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Human IQ is directly related to infectious diseases
Last reviewed: 30.06.2025
The mind is the most expensive thing in the world. Not in money, but in the currency common to all biology: energy. As one study showed, newborns spend almost 90% of the calories they receive on building and operating the brain. (In adults, this takes about a quarter of the assimilated energy.) If unexpected expenses arise in childhood, the brain will suffer. One such factor is an infectious disease.
It is known that the average IQ performs geographical miracles, changing not only from country to country, but also within them. The reason remains debatable - either genetics, or living conditions, or both at once. Nigel Barber argues that differences in IQ are explained primarily by differences in education. Donald Templer and Hiroko Arikawa believe that it is more difficult to live in a colder climate, so the IQ is higher there. Satoshi Kanazawa suggests that the IQ is higher the further from the African ancestral home of humanity (they say that there we survived without thinking, and beyond its borders it became more and more difficult).
Christopher Eppig, Corey Fincher, and Randy Thornhill decided to test all the hypotheses at once. Of all the factors (education, national wealth, temperature, distance from sub-Saharan Africa), infectious diseases were the best predictor of IQ. Christopher Hassall and Thomas Sherratt recently repeated this analysis using more sophisticated statistical methods and concluded that infectious diseases were the single most important predictor of national average IQ.
It also turned out that the five American states with the lowest average IQ (California, Louisiana, Mississippi, etc.) also have a higher level of infectious diseases, and the five “smartest” states (Massachusetts, New Hampshire, Vermont, etc.) are also the healthiest.
The hypothesis is supported not only by cross-national studies, but also by studies of individuals. For example, children infected with worms have been shown to have lower IQs later in life. Atheendar Venkataramani found that Mexican regions covered by malaria eradication programs had higher average IQs than other areas.
In practical terms, this means that human intelligence is a variable, not a constant, meaning it's not just genetics. If we defeat the infection, the whole world will become smarter.
It remains to be seen which periods of development are most sensitive to infectious diseases and which diseases are particularly harmful to the brain.
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