Flynn effect is fascinating me - if it holds in the future we'll have, in developed nations, an average IQ of 130 (by today's standards) in 100 years. That's a LOT. It'd, roughly, mean that ~17% of people would be capable of graduating from today's Ivy League schools without problems (145 IQ or more). And there would still be the (new) top 0.5%. But whether it will hold is anyone's guess.
Black IQ Gains in Britain, Kenya and Dominica
https://robertlindsay.wordpress.com/2011/01/19/black-iq-gain...
Eyeferth Study -- Children of Black American servicemen in Germany had the same average IQ as German children:
https://en.wikipedia.org/wiki/Eyferth_study
Thomas Sowell's survey of the work of Arthur Jensen and others. Basically, the patterns around the Flynn Effect are everywhere, and it shows up in Black populations as well. There is also a mention of a study of Black children raised by white families, which found the average IQ of that population to be 106.
https://www.nytimes.com/1977/03/27/archives/new-light-on-bla...
It isn't holding, especially in isolated populations that are easy to measure like Iceland.
Most probably it was due to the increasing ubiquity of K-12 education and fewer bad childrearing habits (smoking/drinking while pregnant, lead exposure, no vitamins).