“How to Raise the World’s IQ” reads the promising cover of the July 13 issue of The Economist. Moms and babies need to eat more nutritious foods, which will help them resist contagious diseases. If they do, people will be taller and enjoy enhanced brain muscle.
Average intelligence levels of the world’s population have been climbing for a century or more. Scientists have known for decades that nutrition feeds the brain, just as it does the rest of the body, but only now has a major news outlet provided details about the connection between nutrition and IQ levels. The British magazine touches lightly on the progress that has been made, then concentrates on the distance yet to be traveled. It laments poverty, warfare, famine, corruption, government regulations, and misguided food choices that together expose millions of children to malnutrition.
By doing so, The Economist corrects the widespread, deeply engrained understanding of intelligence as a trait solely determined by our genetic endowment. Textbook theories of intelligence tell us the human brain has evolved slowly over thousands of millennia through processes of Darwinian natural selection. The intellectually “fit” have survived and procreated.
That view is not so much wrong as it is incomplete. During the 1980s, James Flynn, a New Zealand political theorist, reported that adults who were then taking an IQ test were scoring about 15 points higher than those who had taken a comparable test in the 1930s. Geneticists initially scoffed at this novel finding, but subsequent studies also recorded an average gain of approximately three points a decade in the kind of intelligence known as fluid reasoning, the strand used to solve abstract problems such as those encountered in mathematics.
Dany Shakeel of the University of Buckingham and I have tracked gains between 1970 and 2015 in U.S. math performance at age nine (see “A Half-Century of Student Progress,” research, Fall 2022). Scores improve by as much as the upward trend in fluid reasoning over the same period, suggesting that young children in the United States have been getting smarter by the decade. However, gains in reading are less than a fourth the size as those in math. In addition, we find math growth to be greater for Black and Hispanic students than for white ones. Gains are especially large for Asian students. We also find improvement larger among those in the lowest quartile of the socio-economic distribution than among those in the highest quartile.
Three explanations may account for the improved test performance of students in the United States. First, families in the United States have become steadily smaller and more prosperous, better educated, and informationally rich, creating a better home environment for children. Second, schools may be more effective than ever before. More money is spent on education than 50 years ago, class sizes are smaller, schools are less segregated, resources are allocated more equitably, and school children now receive a wide variety of ancillary services.
Third, improved nutrition and health care has enhanced brain development during what is known as the golden period, the approximately 1,000 days between conception and the age of two, a time when brains are rapidly developing. If babies receive needed nutrients, both before and after they exit the womb, and if nutrients do not need to be used to counter contagious diseases or environmental insults, they will later enjoy greater capacity to reason with fluidity.
The three explanations are complements, not rivals, but the editors of The Economist make a strong case for the importance of the third one by highlighting the prevalence of stunting in many poor countries, a physical impairment researchers attribute in part to serious malnutrition. Relying on data from the World Health Organization, they claim that in the United States the percentage of children far too short for their age has hovered around 2 percent between 2000 and 2022. Over the same period in China, the stunting rate has dropped from 20 percent to the same level as in the United States. In Bangladesh, where public policy has focused on enhancing early childhood nutrition, the percentage stunted fell from about 50 percent to 20 percent, a sharp contrast with the Philippines, which shows only about a 5 percentage-point decline from its 30 percent stunting rate at the turn of the century.
Worldwide, the average height of the world’s population has shifted upward by 4 inches over the past century. Although The Economist focuses on extreme cases like stunting, the connection between nutrition and IQ is much broader. Steady nutritional advances over the course of the last 100 years have yielded continuous gains in aptitude and ability, just as in height.
Growth in stature and intelligence will not continue forever. We should not envision Gulliver’s world of 12-foot giants or a land inhabited by Einsteins any time soon. As economists like to say, the returns to investment diminish at the margin. IQ returns to improved nutrition, disease reduction, and environmental risk may have already begun to reach the vanishing point in the most advanced industrialized societies. If the recent declines on the National Assessment of Educational Progress are any sign, this could be true for the United States.
Still, better care of the youngest, most fragile members of society across the globe could yield substantial gains in world intelligence. The Four Horsemen of the Apocalypse—death, war, pestilence, and famine—still ride. We have yet to eradicate unhealthy diets, wrong-headed regulations, and corrupt systems of food distribution, to say nothing of armed conflict, starvation, and contagious diseases. Hopefully, someday we will be intelligent enough to do so.
