Why Do IQ Scores Vary by Nation?
Baker, Katie, Newsweek
Byline: Katie Baker
global differences in intelligence is a sensitive topic, long fraught with controversy and still tinged by the disgraceful taint of pseudosciences such as craniometry that strove to prove the white "race" as the most clever of them all. But recent data, perplexingly, has indeed shown cognitive ability to be higher in some countries than in others. What's more, IQ scores have risen as nations develop--a phenomenon known as the "Flynn effect." Many causes have been proposed for both the intelligence gap and the Flynn effect, including education, income, and even nonagricultural labor. Now, a new study from researchers at the University of New Mexico offers another intriguing theory: intelligence may be linked to infectious-disease rates.
The brain, say author Christopher Eppig and his colleagues, is the "most costly organ in the human body." Brainpower gobbles up close to 90 percent of a newborn's energy. It stands to reason, then, that if something interferes with energy intake while the brain is growing, the impact could be serious and longlasting. And for vast swaths of the globe, the biggest threat to a child's body--and hence brain--is parasitic infection. These illnesses threaten brain development in several ways. They can directly attack live tissue, which the body must then strain to replace. They can invade the digestive tract and block nutritional uptake. They can hijack the body's cells for their own reproduction. And then there's the energy diverted to the immune system to fight the infection. Out of all the parasites, the diarrheal ones may be the gravest threat--they can prevent the body from getting any nutrients at all.
Using data on national "disease burdens" (life years lost due to infectious diseases) and average intelligence scores, the authors found a striking inverse correlation--around 67 percent. …