Science

The Great Endumbening

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

Photo illustration of a brain inside a human head. Maybe it is smarter now, maybe it is dumber. Who's to say?
Photo illustration by Slate. Photos by Thinkstock.

In November, the European TV channel Arte aired an hourlong documentary, Demain, tous crétins?Tomorrow, everyone’s an idiot?—on a topic that would seem to be of great importance. It starts with a London-based researcher, Edward Dutton, who has documented decades-long declines in average IQs across several Western countries, including France and Germany. “We are becoming stupider,” announces Dutton at the program’s start. “This is happening. It’s not going to go away, and we have to try to think about what we’re going to do about it.”

The same documentary has also been released in the U.S., with the less provocative title Brains in Danger?. (It’s now available for streaming on Amazon Prime.) American consumers have long shown interest in the claim that our mental skills are shrinking over time, from the internet or phones or television; from having sex or not having sex; from eating vegetables or getting fat; or from whatever other ills of modern life happen to be on our minds. We’re just as drawn to other signs and symptoms of human degeneration, as expressed in trendlines pointing straight to hell. The latest example of this genre came out just last week in the form a much-shared feature story from GQ, on the gradual diminution of Western men and Western semen, toward a forecast state of “Sperm Count Zero”—that is, a world in which there are “no more naturally conceived babies and potentially … no babies at all.”

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.

That scores could rise so quickly and pervasively cast doubt on racist claims about IQ, in particular the idea that racial testing gaps in the U.S. were genetically determined. Changes in the way that people lived, at least in wealthy countries—more widespread and better education, smaller families with greater focus given to each child, superior healthcare and nutrition—appeared to make them test as smarter over time. Flynn also argued that the rise in scores reflected major changes in how we spent our time, and the sorts of problems we had to solve. It wasn’t that our great-grandparents were less intellectually adept than we are. Rather, they possessed different “habits of mind,” and less of an inclination to think in (more test-friendly) terms of abstract logic and hypotheticals.

The existence of the Flynn effect also posed a challenge to the idea—already well-established in certain quarters—that people must be getting dumber over time. According to that theory, called “dysgenics,” people with more intelligence will spend more years in school, on average, and this extra time spent on education correlates with having fewer babies. Therefore, this argument goes, the genes for having high IQ will tend to shrink in prevalence within a population. (This is more or less the plot of the 2006 comedy Idiocracy; in fact, a 35-second clip from that film appears at the start of the European documentary.)

So how do dysgenic theorists explain the fact that IQ scores were going up instead of down? They argued that two forces must be acting at the same time, and in opposite directions: a gentle and genetic push toward lower scores, splashing up against a tidal boost from the environment.

If that’s true, then an “Anti-Flynn effect” would make sense. It may be that we’ve topped out on raising test scores through better schooling and nutrition, or any of the other social factors that supported earlier gains in average IQ. Once those benefits were fully realized, the dysgenicists argue, the Flynn effect would level off—and then the underlying and genetic downward trend could take over. That appears to be Edward Dutton’s view, though other scholars who’ve been studying the same effect say the drops are best explained by rising levels of immigration.

Both those explanations should raise some bright-red flags. Indeed, racists and cranks seem especially interested in proposing theories for the IQ score decline, and their arguments stink of white supremacy. A survey of 75 “experts in cognitive ability research,” published last year, asked respondents to evaluate nine possible causes of the Anti-Flynn effect. The two they rated as the most important were “low intelligent adults have more children than others” and “migration.” (“Worse education and school systems” ranked in the middle of the list; “worse health” was at the bottom.) In Demain, tous crétins?, Dutton warns that, should such factors be left unchecked, “civilization will go into reverse.” To illustrate this not-so-coded threat, the filmmakers have him pull a wooden toy block from the bottom of a tower, leading to its collapse. The next scene begins with the sound of a mournful Bach partita for the solo violin.

In the absence of comprehensive or convincing data on the scope or cause of this IQ decline, the patchy science of this trend has been embroidered with an ugly racist fringe. But a study out last June from scientists in Norway has done a lot to clarify—and detoxify—the issue. Bernt Bratsberg and Ole Rogeberg looked at military records (akin to those that Dutton used for Finland) for more than 700,000 recruits dating back to the 1970s. The researchers focused on pairs of brothers, looking to see if any long-term trends—an upwards-acting Flynn effect, or a downwards-acting Anti-Flynn effect—could be observed within each family, taking hold in the years between each sibling’s birth.

