Cognitive test scores across entire populations have been declining in several wealthy nations after decades of gains — but treating this as a uniform trend may obscure a more troubling reality. New evidence from nearly 600,000 Norwegian men reveals that the so-called Flynn effect reversal is not equally distributed across society, and that the social stratum a person occupies fundamentally shapes whether their cohort's cognitive scores rose, held steady, or fell.
Analyzing mandatory military aptitude data across birth cohorts spanning several decades, researchers found that the well-documented mid-20th-century rise in population IQ scores was disproportionately driven by gains among lower socioeconomic groups — consistent with the idea that expanded access to schooling and nutrition lifted cognitive performance among those previously most disadvantaged. The more recent decline, however, follows a similarly stratified pattern: cognitive scores among men from lower socioeconomic backgrounds have fallen more steeply than among those from higher-status families, even after accounting for educational attainment. The aggregated population trend, it turns out, averages together two very different stories.
This finding carries significant implications for how public health researchers interpret the Flynn reversal. The dominant hypotheses — digital distraction, reduced reading, environmental toxins — tend to assume a uniform exposure. But if the decline is concentrated in lower socioeconomic strata, explanations rooted in inequality and differential access to cognitively stimulating environments become more compelling. The Norwegian military dataset is among the most rigorous available for this kind of generational analysis, offering objective, standardized measurement rather than self-reported proxies. Key limitations include its male-only composition and its restriction to a single high-income Nordic country, which limits generalizability. Still, the stratified pattern is compelling enough to reframe the Flynn reversal as a widening cognitive inequality problem rather than a society-wide cognitive decline — a distinction with profound implications for longevity and healthspan research, given cognition's role in healthy aging outcomes.