IQ scores look to be on the decline. Is there a complicated explanation, or are we just getting stupider?

Daniel Engber:

Given all this appetite for news of our destruction, you’d think the Great Endumbening described in that European special would’ve become a source of fascination over here (or at least a source of nervous Facebook posts). Instead, it’s been pretty much invisible. Across the Atlantic, one can find some real concern about a downward slide in measures of intelligence, amid confusing and disturbing arguments over what those changes, if they’re real, could really mean. In the United States, no one seems to care. We might be grateful for this fact—that for whatever reason we’ve been spared another gloom-and-doom prediction. But the latest science about these dropping scores suggests the worries aren’t altogether fake, and that they may deserve more attention than they’ve gotten.

It’s wrong to hint that scores on tests of memory and abstract thinking have been falling everywhere, and in a simple way. But at least in certain countries—notably in Northern Europe—the IQ drops seem very real. Using data from Finland, for example, where men are almost always drafted into military service, whereupon they’re tested for intelligence, Dutton showed that scores began to slide in 1997, a trend that has continued ever since. Similar trends have been documented using data from Denmark, Norway, and Sweden. At some point in the mid-1990s, IQ scores in these countries tipped into decay, losing roughly one-fifth to one-quarter of a point per year. While there isn’t any sign of this effect on U.S. test results (a fact that surely bears on our indifference to the topic), researchers have found hints of something similar in Australia, France, Germany and the Netherlands.

Such signs are all the more surprising given that IQ scores have (or had) been increasing, overall, for many decades in a row. That upward trend was identified by a few different researchers and named for James R. Flynn, who explored it most comprehensively.
Starting in the 1980s, Flynn documented “massive gains” in mean IQ, starting with Americans, whose scores had soared by 14 points since 1932. The Flynn effect has since been well established across at least 34 countries; on average, scholars say IQs have increased by several points per decade.