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Evidence: High-IQ individuals show delayed cortical thickening (up to age 13 vs. 8 in average IQ), allowing extended plasticity. Shaw et al. (2006) found superior IQ correlates with prolonged prefrontal cortex growth, a neotenous marker.
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Evolutionary link: Neoteny enabled bigger brains (humans have 3x primate average), correlating with IQ (r=0.40 via MRI). Transgenic studies (e.g., MCPH1 gene in monkeys) induce human-like neoteny, boosting cognitive performance.
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Group patterns: Populations with higher average IQ (e.g., Ashkenazi Jews ~110-115) exhibit neotenous features like extended education phases, aligning with selection for cognitive traits.
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Evidence of reversal: Prewar, IQ gaps were attributed to genes (e.g., Brigham’s 1923 army tests). Postwar, critiques (e.g., Klineberg 1935) highlighted migration/environment effects; Flynn effect (3-point/decade rise) undermined fixed heritability.
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Exaggeration of equality: Hereditarians like Jensen (1969) argued postwar “blank slate” ideology ignored data, using edge cases (e.g., high-IQ minorities) to flatten distributions. Surveys show 45% of experts attribute Black-White gaps to genes+environment, but public discourse emphasizes equality.
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Critiques: Nisbett (2009) claims environmental factors explain all gaps; Rushton & Jensen (2005) counter with admixture studies showing genetic gradients. The shift is seen as ideological (e.g., avoiding eugenics stigma), but data like twin studies (h^2=0.8) challenge pure environmentalism.