What can you do to make your children smarter? The maintenance of good health might help. A new study suggests that differences in the world of intelligence can be explained by disparities in infectious diseases. The researchers found that the most severely affected by infectious diseases countries generally had the lowest average IQ. They propose that these diseases hinder brain development of children, although their conclusion is gathering mixed reviews.
The new research is based on data first published in 02 in a controversial book called IQ and the Wealth of Nations . In the book, the psychologist Richard Lynn of the University of Ulster UK and Tatu Vanhanen political scientist at the University of Tampere in Finland searched the published literature to come up with average IQ measures for 81 countries. They also estimated IQ for another 104 countries by averaging the neighboring nations IQ. Hong Kong topped the list with an average IQ of 107. The authors argued that national differences in IQ at least partially explained the differences in national wealth. In 06, they expanded the data to include IQ measures 113 countries and new estimates for 79 others.
Several groups have attempted to explain the reason. In the new study, Christopher Eppig, a doctoral candidate in biology at the University of New Mexico, Albuquerque, and colleagues propose that low IQ is related to the number of infectious diseases. Their idea, the researchers call the "parasite-stress hypothesis" is that children who become "parasites", which they define to include everything from intestinal worms to bacteria and viruses, devote more energy the fight against infection. therefore, they have less energy available to brain development. the countries where infectious diseases are prevalent, Eppig and his colleagues say, have lower intelligence.
to test this idea, the researchers analyzed statistically the relationship between 06 Lynn and Vanhanen data and 04 data on the burden of infectious diseases to the World health Organization, which measures the potential years of healthy life lost to premature death and disease as a result of 28 infectious diseases, including malaria, hepatitis and tetanus. the researchers also reviewed factors that other research groups had related to IQ, such as nutrition, literacy, education, gross domestic product, and temperature.
The figures appear to confirm the hypothesis, the team will report online tomorrow in the Proceedings of the Royal Society B . When the researchers analyzed each factor separately, they found that the burden of infectious diseases was more closely correlated with IQ than other variables. "Parasites alone represent 67% of the variation around the world in the mind," says Eppig. To further evaluate the relationship, the researchers constructed a statistical model that allowed them to test the predictive power of the load infectious diseases against other variables previously associated with IQ, such as education, temperature, distance from sub-Saharan Africa, and wealth. burden of infectious disease again came out on top, though temperature and distance SSA explained some of the changes as well.
Eppig stresses that their study can not rule out any of the other factors. "I would never say that parasites are only thing that affects the global diversity of intelligence. "
Maureen Black, a pediatric psychologist at the University of Maryland School of Medicine in Baltimore, is skeptical. It argues that health itself is not enough for the full development of the brain. "For children to develop intellectual skills they need not only solid objects and the absence of infections, they also need opportunities to explore and enrichment opportunities." These opportunities could be lacking in countries with low average IQ.
But Richard Guerrant, MD, an infectious disease expert at the University of Virginia School of Medicine in Charlottesville, says researchers are on the right track. His work suggests a link between diarrheal diseases, malnutrition, stunted growth, and lower IQs. The next challenge, he says, will be to discover the exact mechanisms.
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