Soil fertility alone explains 34% of the differences in national IQ. Countries on the best soils (Mollisols, Andisols) average 10–15 IQ points higher than those on the wort soils (Oxisols, Ultisols), even before accounting for education or income.
This geographic pattern is visible in real populations. Japan and Taiwan sit on volcanic Andisols and consistently rank among the highest in global intelligence metrics due to their nutrient‑rich, high‑CEC soils. Meanwhile, much of equatorial Africa rests on Oxisols, soils so weathered and nutrient‑stripped that they produce chronically low micronutrient availability.
The further a soil’s pH drifts from 6.5, the more national IQ (MNIQ) declines. If your soil is too acidic (like much of the tropics), zinc and iron become unavailable. If your soil is too alkaline (like the Middle East), micronutrients get locked up too. The correlation between soil fertility and national IQ is r = 0.58, meaning soil alone accounts for 34% of the variation. Explaining 34% of a complex human trait is extremely high.