Why did behavioral modernity emerge in the mid-latitudes rather than the tropical cradle of humanity? The main paper proposes the Mid-Latitude Seasonal Oscillation Hypothesis, arguing that millennial-scale climate fluctuations across the Northern Hemisphere 35°–40°N belt during the Last Glacial period acted as the core selective regime driving behavioral modernity. This hypothesis is empirically falsifiable: it would be disproven if continuous archaeological records of behavioral modernity from regions outside the 35°–40°N belt (e.g., low-latitude Africa) can be reliably dated to an earlier period than the oldest evidence from East Asian mid-latitude refugia, provided that “continuous” is defined as at least three archaeological sites spanning ≥5,000 years. The hypothesis focuses on the primary origin and sustained development of behavioral modernity, rather than sporadic or later dispersal of related traits across other regions. As a companion piece, this study does not reiterate the paleoclimatic and archaeological evidence detailed in the main text. Instead, it delivers three independent, cross-domain verifications. First, a low-latitude counter-proof: genomic analyses of the San and Central African Pygmies (Fan et al., 2023) reveal tens of millennia of morphological and cultural stasis under equatorial constant-temperature conditions, demonstrating that without oscillation, there is no innovation. This inference applies specifically to thermally stable low-latitude environments; the possible convergent evolution in the Southern Hemisphere mid-latitudes (e.g., southern Africa ~35°S) does not challenge the Northern Hemisphere origin priority, which awaits independent chronological testing. Second, cross-domain convergence: the latitudinal cline of skin pigmentation genes (e.g., OCA2) shows that latitude operates as an overlapping field of multiple selective pressures—UV intensity, cold stress, and vitamin D metabolism—thereby framing the mid-latitudes as a high-pressure selective zone. Although pigmentation genes do not directly encode behavioral traits, this multi-pressure overlap demonstrates that mid-latitude populations simultaneously faced selective forces acting on metabolism, neurodevelopment, and stress response—a population genetic precondition that accelerated the accumulation of cognitive and behavioral innovations. Third, a molecular anchor: integrating the post-LGM positive selection signal of EDAR V370A (Mao et al., 2021) with its pleiotropic functional validation (Kamberov et al., 2013) upgrades the shovel-shaped incisor from a “neutral drift marker” to a fossil fingerprint of cold/oscillation adaptation. While this selection signal emerged after the Last Glacial Maximum rather than during the main phase of millennial-scale oscillations (75–15 ka), it nonetheless validates the core causal chain—environmental oscillation → adaptive selection → phenotypic signature—and extends its temporal relevance into the post-LGM period. Together, these lines of evidence converge on a single principle: latitude is not merely a spatial coordinate, but a switch of evolutionary regimes. The mid-latitude oscillation belt functioned as the primary crucible of behavioral modernity. Significance Statement The classic “Out of Africa” model fails to explain why behavioral modernity arose in climatically volatile mid-latitudes, instead of humanity’s tropical homeland. Here we test the Mid-Latitude Seasonal Oscillation Hypothesis via three cross-domain approaches. We demonstrate that equatorial populations including the San and Pygmies were trapped in evolutionary stasis under stable thermal environments; that pigmentation genes (OCA2) reveal mid-latitudes as a multi-pressure selective arena; and that East Asian shovel-shaped incisors, linked to the positively selected EDAR V370A variant, are not products of neutral drift but phenotypic traces of adaptation to climatic oscillation. We conclude that latitude functions as an evolutionary regime switch: sustained environmental oscillation is a prerequisite for evolutionary and cultural innovation.
Jing Zhang (2026) studied this question.