A pair of researchers with the Ragnar Frisch Centre for Economic Research in Norway has found that IQ test scores have been slowly dropping over the past several decades. In their paper published in Proceedings of the National Academy of Sciences, Bernt Bratsberg and Ole Rogeberg describe their study and the results they found. They also offer some possible explanations for their findings.

Prior studies have shown that people grew smarter over the first part of last century, as measured by the intelligence quotient—a trend that was dubbed the Flynn effect. Various theories have been proposed to explain this apparent brightening of the human mind, such as better nutrition, health care, education, etc, all factors that might help people grow into smarter adults than they would have otherwise. But, now, according to the researchers in Norway, that trend has ended. Instead of getting smarter, humans have started getting dumber.

The study by the team consisted of analyzing IQ test results from young men entering Norway’s national service (compulsory military duty) during the years 1970 to 2009. In all, 730,000 test results were accounted for. In studying the data, the researchers found that scores declined by an average of seven points per generation, a clear reversal of test results going back approximately 70 years.

But it was not all bad news. The researchers also found some differences between family groups, suggesting that some of the decline might be due to environmental factors. But they also suggest that lifestyle changes could account for some of the decline, as well, such as changes in the education system and children reading less and playing video games more. Sadly, other researchers have found similar results. A British team recently found IQ score results falling by 2.5 to 4.3 points every decade since approximately the end of the second world war. And this past December, another group from the U.S. found that children who grew up eating a lot of fish tended to have higher IQs—and they slept better, too, which is another factor involved in adult intelligence levels. Notably, children in many countries in the modern era eat very little fish.

More information: Bernt Bratsberg et al. Flynn effect and its reversal are both environmentally caused, Proceedings of the National Academy of Sciences (2018). DOI: 10.1073/pnas.1718793115

Abstract
Population intelligence quotients increased throughout the 20th century—a phenomenon known as the Flynn effect—although recent years have seen a slowdown or reversal of this trend in several countries. To distinguish between the large set of proposed explanations, we categorize hypothesized causal factors by whether they accommodate the existence of within-family Flynn effects. Using administrative register data and cognitive ability scores from military conscription data covering three decades of Norwegian birth cohorts (1962–1991), we show that the observed Flynn effect, its turning point, and subsequent decline can all be fully recovered from within-family variation. The analysis controls for all factors shared by siblings and finds no evidence for prominent causal hypotheses of the decline implicating genes and environmental factors that vary between, but not within, families.