According to the report, average IQ scores have been dropping since 1975, and initially this was blamed on the fact that clever women were having fewer children.
But new research has suggested that intelligence levels could be dropping simply because people are living longer, and certain types of intelligence decline as after time.
Historically there is evidence that IQ scores improved in wealthy nations for about a century, largely thanks to improvements in living conditions, socially, nutritionally and physically – this was called the Flynn effect – which was first noticed in the 1940s.
But researchers saw what appeared to be a reversal in the trend by about 2004, with IQ scores dropping.
“The drop is around 7 to 10 IQ points percentury,” Michael Woodley of the Free University of Brussels in Belgium, explained.
But Woodley has previously argued that the reason for the decline was because educated people were having fewer children than other social groups.
And it was because of this, he believes, that intelligence levels were dropping globally.
But critics of this view say there is not enough data to back up such a claim.
Researchers went onto to look at the different types of tests used for measuring people’s IQ from 1972, both assessing short-term memory and those that test working memory.
The latter is the ability to retain information for processing, reasoning and decision making – and it is this, the researchers say, that declines with age.
So when they then looked at who was performing the tests, they noticed an increase in the number of people aged 60 or older.
And it could be these people who are seemingly bringing down the overall population IQ scores.
“The idea that population aging may be responsible is interesting and may serve as an alternative to the oft-proposed – but empirically little-supported – selective fertility patterns,” explained Jakob Pietschnig of the University of Vienna in Austria. “It is a novel hypothesis that seems plausible and makes sense.”
But he added that there was insufficient information to draw any definitive conclusions as to why, or if the world’s population were becoming less intelligent.