Rising Scores on Intelligence Tests
Test scores are certainly going up all over the world, but whether intelligence itself has risen remains controversial
Today's average adult from an industrialized nation stands much taller than the comparable adult of a century ago. That increase in stature—almost certainly the result of general improvements in nutrition and health—has come at a rate of more than a centimeter per decade. Available data suggest that these gains have been accompanied by analogous increases in head size, and presumably by an increase in the average size of the brain. Richard Lynn of the University of Northern Ireland argues that this is the only significant cause of the Flynn effect: Larger brains produce higher levels of intelligence. According to his interpretation, the rise in test scores is no artifact; it indexes genuine gains in cognitive ability.
The most obvious objection to Lynn's proposal is that it explains too much. To treat the gains as genuine and essentially biological is to concede that we are indeed vastly more intelligent than our grandparents—a conclusion that seems intuitively unpalatable. There is also an empirical problem: It is difficult to demonstrate the direct connection between diet and intelligence that the hypothesis requires. Severe malnutrition in childhood almost certainly produces negative cognitive effects, but the fact that it usually occurs together with other forms of deprivation makes those effects difficult to analyze. Experimental studies involving dietary supplements have rarely included adequate control groups, and the few studies with what seem to be positive results have proved difficult to replicate. Although it is sometimes suggested that malnutrition produces a greater effect on visual-spatial than on verbal skills—which would be compatible with the pattern of observed long-term gains in test scores--this too has not been firmly established. Taken together, the evidence linking nutritional levels to intelligence is shaky at this point.