Infectious disease burden may be a major factor in determining national IQ differences

July, 2010

Analysis of global data shows that differences in national IQs are most strongly predicted by the country's infectious disease burden.

A new analysis of data first published in 2002 in a controversial book called IQ and the Wealth of Nations and then expanded in 2006, argues that national differences in IQ are best explained not by differences in national wealth (the original researchers’ explanation), but by the toll of infectious diseases. The idea is that energy used to fight infection is energy taken from brain development in children. Using 2004 data on infectious disease burden from the World Health Organization, and factors that have been linked to national IQ, such as nutrition, literacy, education, gross domestic product, and temperature, the analysis revealed that infectious disease burden was more closely correlated to average IQ than the other variables, alone accounting for 67% of the worldwide variation in intelligence. The researchers also suggest that the Flynn effect (the rise in IQs seen in developed countries during the 20th century) may be caused in part by the decrease in the intensity of infectious diseases as nations develop.

Reference: 

[1619] Eppig, C., Fincher C. L., & Thornhill R.
(2010).  Parasite prevalence and the worldwide distribution of cognitive ability.
Proceedings of the Royal Society B: Biological Sciences.

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