For most of the twentieth century, humanity was getting measurably smarter. Generation after generation scored higher on IQ tests than the one before. Researchers confirmed the trend so consistently that it earned its own name: the Flynn Effect, after the New Zealand intelligence researcher James Flynn (1934–2020), who documented it across dozens of countries. Average IQ rose by roughly two to three points per decade — a modest annual change that, compounded over a century, amounted to a dramatic collective shift in measured cognitive ability.
Then, around the turn of the millennium, the rise stopped. In many developed countries, it reversed.
This reversal — the Reverse Flynn Effect — has now been documented across multiple countries by independent research teams. The evidence points to an uncomfortable conclusion: for the first time in recorded history, younger generations in the developed world are scoring lower on cognitive tests than their parents did at the same age. Gen Z appears to be the first generation to fall below the preceding one on IQ metrics, breaking a trend that had held for over a century.
The Numbers That Started the Alarm
The clearest early evidence came from Norway in 2018, when researchers Bernt Bratsberg and Ole Rogeberg analysed IQ data from over 730,000 men who had undergone mandatory military conscription testing between 1962 and 1991. They found a clear decline in scores among men born after 1975. Their methodological masterstroke was comparing brothers from the same families — which allowed them to rule out genetic explanations entirely. Both the rise and the fall, they concluded, were caused by the world people grew up in, not the genes they inherited. (Proceedings of the National Academy of Sciences, 2018)
The findings were far from isolated. A 2024 study tracking German-speaking populations from 2005 to 2024 found a decline in figural reasoning — a core measure of fluid intelligence — of between 4.68 and 5.17 IQ points per decade, almost as steep as the historical rate of increase. In the United States, the Flynn Effect had slowed to around 1.2 IQ points per decade by 2024, well below the expected three, with outright declines in verbal comprehension and working memory. James Flynn himself had observed the pattern before his death: the average British 14-year-old lost roughly two IQ points over 28 years, with middle-class children losing as many as six.
What is not declining is spatial reasoning, which appears to have improved — possibly due to video games and visual digital environments. What is clearly falling is fluid intelligence: abstract reasoning, sustained attention, the ability to solve novel problems. These are the capacities that education is supposed to build and that science and innovation most depend on.
Screens, Scrolling and the Brain Rot Generation
The Norwegian researchers pointed to three culprits: declining educational quality, increased media exposure, and poor nutrition. Of these, the media story has become the most visible and the most contested.
The rise of short-form, algorithmically curated content — YouTube, Instagram, TikTok — has fundamentally altered how young people spend their cognitive time. Research in 2024 and 2025 linked heavy social media use to shortened attention spans, weakened working memory, and a measurable shift away from deep comprehension toward rapid scanning. Oxford University Press named “brain rot” its Word of the Year for 2024, after the term’s usage surged by 230 percent in a single year. The phrase, originally coined by Thoreau in 1854 to describe declining intellectual standards, has found a jarring contemporary relevance.
The classroom has not been spared. Neuroscientist Jared Cooney Horvath and others have argued that the wholesale digital transformation of schools — tablets, cloud platforms, constant connectivity — has rewarded short-term recall over sustained reasoning and quietly eroded the effortful cognitive engagement that builds general intelligence. Comparative data from dozens of countries show the same pattern wherever digital technology became deeply embedded in schools during the 2010s.
The Poison That Stole a Century of IQ Points
One of the least-discussed chapters in this story involves lead. For decades, leaded petrol and lead-based paint exposed entire populations — especially children — to a neurotoxin now known to cause lasting neurological damage at even very low concentrations. Studies in Environmental Health Perspectives confirmed there is no safe level of lead exposure for a developing brain.
The phased elimination of lead from petrol and paint across Europe and North America from the 1970s onward is now credited with generating a meaningful portion of the Flynn Effect’s gains. One analysis estimated that reductions in US lead exposure between the late 1970s and mid-2000s effectively saved more than 100 million IQ points across the population. A 2024 review from the National Institute of Environmental Health Sciences confirmed that lead and organophosphate pesticides continue to suppress IQ in children in areas with older housing and industrial pollution — a reminder that the environmental story is not yet over.
Outsourcing Thought to Machines
The most recent and perhaps most consequential development involves artificial intelligence. A 2025 study by Michael Gerlich, published in the journal Societies, surveyed 666 participants and found a significant negative correlation between frequent AI tool usage and critical thinking ability. The mechanism was cognitive offloading — the more participants relied on AI systems to reason and decide on their behalf, the worse they performed on independent assessments of critical reasoning. Younger participants showed the highest AI dependence and the lowest critical thinking scores. (Societies, 15(1), 2025)
The concern is not that AI is uniformly harmful. Moderate use, as a scaffold for learning, can be beneficial. The problem is unreflective dependence — allowing AI to perform the effortful cognitive work that, without practice, atrophies. The analogy with physical fitness holds: a muscle unused weakens. If AI routinely does the hard thinking, the neural pathways that support independent reasoning may gradually diminish through disuse.
A Warning the Data Cannot Make Any Clearer
The Reverse Flynn Effect is not a hypothesis. It is a documented reality that has survived peer review across multiple countries and methodologies. The cognitive capacities most associated with deep, flexible, original thinking are declining in the world’s most developed societies — while continuing to rise in much of the developing world, where the historical conditions that once drove Western IQ gains are only now taking hold.
The same environmental plasticity that allowed IQ to rise for a century can, in principle, be harnessed to reverse the decline. Reading long-form texts, physical exercise, reduced early screen exposure, cleaner environments, and a more intentional relationship with AI all have evidence behind them. Several Scandinavian countries have already begun rolling back digital classrooms and returning to printed textbooks.
Whether any of this happens at scale — against the commercial incentives of the attention economy and the institutional inertia of education systems already committed to screens — is a political question as much as a scientific one. The evidence is in. The question now is whether we are still sharp enough to act on it.
Sources:
Bratsberg, B., & Rogeberg, O. (2018). Flynn effect and its reversal are both environmentally caused. PNAS, 115(26). https://doi.org/10.1073/pnas.1718793115
Dierckx, B., & Hoorelbeke, K. (2024). Measurement-invariant fluid anti-Flynn effects in German student samples (2012–2022). Intelligence. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10816863/
Oberleiter, S., et al. (2024). Flynn effect and decreasing positive manifold strengths in Austria (2005–2018). Journal of Intelligence. https://pmc.ncbi.nlm.nih.gov/articles/PMC11676032/
Gerlich, M. (2025). AI tools in society: Impacts on cognitive offloading and critical thinking. Societies, 15(1), 6. https://doi.org/10.3390/soc15010006
Grandjean, P. (2012). Brain tax: Environmental chemicals and IQ loss. PLOS Medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3339482/
Wikipedia: Flynn Effect. https://en.wikipedia.org/wiki/Flynn_effect
The Quantum Record (2025). Global IQ decline and the rise of AI-assisted thinking. https://thequantumrecord.com/philosophy-of-technology/global-iq-decline-rise-of-ai-assisted-thinking/
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