contract, or mortgage document.