Scientists found a link between soil fertility and national IQ levels

A peer-reviewed study published in Scientific Reports has identified a geographic correlation between soil fertility and estimated national IQ scores across 126 countries. The authors report that regions with more agriculturally productive soils tend, on average, to coincide with higher measured cognitive test scores at the country level, based on aggregated datasets compiled from public sources.

The research, led by soil scientist Sabit Erşahin, has been framed as an exploratory attempt to examine whether long-term environmental factors linked to agriculture and nutrition may be statistically associated with population-level cognitive outcomes.

Data and methodology

The analysis constructed a “Soil Fertility Index” combining global soil classification data with deviations in soil pH from an assumed optimal level for agriculture. Soils such as Mollisols, typically associated with high organic content and agricultural productivity, were assigned higher fertility scores, while highly weathered tropical soils such as Oxisols received lower scores due to reduced nutrient retention capacity.

These environmental indicators were then compared with country-level IQ estimates sourced from aggregated international datasets. The authors applied geostatistical techniques, including spatial correlation analysis, to assess whether patterns in soil fertility and cognitive score distributions exhibited similar geographic clustering across continents.

Key findings

The study reports a moderate positive correlation between soil fertility and national IQ estimates (r = 0.58), suggesting that countries with higher soil fertility indices also tend to show higher average cognitive scores in the dataset. According to the authors, soil fertility accounted for approximately 34% of the observed variation across countries, though the majority of variation remained unexplained.

The analysis also found that lower fertility regions—particularly in parts of the tropics and certain arid zones—tended to cluster with lower average scores in the dataset, while higher fertility zones in temperate regions showed the opposite pattern. However, the authors emphasize that these results reflect statistical association at the country level rather than individual outcomes.

Interpretation and limitations

Researchers involved in the study caution against interpreting the results as evidence of causation. The authors highlight that numerous confounding variables—including education systems, income levels, healthcare access, governance, food imports, and cultural factors—are not fully captured by the soil-based model.

They also note the risk of ecological fallacy, where correlations observed at the national level may not apply to individuals. “Correlation is not causation,” the study’s lead author stressed, adding that soil fertility should be considered only one of many potential environmental correlates rather than a determining factor in cognitive development.

Broader implications

The authors suggest that soil fertility may indirectly influence human development through its role in shaping agricultural productivity and dietary micronutrient availability, particularly elements such as iron, zinc, and iodine that are essential for brain development. However, they stress that these pathways remain hypothetical and require further multidisciplinary validation.

The study positions itself as an early-stage exploratory analysis rather than a definitive explanation of cross-country differences in cognitive outcomes. The researchers call for more detailed datasets incorporating soil chemistry, crop nutrition, public health, and socioeconomic variables to better understand complex developmental outcomes over time.

Source: PsyPost