Testing evolutionary and dispersion scenarios for the settlement of the new world - PubMed (original) (raw)

Testing evolutionary and dispersion scenarios for the settlement of the new world

Mark Hubbe et al. PLoS One. 2010.

Abstract

Background: Discussion 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 findings: USING 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.

Conclusions: We 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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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1

Figure 1. Representation of the geographic dispersion models tested for the occupation of the Americas.

Model 1 is not represented because it is a control model (assuming direct linear distances among all groups). The bars represent the morphological change observed in East Asia (left) and America (right) during Late Pleistocene/Early Holocene. The red color represents the morphology present in Asia by the end of the Pleistocene and the blue color represents the morphology present nowadays in Asia and America. Model 2 assumes that the morphological differentiation in East Asia occurred before America's settlement and that the New World was occupied only once; Model 3 assumes two distinct dispersions into the continent. See text for detailed description of each model. The dates presented are just approximations, but they assume America's settlement to have occurred around 15 kyr BP (19–22).

Figure 2

Figure 2. Minimum Spanning Tree of the series calculated from the Mahalanobis squared distances among groups and plotted over their geographic coordinates.

The lines represent the closest path for connecting all samples according to the morphological distances between them. Red dots represent samples with Paleoamerican morphology and the brown dot represents the specimens from Zhoukoudian Upper Cave. Blue dots indicate the Late Holocene samples from East Asia, the Americas and Australo-Melanesia.

Figure 3

Figure 3. Boxplot of the pairwise mean rates of morphological differentiation (gray dots) calculated between Paleoamerican and Amerindian series.

The black squares represent the average of the pairwise mean rates for each scenario and the rectangle represents the confidence limit defined by one time the standard deviation of the mean rates. The black horizontal line shows the upper limit of the neutral expectation range (0.01). A) Results for the 24 variables set. B) Results for the 19 variables set.

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