The Latitude Differentiation Model: A Unified Framework for Local Evolution in Eurasia

The Recent African Origin (RAO) paradigm has long dominated narratives of human evolutionary origins, depicting anatomically modern Homo sapiens as originating in Africa approximately 60,000 years ago, followed by complete demographic replacement of all indigenous archaic populations across Eurasia. Over the past fifteen years, however, converging interdisciplinary evidence from ancient genomics, paleomorphology, fossil chronology and population genetics has generated three robust empirical observations that the classic RAO model cannot coherently accommodate: European context: Neanderthals display more than 400,000 years of in-situ evolutionary continuity, evolving gradually from Homo heidelbergensis. Their diagnostic morphological traits—including mid-facial prognathism, occipital torus development and specialized nasal architecture—represent long-term adaptive shaping under high-latitude cold-climate selective pressures. East Asian context: Shovel-shaped incisor morphology exhibits unbroken morphological continuity, traceable from Middle Pleistocene Homo erectus at Zhoukoudian (~500 ka), through early archaic Homo sapiens at Xujiayao (~100 ka), to Late Pleistocene modern humans at Upper Cave (~30 ka). The extremely high prevalence of this trait in northern East Asian populations cannot be explained merely by genetic drift. Genetic introgression: Non-African modern populations retain 1–4% Neanderthal-derived ancestry, with introgressed genomic segments significantly enriched in loci associated with immune function, skin pigmentation, hair follicle development and energy metabolism—clear signatures of adaptive introgression rather than neutral retention. Studies published 2024–2025 further confirm that archaic-modern gene flow was bidirectional, demographically asymmetric, and sustained over millennia, rather than occurring as a single isolated admixture event. This study proposes the Latitude Differentiation Model as a competing synthetic framework. On million-year evolutionary timescales, the unique selective regime of high-latitude Eurasia (north of 40°N)—characterized by cold stress, aridification and strong seasonal resource fluctuation—drove convergent adaptive evolution of shared morphological and physiological traits in geographically isolated regional populations. Such derived characteristics are neither inherited African plesiomorphic features nor random products of genetic drift, but environmentally canalized parallel adaptations. Taking European Neanderthal evolution and East Asian shovel-shaped incisor diversification as paired case studies, this paper demonstrates that in-situ morphological continuity, inter-population genetic admixture and adaptive archaic introgression collectively invalidate the strict “complete replacement” hypothesis. We further advocate the establishment of a Eurasian cross-regional comparative research network, repositioning high-latitude zones as autonomous engines of local evolutionary innovation, rather than passive recipients of African-derived genetic heritage.