People Everywhere Are Getting Smarter
About half of Americans two generations ago would have been diagnosed as mentally retarded based on today’s IQ tests.
In 1980, the New Zealand political scientist James Flynn discovered that average IQs in many countries have been drifting upward at about 3 points per decade over the past couple of generations. In fact, the average has risen by an astonishing 15 points in the last 50 years in the United States. In other words, a person with an average IQ of 100 today would score 115 on a 1950s IQ test, and a person of average IQ today would have been in approximately the top 15 percent of same-age scorers 50 years ago. If the average American kid were to take the first Stanford-Binet IQ test from 1932, she would score about 124 points today.
“This means that on an IQ test made in 1930 the average score of the entire population would give an IQ between 120 and 130 according to the original standardization,” the Hungarian technologist Kristóf Kovács explains. So “instead of 2 percent, 35–50 percent of the population would have an IQ above 130. And vice versa; if the current standard was applied to people living in 1930, average IQ would be between 70 and 80, and instead of 2 percent, 35–50 percent would be diagnosed with mental retardation.”
What accounts for this massive increase in IQ scores? Researchers have suggested a panoply of causes, including better nutrition, exposure to more mentally challenging media, and more formal schooling, but my favorite is the reduced load of infectious childhood diseases.
A fascinating study published in the June 2010 Proceedings of the Royal Society by the University of New Mexico biologist Christopher Eppig and his colleagues finds an intriguing correlation between the average IQ of a country’s citizens and the intensity with which they suffer from parasites and infectious diseases. The authors note that the brains of newborns burn up 87 percent of infants’ metabolic energy; 5-year-old brains use 44 percent; and adult brains consume 25 percent of the body’s energy. Mobilizing the immune system to fight off diseases and parasites is very metabolically expensive, diverting nutrients and energy that would otherwise be used to fuel the building and maintenance of the human brain. If this analysis is substantially correct, then promoting public health also promotes higher IQs.
The new study reports, “Infectious disease remains the most powerful predictor of average national IQ when temperature, distance from Africa, gross domestic product per capita and several measures of education are controlled for. These findings suggest that the Flynn effect may be caused in part by the decrease in the intensity of infectious diseases as nations develop.”
The converse of this research should find a correlation between higher average IQs and increasing allergy and asthma rates. Allergy and asthma rates are hypothesized to be on the rise because children’s immune systems, no longer challenged by infections, have become oversensitive, attacking the bodies they are supposed to protect. Myopia also correlates with higher IQ scores; U.S. myopia rates in people ages 12 to 54 increased from 25 percent in 1971–72 to 41.6 percent in 1999–2004. But higher IQ correlates with better health and longer lives, less propensity to commit crimes, and higher income (although not greater than average personal wealth).