The research suggests that genes aren't what's driving the decline in IQ scores
"It's not that dumb people are having more kids than smart people," researcher says
IQ scores have been steadily falling for the past few decades, and environmental factors are to blame, a new study says.
The research suggests that genes aren’t what’s driving the decline in IQ scores, according to the study, published Monday.
Norwegian researchers analyzed the IQ scores of Norwegian men born between 1962 and 1991 and found that scores increased by almost 3 percentage points each decade for those born between 1962 to 1975 – but then saw a steady decline among those born after 1975.
Similar studies in Denmark, Britain, France, the Netherlands, Finland and Estonia have demonstrated a similar downward trend in IQ scores, said Ole Rogeberg, a senior research fellow at the Ragnar Frisch Center for Economic Research in Norway and co-author of the new study.
“The causes in IQ increases over time and now the decline is due to environmental factors,” said Rogeburg, who believes the change is not due to genetics.
“It’s not that dumb people are having more kids than smart people, to put it crudely. It’s something to do with the environment, because we’re seeing the same differences within families,” he said.
These environmental factors could include changes in the education system and media environment, nutrition, reading less and being online more, Rogeberg said.
The earlier rise in IQ scores follows the “Flynn effect,” a term for the long-term increase in intelligence levels that occurred during the 20th century, arguably the result of better access to education, according to Stuart Ritchie, a postdoctoral fellow in cognitive ageing at the University of Edinburgh whose research explores IQ scores and intelligence and who was not involved in the new study.
Researchers have long preferred to use genes to explain variations in intelligence over environmental factors. However, the new study turns this thinking on its head.
Intelligence is heritable, and for a long time, researchers assumed that people with high IQ scores would have kids who also scored above average. Moreover, it was thought that people with lower scores would have more kids than people with high IQ scores, which would contribute to a decline in IQ scores over time and a “dumbing down” of the general population, according to Rogeberg.
Anyone who has seen the film “Idiocracy” might already be familiar with these ideas. In the scientific community, the idea of unintelligent parents having more kids and dumbing-down the population is known as the dysgenic fertility theory, according to Ritchie.