Competing chromosomes explain junk DNA.

sciencemag.org SCIENCE Paleoindian, and fishtail points previously provided a roadmap that archaeologists used to trace the spread of Paleoindians throughout the Americas. Such a roadmap is lacking for pre-Clovis sites. Assemblages with distinctive stemmed (“tanged”) chipped-stone projectile points, crescents (lunate-shaped), and leaf-shaped bifaces found in Japan, northeast Asia, western North America, and South America (see the figure) have been proposed as potential markers of a pre-Clovis coastal dispersal (14) that seems generally consistent with genomic data, which suggest a northeast Asian origin for Native American ancestors some time in the past 20,000 years. But more data are needed to close substantial spatial and temporal gaps between these far-flung finds and trace a dispersal route from Asia to the Americas. Work on early coastal localities along the Pacific Coast from Alaska to Baja California (8), Peru (10), and Chile (1) is helping to fill these gaps. If the first Americans followed a coastal route from Asia to the Americas, finding evidence for their earliest settlements will require careful consideration of the effects of sea level rise and coastal landscape evolution on local and regional archaeological records (15). Around the globe, evidence for coastal occupations between ~50,000 and 15,000 years ago are rare because of postglacial sea level rise, marine erosion, and shorelines that have migrated tens or even hundreds of kilometers from their locations at the LGM. Overcoming these obstacles requires interdisciplinary research focused on coastal areas with relatively steep offshore bathymetry, formerly glaciated areas where ancient shorelines have not shifted so dramatically, or the submerged landscapes that are one of the last frontiers for archaeology in the Americas. Methodological and analytical advances are moving us closer than ever toward understanding when, how, and why people first colonized the Americas. Coastal regions are central to this debate. j