Testing the Late Pleistocene Arctic Origins of East Asian Psychology using Ancient and Modern DNA

This study tests climatically driven selection on behavioral polygenic scores (PGS) using global modern genomes together with ancient datasets from both Western and Eastern Eurasia. PGS were computed for Extraversion, Agreeableness, and Neuroticism, and temporal trends were modeled with hinge regressions at 12,000 and 19,000 years BP while adjusting for latitude and coverage. In modern worldwide populations, all three traits showed latitude-associated differentiation, consistent with cold-climate adaptation. In Western Eurasian ancient genomes, Extraversion and Neuroticism both declined with sample age before the Last Glacial Maximum (pre-knot slopes ≈ − 0.018 and − 0.045 to − 0.051 SD/kyr), then reversed direction after 12k–19k BP (slope shifts Δβ ≈ +0.036 to + 0.104, all p < 0.001), indicating post-LGM relaxation of selection. Agreeableness showed the complementary pattern: increasing before the knots and attenuating thereafter. A latent factor extracted from the three traits, oriented to reflect higher Agreeableness and lower Extraversion/Neuroticism, captured these coordinated trends at the population level (Δβ ≈ −0.17, p < 0.001), supporting the single-trait findings. In the Eastern Eurasian sample, limited pre-Holocene coverage precluded hinge tests, but within the Holocene, ancestry components (e.g., Jōmon, Tibetan, Northeast Chinese) predicted trait scores in directions broadly consistent with Arctic adaptation, whereas latitude effects were weaker once admixture was accounted for. Collectively, both trait-specific and factor-level results support the hypothesis that late Pleistocene cold intensified selection against Extraversion and Neuroticism while favoring Agreeableness, with Holocene climates reversing or relaxing these pressures.