The co-evolution of genes, diet, and dental traits provides critical insights into human adaptation during the Late Pleistocene. Here, we propose a three-dimensional coupled model linking aquatic protein-rich nutritional substrate, the EDAR V370A functional-enhancing variant, and the shovel-shaped incisor phenotype in ancient populations of northern China. High-quality ancient DNA evidence from Tianyuandong and other key sites confirms the early presence of EDAR V370A in Northeast Asian populations, while paleoenvironmental data (e.g., Bohai Bay sediment cores, pollen records) indicates prolonged coastal and wetland habitats with abundant aquatic resources during Marine Isotope Stage 3. We hypothesize that long-term consumption of aquatic proteins (fish, shellfish, and aquatic lipids) served as an energy buffer and nutritional foundation, facilitating the positive selection of EDAR V370A, which in turn contributed to the high prevalence of shovel incisors in East Asians. This model integrates genetic, dental, and paleoenvironmental lines of evidence, offering a local, multi-regional evolutionary perspective distinct from simple out-of-Africa scenarios. It further highlights the role of aquatic resource exploitation as a key adaptive strategy in Late Pleistocene East Asian populations.