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Are Human IQs Falling?
The Flynn Effect and why it may be reversing
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Human IQs were rising globally in the 20th Century, but now some scientists think they are beginning to fall. The rising trend of IQs, known as the Flynn Effect, states that each generation will, on average, score higher on IQ tests than the last. But as we enter the 21st Century, the Flynn effect may be stalling, if not beginning to reverse itself. What does this mean for the future of humanity and progress?
What is the Flynn Effect?
The “Flynn Effect” is an observed rise in intelligence test scores, first documented by researcher and philosopher James Robert Flynn in 1984. Flynn’s initial study calculated an average 13.8-point increase in IQ scores between 1932 and 1978, or about 3 points per decade. While the causes and reasons for the Flynn Effect are the subject of much debate, it is generally accepted that globally, humans scored higher on standardized IQ tests with each passing generation.
For example, if we tested the IQ of a sample of Baby Boomers when they were 20 years old and compared those results to the same test also administered to Millennials at the age of 20, we would expect the latter group’s average IQ scores to be higher. To be clear, none of this is to suggest that younger people are necessarily smarter, but more precisely, that they are scoring better on various standardized tests that measure IQ.
Dozens of subsequent studies have confirmed the Flynn Effect. New calculations of IQ score gains, made between 1972 and 2006, using different versions of the Wechsler Adult Intelligence Scale, Stanford-Binet, and Wechsler Intelligence Scale for Children, indicate an IQ increase of about 0.31 points per year. This finding is broadly consistent with Flynn’s findings in the 1980s.
What Causes the Flynn Effect?
There are multiple proposed causes of the Flynn Effect. Mingroni (2007) hypothesized that IQ gains are the result of increasingly random mating, resulting in what is known as Heterosis or “hybrid vigor.” In other words, changes in social norms, reduced racism, increased migration/immigration, and new technology, brought people with more varied genetic backgrounds together for the first time in human history. While this may explain some of the observed IQ increase, others such as Woodley (2011) have disputed this as a primary cause.
Many researchers have suggested environmental effects as a cause, including sibship size, or the number of siblings one has. In Norway, Sundet et al. found that the greatest increase in IQ scores occurred between cohorts with the largest decrease in sibship size. Other researchers have proposed that improved nutrition, including prenatal and postnatal nutrition, may be partly responsible for the Flynn Effect. This conclusion can be supported by pointing to improvements in other measures of health, including a parallel increase in infants’ head circumference, weight, and height.
Meanwhile, others have suggested improving education as a potential cause, but this seems unlikely. Indeed, when we break down and look at which components of IQ tests are rising the most, we find that the greatest gains are scores for nonverbal performance-based measures, like Raven’s Progressive Matrices. These tests are associated with “fluid intelligence” and not “crystallized intelligence.”
Fluid Intelligence is a measure of an individual's ability to reason abstractly. As I noted in my essay on shrinking and aging populations, Fluid Intelligence peaks around the age of 25. Crystallized Intelligence, on the other hand, is the knowledge that is accumulated and learned over time, and generally peaks around the age of 60. Because the gains are found most prominently in the former and not the latter, the Flynn Effect doesn’t appear to be rooted in better education.
Other more novel causes have been proposed, including the banning of lead-based paint and lead in automobile fuel. There is quite a bit of evidence to suggest that reduced lead concentration in the blood of younger generations has led to a reduced crime rate, but it could only be a partial explanation for rising IQs.
Is the Flynn Effect Reversing?
But before we celebrate the rise of intelligent superhumans, in an odd twist of fate, no sooner did we discover the Flynn Effect, did it begin to slow and stagnate. One meta-analysis of IQ scores across 31 countries from 1909 to 2013, found that the rise of IQ scores for the youngest of cohorts had declined. Many researchers around the world have come to a similar conclusion; the Flynn Effect is stagnating.
In fact, the Flynn Effect may be starting to reverse. Recent studies have found that vocabulary scores fell for the most recent adult samples that were tested between 1974 and 2016; this is happening regardless of educational attainment. Other studies have come to similar conclusions, suggesting that around 1987, gains in crystalized intelligence scores plateaued.
Newer studies have confirmed what appears to be at least a partial reversal of the Flynn Effect in recent years. Indeed, in a large sample study of US adults conducted by Northwestern University, it was found that IQ scores in 3 of 4 key domains dropped from 2006 to 2018, though one key domain, spatial reasoning, continued to rise. This is not an American phenomenon and has been demonstrated in many other countries as well.
The reasons or causes of the reverse Flynn Effect are unclear. Opportunistic types, ironically, have attempted to single out increased immigration as a possible cause, but since younger siblings within the same family and genetic lineage are also showing evidence of falling IQs, this can be ruled out. Instead, the reasons are more likely environmental. Personally, my best guess is the increased proliferation of “junk food” that are both high in calories and deficient in nutrients, which I discussed in detail here, seems a possible cause.
Flynn and Human Progress
From the standpoint of human progress, the Flynn Effect and its potential reversal have profound implications. Indeed, studies have found a positive relationship between the Flynn Effect and economic growth. In one study, researchers examined 28 nations and 262 periods of time between 1909 and 2013. It found that IQ development was correlated to concurrent and/or lagged GDP per capita growth. In other words, cognitive ability contributes to wealth, prosperity, and general human capabilities.
It stands to reason then, that a reversal of the Flynn effect could drag down economic growth, human opportunity, and technological innovation. Such phenomena couldn’t come at a worse time for humanity. Flynn’s reversal is arriving concurrent with shrinking/aging populations and falling research productivity, as I described here. Arresting these declines is critical, and will require smart and difficult policy choices going forward.
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