ENVIRONMENTAL AND BIOCULTURAL CONSTRAINTS ON THE NORTHWEST COAST ROUTE

Constraints on human dispersal along the Northwest Coast include the paleogeographies of glaciers, sea levels, and ecosystems. There are also several major cultural and biological constraints. Glacier advances and retreats occurred in rough synchrony between Alaska and Puget Sound, but the timing of their maximum extents was out of phase during the last glacial maximum (LGM). Around Kodiak Island, the LGM occurred 21,000-16,000 14C yr B.P. when glaciers flowed to the outer edge of the continental shelf. An interstadial occurred there between ca. 16,000 and 14,000 14C yr B.P. In Puget Sound, the LGM occurred later, around 14,000 14C yr B.P. Few generalizations can be made about sea level history along the NW coast because of complex interactions between tectonics, isostasy, and eustatic sea level. Ecosystem history during the late Pleistocene along the Northwest Coast remains poorly understood. Sizable ice-free areas occurred there intermittently, but no clear evidence exists to indicate whether these ice-free areas comprised refugia supporting abundant or diverse biota. From population biology and from the archaeological records of sea-going Thule, Lapita, and Polynesian peoples, we can infer something about the cultural and biological challenges posed by maritime dispersals. The paramount danger is the Allee effect, the risk that a small group will go extinct through chance events even if birth rates are maintained at the same levels that would allow population growth in more populous settings. Combined with this is a technological Allee effect involving the accidental loss of information when population sizes fall too low. As a final note, geological data can narrow the search for the archaeological remains of maritime people entering the Americas. On unglaciated coasts, post-glacial sea-level rise has drowned ancient shorelines except in areas where rapid tectonic uplift outstripped the rising water. Rapid, long-term tectonic uplift occurs in two geological settings. The first is located under the continental margin of Central and South America, where large igneous provinces are being subducted. The second occurs alongside major transverse fault systems along the west coast of North America.