[ quick and brief ] recalling an explanation of why something changed in people suddenly - one day - in 1800’s - THE day ELECTRICITY GENERATORS were turned ON in NewYorkCity.
Same thing gradually worked its way as ELECTRICITY was added to more and more areas.
Reason: Prior to electricity, people heated with wood, wood ashes FERTILIZED their food/gardens. ERGO all the GOOD NUTRIENTS they got that way - had stopped when that stopped with the using of electricity.
(This may take exception to immigrants having poorer nutrition.)
This would indicate that Africans who burn wood should have higher IQ than city-bred Europeans. Doesn't seem to be the case.