IT TOOK just eight years for us to put a man on the moon after US president John F. Kennedy made the bold declaration in 1961 — and this was done in a time before email was even invented.

Humans are capable of some astounding feats, evidenced by the scientific and technological achievements of the 20th century. But have we peaked?

New research suggests we have.

Since the Second World War, the IQ of young people was observed to be steadily rising. Dubbed the Flynn effect — named after the work of New Zealand intelligence researcher James Flynn — it described a phenomenon in which humans’ intelligence quotient was rising at a rate of about three IQ points per decade in the 20th century.

However, that has been shown to have topped out around 1975 with IQ scores now falling. “Recent years have seen a slowdown or reversal of this trend in several countries,” researchers wrote in a new paper, published this week in the Proceedings of the National Academy of Sciences.

There are plenty of different factors that could explain the so-called reverse of the Flynn effect including a change in the way we teach math, science and language or perhaps it’s because changes in human intelligence in the digital world are not best captured by traditional IQ tests.

Scientists in Norway recently set out to understand what could explain why we don’t test as high as those born nearly 50 years ago.

Researchers from the Ragnar Frisch Centre for Economic Research in the country analysed some 730,000 IQ test scores of 18 to 19-year-old Norwegian men who took the tests as part of their compulsory military service.

The tests took place between 1970 and 2009 and showed a turning point for the Flynn effect occurred for the post-1975 birth cohorts, amounting to seven fewer IQ points per generation, researchers said.

Those born in 1991 scored about five points lower than those born in 1975, and three points lower than those born in 1962.

While it’s important not to draw too broad or concrete conclusions from such analysis, one expert labelled the findings “worrying”.

“This is the most convincing evidence yet of a reversal of the Flynn effect,” psychologist Stuart Ritchie from the University of Edinburgh, who was not involved in the study, told The Times newspaper in the UK.

“If you assume their model is correct, the results are impressive, and pretty worrying.”

If I read this correctly, people born in the early 1970s are the smartest generation in history. I always suspected as much.https://t.co/HSvWMV3jf2 — Tim Harford (@TimHarford) June 13, 2018

The Norwegian researchers hypothesised that the observed change was due to environmental factors rather than family factors.

“Using administrative register data with information on family relationships and cognitive ability for three decades of Norwegian male birth cohorts, we show that the increase, turning point, and decline of the Flynn effect can be recovered from within-family variation in intelligence scores,” the researcher wrote.

“This establishes that the large changes in average cohort intelligence reflect environmental factors and not changing composition of parents, which in turn rules out several prominent hypotheses for retrograde Flynn effects.”