Human intelligence has increased to keep pace with improvements in areas such as nutrition, education and health care. However a 2013 study by scholars at the universities of Ulster, UK and Oulu in Finland found a decline in the average IQs of military conscripts on certain tests between 1997 and 2009.
The researchers looked at the average IQs of 25,000 male conscripts between the ages of 18 and 25 between 1988 and 2009. They found that the tests showed increases in scores for three tests (shapes, numbers and words) averaging four IQ points each decade between 1988 and 1997. However the results showed an average decline of two IQ points each decade in all of the tests between 1997 and 2009.
“The decline in the average IQ has been detected in several Nordic countries, Australia, Britain, the United States and the Netherlands,” added Helsinki University assistant professor Markus Jokela.
Jokela stressed that the fall in average intelligence was not dramatic, but was moderate at the level of the wider population.
Researchers have so far not been able settle on a clear explanation for the fall off in intelligence gains. They have considered factors such as lifestyle, health status and culture.
“If we look 30 years backwards at the development of young adults’ health, for at example metabolic risk factors, then there has been a negative development,” Jokela declared.
He pointed out that the so-called Flynn effect - or the long-term increase of average intelligence in many parts of the world during the twentieth century - was due in part to advances in health care, education and nutrition. The negative Flynn effect could also be tied to health status, he noted.
Asked whether or not the proliferation of fragmented information common in the age of the internet could account for the dimming of IQs, Jokela responded,
“It’s a good question – and controversial. We have seen arguments for and against it,” he concluded.
Jokela was also cautious about the long-term impact of popular brain workouts on intelligence. He remarked that such programmes would have to be sustained to see long-term average IQ gains - otherwise, their effects would fade within about one year, he observed.