| Summary: | Background: Understanding the dynamics of the human range expansion across northeastern Eurasia during the late Pleistocene is central to establishing empirical temporal constraints on the colonization of the Americas [1]. Opinions vary widely on how and when the Americas were colonized, with advocates supporting either a pre-[2] or post-[1,3,4,5,6] last glacial maximum (LGM) colonization, via either a land bridge across Beringia [3,4,5], a sea-faring Pacific Rim coastal route [1,3], a trans-Arctic route [4], or a trans-Atlantic oceanic route [5]. Here we analyze a large sample of radiocarbon dates from the northeast Eurasian Upper Paleolithic to identify the origin of this expansion, and estimate the velocity of colonization wave as it moved across northern Eurasia and into the Americas. Methodology/Principal Findings: We use diffusion models [6,7] to quantify these dynamics. Our results show the expansion originated in the Altai region of southern Siberia,46kBP, and from there expanded across northern Eurasia at an average velocity of 0.16 km per year. However, the movement of the colonizing wave was not continuous but underwent three distinct phases: 1) an initial expansion from 47-32k calBP; 2) a hiatus from,32-16k calBP, and 3) a second expansion after the LGM,16k calBP. These results provide archaeological support for the recently proposed three-stage model of the colonization of the Americas [8,9]. Our results falsify the hypothesis of a pre-LGM terrestrial colonization of the Americas and we discuss the importance of these empirical results in the light of alternative models.
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