What they found is that for Norwegians born between 1962 and 1975, IQs increased within each family by 0.26 points per year: Younger brothers had slightly higher scores than their older siblings, relative to expectations. (The researchers had to control for the more general fact that older siblings tend to have higher IQs than younger ones.) From 1975 until 1991, this tendency reversed, with test scores dropping by 0.33 points per year within each family.

If it were really true that the anti-Flynn effect resulted from an Idiocracy scenario, in which the most intelligent people have the fewest kids, then IQs should not decline from one Norwegian to his younger brother (since their parents are the same). Rather, the downward trend in average scores would show up as an average across families; there would be, in total, fewer kids from homes where everyone is gifted, and more from homes where everyone is not. The same logic applies to the claim that immigrants changed the gene pool in a way that lowers overall IQs. In other words, Bratsberg and Rogeberg showed that the anti-Flynn effect does not substantially result from immigration or dysgenics—but rather stems from some broad, environmental factor.

What could be endumbening Norwegians, then? The authors note several possible factors, among them worsening health and nutrition, a decline in the quality of education, detrimental changes to media exposure, and the indirect effects of immigration. They fail to mention another substantive hypothesis: that the IQ decline might be caused by chemical pollutants.

That’s the theory posed by Paris-based endocrinologist Barbara Demeneix. In her 2017 book from Oxford University Press, Toxic Cocktail: How Chemical Pollution Is Poisoning Our Brains, Demeneix argued that hormone-twisting industrial poisons have so interfered with human thyroid function that the species has been thrust into “a sort of brain evolution in rather rapid reverse”—which includes among its symptoms, she says, the gradual diminishment of the human intellect, and increasing rates of autism and ADHD.

Demeneix is the star of Demain, tous crétins? (She’s also the one who plays that Bach partita on the violin.) The film lays out her argument in great detail, stressing how iodine deficiencies, along with the spread of flame retardants, pesticides, PCBs, plastic residues, and other filth may be changing people’s brains. The GQ story on the sperm decline points to the same set of endocrine-disrupting, civilization-destroying chemicals, and it’s worth noting that the co-directors of the IQ documentary put out another film in 2008 about how such chemicals might be affecting global testicles.

The drops in sperm count and IQ have a fair amount in common, as it happens. For both phenomena, there’s been an urge to pin the blame on toxic chemicals (at least in media accounts), while ignoring other causes. It may well be that sperm declines are linked, in part, to phthalates leeched from plastic packaging, but they could also be induced by lousy diets and obesity, or too much time spent sitting down, or even global warming. As for the anti-Flynn effect, a focus on endocrine-disrupting chemicals may obscure other, more important social factors. Flynn himself suggested, in a recent paper with his colleague Michael Shayer, that the IQ drop may reflect a rise in service-sector jobs, and a resulting shift towards work that doesn’t foster abstract thought. “During the 20th century, society escalated its skill demands and IQ rose,” they wrote. “During the 21st century, if society reduces its skill demands, IQ will fall.’

Also, both the sperm-count drop and IQ decline have been studied most conclusively in Scandinavia, and the effects could be most severe in Northern Europe. According to the numbers, the Great Endumbening isn’t merely absent here in North America; our test results suggest that, by and large, Americans’ IQs are still increasing. That’s despite our suffering just as much, or even more, than Europeans from the dulling plagues of screen time, processed food, and chemical contaminants. If we’ve got all the same environmental factors as the Finns and the Norwegians, and still we’re getting smarter every year, then what’s the point of worrying?

As Flynn and Shayer note, Scandinavian IQ declines might well presage future trends in other countries. It may be that, once we’ve made our schools as good as theirs, we’ll see our Flynn effect max out, and then whatever channels feed their anti-Flynn effect will show up in our data, too. While this wouldn’t mean civilization has gone into reverse—we may have made that turn already, steered by something other than IQ—I think it would be smart to study why it’s happening.