Comparative morphological studies of the earliest human skeletons of the New World have shown that, whereas late prehistoric, recent, and present Native Americans tend to exhibit a cranial morphology similar to late and modern Northern Asians (short and wide neurocrania; high, orthognatic and broad faces; and relatively high and narrow orbits and noses), the earliest South Americans tend to be more similar to present Australians, Melanesians, and Sub-Saharan Africans (narrow and long neurocrania; prognatic, low faces; and relatively low and broad orbits and noses). However, most of the previous studies of early American human remains were based on small cranial samples. Herein we compare the largest sample of early American skulls ever studied (81 skulls of the Lagoa Santa region) with worldwide data sets representing global morphological variation in humans, through three different multivariate analyses. The results obtained from all multivariate analyses confirm a close morphological affinity between SouthAmerican Paleoindians and extant Australo-Melanesians groups, supporting the hypothesis that two distinct biological populations could have colonized the New World in the Pleistocene͞Holocene transition.Paleoamericans ͉ Paleoindian morphology ͉ Paleoindians

The peopling of the New World has been the focus of anthropological attention since the last century. Proponents of multiple migration models have claimed that patterns of variation among extant New World populations reflect ancient, discrete migrations to the Americas during the terminal Pleistocene. Although multiple migration models appear to explain patterns of both past and present craniometric variation, this interpretation rests on a number of key assumptions that require further investigation. We examined a series of Paleoindian (n ϭ 11) and Archaic (n ϭ 384) crania from North and South America, and compare these early samples to a large worldwide sample of late Holocene (n ϭ 6,742) remains to assess within-and among-group variability in early samples, and to determine how patterns of variation could be viewed as a reflection of both population history and population structure. Analyses included univariate and multivariate analysis of variance, principal component analysis, calculation of biological distances, and multivariate allocation methods. We also performed model-bound analyses of these data, including Relethford-Blangero analysis and calculation of F ST . Our results indicate that under the assumptions of migration/founder models, the data are consistent with Paleoindians having derived from an undifferentiated Asian population that was not ancestral to modern American Indians. This view can be accommodated into existing models of multiple founders (migrations) in the New World. However, the assumptions required for such an interpretation are not realistic, and the diversity of early populations could as easily reflect population structuring processes such as genetic drift, demographic growth, and other phenomena. When the data were analyzed controlling for the effects of genetic drift (i.e., with smaller long-term effective population sizes for Paleoindians), the Paleoindian samples were no longer distinct from modern Native American populations. Other factors that need to be considered include processes involved in craniofacial change and adaptation during the past 10,000 years. Finally, patterns of variation in the North and South American Paleoindian samples are different, suggesting that the process of New World colonization is more complex than previously assumed.

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BackgroundDiscussion surrounding the settlement of the New World has recently gained momentum with advances in molecular biology, archaeology and bioanthropology. Recent evidence from these diverse fields is found to support different colonization scenarios. The currently available genetic evidence suggests a “single migration” model, in which both early and later Native American groups derive from one expansion event into the continent. In contrast, the pronounced anatomical differences between early and late Native American populations have led others to propose more complex scenarios, involving separate colonization events of the New World and a distinct origin for these groups.Methodology/Principal FindingsUsing large samples of Early American crania, we: 1) calculated the rate of morphological differentiation between Early and Late American samples under three different time divergence assumptions, and compared our findings to the predicted morphological differentiation under neutral conditions in each case; and 2) further tested three dispersal scenarios for the colonization of the New World by comparing the morphological distances among early and late Amerindians, East Asians, Australo-Melanesians and early modern humans from Asia to geographical distances associated with each dispersion model. Results indicate that the assumption of a last shared common ancestor outside the continent better explains the observed morphological differences between early and late American groups. This result is corroborated by our finding that a model comprising two Asian waves of migration coming through Bering into the Americas fits the cranial anatomical evidence best, especially when the effects of diversifying selection to climate are taken into account.ConclusionsWe conclude that the morphological diversity documented through time in the New World is best accounted for by a model postulating two waves of human expansion into the continent originating in East Asia and entering through Beringia.

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