We’re getting stupider – and our ageing population may be to blame. Since around 1975, average IQ scores seem to have been falling. Some have attributed this to the evolutionary effect of smarter women tending to have fewer children. But new evidence suggests population-wide intelligence could in fact be sinking because people now live longer, and certain types of intelligence falter with advanced age.
For about a century, average IQ scores in wealthy nations rose in a steady and predictable way – by about three points a decade. This is thought to be thanks to improvements in social conditions like public health, nutrition and education. Since this trend – called the Flynn effect – was first noticed in the 1940s, it has been seen in many countries, from the Netherlands to Japan.
But by 2004, researchers had begun to notice what appears to be a reversal in this trend, with average IQ scores going into decline. “The drop is around 7 to 10 IQ points per century,” says Michael Woodley of the Free University of Brussels in Belgium.