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Upon crossing the Panamanian Isthmus, it is very unlikely that people migrated directly down the high Andes. In addition to anoxia, the upper Cordillera was glaciated, cold, and sparsely vegetated until the waning of the Ice Age. It is more likely that pioneering groups moved along the continental margins, exploiting the terrestrial and aquatic assets of rivers, deltas, and fresh or salt-water lagoons. Colonization of the Pacific Rim proceeded on a step by step basis, with vanguards moving into a pristine habitat, settling there, and reproducing in growing numbers. Daughter colonies then budded off from the parental hearths to claim fresh homelands and repeat the process. Over the course of multiple generations humans advanced sequentially down the littoral desert, establishing home territories around one and then another river mouth or water source. Costal homesteaders ventured into the lofty sierra to retrieve resources, such as obsidian and game. Yet glaciers, cold and anoxia made the high Cordillera a relatively late frontier of permanent settlement, which awaited the close of the Ice Age. Colonization of the high mountains presumably transpired in a stair step manner, with people acclimatizing to moderate elevations before their altitude-adapted progeny ascended a step further to more lofty habitats

This conjectural colonization scenario has people moving down the continental margin in Pleistocene times along routes now submerged by post-glacial sea-level rise. Still, radiocarbon assays from coastal sites in Peru and Chile confirm that the littoral desert was inhabited by at least 11,500 calendar years ago, and this is a widely accepted base-line for evidence of humans elsewhere in the hemisphere.