Testing Evolutionary and Dispersion Scenarios for the Settlement of the New World

Instituto de Investigaciones Arqueológicas y Museo, Universidad Católica del Norte, San Pedro de Atacama, Chile.
PLoS ONE (Impact Factor: 3.23). 06/2010; 5(6):e11105. DOI: 10.1371/journal.pone.0011105
Source: PubMed


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.
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.
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.


Available from: Katerina Harvati
    • "Using a linear model to control for one variable has another limitation which is the inherent risk of removing some genetic differences together with climate effects. While other studies advocate removing some morphometric variables (e.g., Hubbe et al., 2010) or groups (e.g., Reyes-Centeno et al., 2015 ) prone to be more influenced by adaptation, this approach offers the advantage of keeping all morphometric variables and all populations, while allowing the comparison of climate-corrected results with non-corrected results. Previous studies were based on linear distances (Alsup, 2012; Hubbe et al., 2010 Hubbe et al., , 2011), or 2D landmarks (de Azevedo et al., 2011), whereas we use 3D geometric morphometrics, which brings the full geometry of the skull to the analyses. "
    [Show abstract] [Hide abstract] ABSTRACT: Objectives: Craniofacial variation in past and present Amerindians has been attributed to the effect of multiple founder events, or to one major migration followed by in situ differentiation and possibly recurrent contacts among Circum-Arctic groups. Our study aims to: (i) detect morphological differences that may indicate several migrations; (ii) test for the presence of genetic isolation; and (iii) test the correlation between shape data and competing settlement hypotheses by taking into account geography, chronology, climate effects, the presence of genetic isolation and recurrent gene flow. Methods: We analyzed a large sample of three-dimensional (3D) cranial surface scans (803 specimens) including past and modern groups from America and Australasia. Shape variation was investigated using geometric morphometrics. Differential external gene flow was evaluated by applying genetic concepts to morphometric data (Relethford-Blangero approach). Settlement hypotheses were tested using a matrix correlation approach (Mantel tests). Results: Our results highlight the strong dichotomy between Circum-Arctic and continental Amerindians as well as the impact of climate adaptation, and possibly recurrent gene flow in the Circum-Arctic area. There is also evidence for the impact of genetic isolation on phenetic variation in Baja California. Several settlement hypotheses are correlated with our data. Conclusions: The three approaches used in this study highlight the importance of local processes especially in Baja California, and caution against the use of overly simplistic models when searching for the number of migration events. The results stress the complexity of the settlement of the Americas as well as the mosaic nature of the processes involved in this process. Am. J. Hum. Biol., 2016. © 2016 Wiley Periodicals, Inc.
    No preview · Article · Feb 2016 · American Journal of Human Biology
    • "Nevertheless, including fossils with skeletal data of extant human populations will also continue to be important for developing a coherent theory of modern human origins and dispersal (e.g. Hubbe et al., 2010; Pinhasi and von Cramon- Taubadel, 2009; Reyes-Centeno et al., 2015). Comparative morphological approaches have been useful in paleoanthropology, but the discipline will excel further by continuing to develop methods founded in evolutionary theory, such as has been productively done in employing quantitative genetic approaches (Roseman and Weaver, 2007; von Cramon-Taubadel, 2014; Weaver, 2014). "
    [Show abstract] [Hide abstract] ABSTRACT: Genetic and fossil evidence has accumulated in support of an African origin for modern humans. Despite this consensus, several questions remain with regard to the mode and timing of dispersal out of the continent. Competing models differ primarily by the number of dispersals, their geographic route, and the extent to which expanding modern humans interacted with other hominins. Central in this debate is whether Southeast Asia was occupied significantly earlier than other parts of Eurasia and, if so, whether the population ancestral to extant Southeast Asians was notably different from the ancestors of extant Eurasians. Here, genetic and fossil evidence for the dispersal process out of Africa and into Asia is reviewed. A scenario that can resolve the current archaeological, genetic, and paleontological evidence is one which considers an initial expansion of anatomically modern humans into the Arabian Peninsula and the Levant during the terminal Middle Pleistocene, with continued exchange with Africans until the Late Pleistocene, when modern humans then dispersed into Eurasia in two waves. Advances in population genomics and methods applying evolutionary theory to the fossil record will serve to further clarify modern human origins and the out-of-Africa process.
    No preview · Article · Jan 2016 · Quaternary International
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    • "The major consensus regarding how and when anatomically modern humans On the other hand, craniofacial morphology observed among some of the most ancient remains in the Americas (Paleoamericans) has been described as much closer to African and Australo- Melanesians populations than to the modern series of Native Americans (Neves et al., 2003; Neves and Hubbe, 2005; Neves et al., 2007a; Hubbe et al., 2010). Thus, differences in craniofacial morphology pattern between early and late Americans have been considered abrupt and have been explained by assuming the existence of two separate migration events into the continent: the first representatives are the Paleoamericans, having a distinct morphology that might be a retention of the morphological pattern seen in the first modern humans leaving Africa, between 70 and 55 thousand years ago (Mellars, 2006), and that would thus precede the morphological differentiation of East Asian populations that likely occurred during the Pleistocene/Holocene boundary and which would have given rise to all modern Native Americans through a second (more recent) wave into the Americas (Hubbe et al., 2010). This view assume the existence of a suprapopulation unit of morphological affinity (classically named as Mongoloids) joining recent North Asians and late Holocene Native Americans (Neves et al., 2003), with a Middle/Late Holocene survival of Paleoamerican morphology reported for Sabana de Bogota, Colombia (Neves et al., 2007b) and Baja California, Mexico (Gonz alez-Jos e et al., 2003). "
    [Show abstract] [Hide abstract] ABSTRACT: During its expansion across the globe, Homo sapiens successfully survived to major adaptive challenges as a species, inviting scientific research to plunge into the particularities of continental settlement dynamics. A recurrent paleoanthropological concern is about the understanding of the great deal of craniofacial diversity that evolved into the Americas, which includes a vector of continuum variation between a generalized morphology observed among humans groups leading the Out-of-Africa dispersion, and a derived set of craniofacial traits classically labeled as "mongoloid" and that would have arise in Asia during the Holocene. Here, we use geometric morphometric techniques and multivariate statistics along with quantitative genetic approaches to look more closely into the human craniofacial evolutionary history during the Late Pleistocene-Early Holocene from Asia and the New World. We detected significant signals of deviation of the neutral evolutionary expectations, suggesting an important action of non-stochastic evolution (e.g. natural selection, phenotypic plasticity) in the Americas. We also found further support to the Recurrent Gene Flow model that refers to an ancestral, founder population experiencing a standstill in Beringia, and exhibiting high within-group craniofacial variation. This original, internally variable stock would have been the ancestral source of variation that fuelled the subsequent local micro evolution of other derived phenotypic patterns, giving origin to the craniofacial diversity observed among Holocene Native American samples.
    Full-text · Article · Nov 2015 · Quaternary International
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