Reducing and preventing infectious disease leads not only to healthier populations, but also to smarter ones, says a paper recently published in Proceedings of the Royal Society. It’s been previously shown that there is a global variation in intelligence, and that richer, more developed countries have higher average IQs. The paper analyzes several possible factors in this variation, and comes to the conclusion that prevalence of infectious disease is the best predictor of average national IQ.
Their theory, which the authors call the parasite-stress hypothesis, states that infectious disease adversely affects the developing brain because it diverts energy from the brain’s growth to dealing with the parasites. If the growing brain doesn’t get the nutrients and energy it needs, then it will not develop as well as a sufficiently nourished brain, which therefore leads to lower intelligence. The authors do note that parasite stress is likely not the only cause of the global variation in intelligence, but is most probably one of a number of contributing elements.
Interestingly, previous studies have shown that the frequency of asthma and allergies correlates with both higher intelligence and reduced exposure to pathogens. This leads the paper’s authors to hypothesize that the relationship between intelligence and autoimmune diseases might be dependent on exposure to infectious diseases. If a developing child is exposed to fewer infectious diseases, the brain can develop better; however, the body then doesn’t have as many infections to fight, and perhaps it turns on itself as a result.
The study certainly raises a number of issues, including the validity of IQ tests as a measure of intelligence, and issues about how to combat vicious circles (countries are poor because they are sick, and are sick because they are poor). However, setting those aside, the findings seem to underscore the importance of preventing infection to keep us both healthy and smart.
The link to the full text of the paper is here: http://rspb.royalsocietypublishing.org/content/early/2010/06/29/rspb.2010.0973.full