Yeah, fair point. I was pointing to the fact that intelligence differences (though as you say, not described as IQ differences at that time) were used as justification for those things. Black people were described as "incorrigibly stupid" denied the right to education, etc, etc so their mistreatment could be more easily justified.

And yes, I thought about mentioning the Flynn effect. It ended up feeling a bit shoehorned in as it doesn't relate directly to race, so it didn't make the final draft.😄