Late Pleistocene/Holocene craniofacial morphology in Mesoamerican Paleoindians: Implications for the peopling of the New World

Global patterns of the cranial form of modern human populations described by analysis of a 3D surface homologous model

This study assessed the regional diversity of the human cranial form by using geometric homologous models based on scanned data from 148 ethnic groups worldwide. This method adopted a template-fitting technique for a nonrigid transformation via the iterative closest point algorithm to generate the homologous meshes. Through the application of principal component analysis to 342 sampled homologous models, the largest variation was detected in overall size, and small South Asian crania were clearly verified. The next greatest diversity was found in the length/breadth proportion of the neurocranium, which showed the contrast between the elongated crania of Africans and the globular crania of Northeast Asians. Notably, this component was slightly correlated with the facial profile. Well-known facial features, such as the forward projection of the cheek among Northeast Asians and compaction of the European maxilla, were reconfirmed. These facial variations were highly correlated with the calvarial outline, particularly the degree of frontal and occipital inclines. An allometric pattern was detected in facial proportions in relation to overall cranial size; in larger crania, the facial profiles tend to be longer and narrower, as demonstrated among many American natives and Northeast Asians. Although our study did not include data on environmental variables that are likely to affect cranial morphology, such as climate or dietary conditions, the large datasets of homologous cranial models will be usefully available for seeking various attributions to phenotypic skeletal characteristics.

A genomic perspective on South American human history

It has generally been accepted that the current indigenous peoples of the Americas are derived from ancestors from northeastern Asia. The latter were believed to have spread into the American continent by the end of the Last Glacial Maximum. In this sense, a joint and in-depth study of the earliest settlement of East Asia and the Americas is required to elucidate these events accurately. The first Americans underwent an adaptation process to the Americas' vast environmental diversity, mediated by biological and cultural evolution and niche construction, resulting in enormous cultural diversity, a wealth of domesticated species, and extensive landscape modifications. Afterward, in the Late Holocene, the advent of intensive agricultural food production systems, sedentism, and climate change significantly reshaped genetic and cultural diversity across the continent, particularly in the Andes and Amazonia. Furthermore, starting around the end of the 15th century, European colonization resulted in massive extermination of indigenous peoples and extensive admixture. Thus, the present review aims to create a comprehensive picture of the main events involved in the formation of contemporary South American indigenous populations and the dynamics responsible for shaping their genetic diversity by integrating current genetic data with evidence from archeology, linguistics and other disciplines.

Digital restoration of the Wilson-Leonard 2 Paleoindian skull (~10,000 BP) from central Texas with comparison to other early American and modern crania

OBJECTIVES

Craniofacial morphology (CFM) is often used to address questions about the biological affinities of the earliest Americans, or Paleoindians, but resolution is complicated in part by a lack of well-preserved crania. The Wilson-Leonard 2 (WL-2) Paleoindian skull from Texas has never been fully analyzed because it is crushed and cannot be physically reconstructed. This study employs a digital restoration for comprehensive assessment and analysis of WL-2.

MATERIALS AND METHODS

High-resolution CT data and geometric morphometrics are used to restore the WL-2 skull and analyze its morphology using 65 craniometric measurements acquired on the restoration. These data allow for a full morphological description and multivariate (Mahalanobis Distance and Principal Component) comparisons to other Paleoindians and recent populations.

RESULTS

WL-2 has a long, narrow braincase, and a short, modestly prognathic face. Compared with other Paleoindians, she is individually similar to several skulls from Brazil, but aligns most closely with pooled samples from the US and Mexico. WL-2 is most similar to recent populations from Europe, Asia, and the Americas, and markedly different to those from Africa and Australia.

DISCUSSION

The overall morphology of WL-2 and her association with Asians and Europeans align well with trends identified in other CFM analyses. Her affinity to recent Amerindians contrasts with the findings of many previous CFM studies, but is seemingly consistent with molecular analyses suggesting a close relationship between some Paleoindians and modern American Indians. This study demonstrates the potential for using digital anthropological methods to study other Paleoindian crania whose data value is limited by physical destruction and/or deformation.

Population level comparisons in central Mexico using cranial nonmetric traits

OBJECTIVES

We study the genetic diversity between Classic Teotihuacan and its neighboring towns trying to understand how far or close they are at the genetic level.

MATERIALS AND METHODS

We use cranial nonmetric traits to study a sample of 280 adult skulls from archaeological sites running from the late Preclassic to the early Postclassic. Samples of Classic Teotihuacan were studied for La Ventilla and San Sebastián Xolalpan neighbors. For the Epiclassic period, samples from Xaltocan, Toluca valley, Mogotes and Xico were used. For the Preclassic and Postclassic samples from Xico were also used. We used a parametric bootstrap for the mean measure of divergence for the statistical analysis.

RESULTS

Samples from Xico have small biodistance from Preclassic to Postclassic. Samples from Los Mogotes differ depending on the functional context of deposition, with individuals from household burials (funerary) differing from non-funerary, ceremonial interments and exhibiting affinities to Epiclassic samples from Toluca valley. Epiclassic populations from Xaltocan vary significantly from any samples analyzed. Samples from Classic period Teotihuacan vary considerably among them but form a separate genetic group from all the other populations under study.

CONCLUSIONS

The great biodistance separation among Classic Teotihuacan and its neighbor villages of central Mexico let us conclude that, contrary from the classical idea that those villages were confirmed by the inhabitants of Teotihuacan's collapse: They indeed remain as separate populations by themselves.

New evidence for an early settlement of the Yucatán Peninsula, Mexico: The Chan Hol 3 woman and her meaning for the Peopling of the Americas

Human presence on the Yucatán Peninsula reaches back to the Late Pleistocene. Osteological evidence comes from submerged caves and sinkholes (cenotes) near Tulum in the Mexican state of Quintana Roo. Here we report on a new skeleton discovered by us in the Chan Hol underwater cave, dating to a minimum age of 9.9±0.1 ky BP based on ²³⁰Th/U-dating of flowstone overlying and encrusting human phalanges. This is the third Paleoindian human skeleton with mesocephalic cranial characteristics documented by us in the cave, of which a male individual named Chan Hol 2 described recently is one of the oldest human skeletons found on the American continent. The new discovery emphasizes the importance of the Chan Hol cave and other systems in the Tulum area for understanding the early peopling of the Americas. The new individual, here named Chan Hol 3, is a woman of about 30 years of age with three cranial traumas. There is also evidence for a possible trepanomal bacterial disease that caused severe alteration of the posterior parietal and occipital bones of the cranium. This is the first time that the presence of such disease is reported in a Paleoindian skeleton in the Americas. All ten early skeletons found so far in the submerged caves from the Yucatán Peninsula have mesocephalic cranial morphology, different to the dolicocephalic morphology for Paleoindians from Central Mexico with equivalent dates. This supports the presence of two morphologically different Paleoindian populations for Mexico, coexisting in different geographical areas during the Late Pleistocene-Early Holocene.

Complex Nature of Hominin Dispersals: Ecogeographical and Climatic Evidence for Pre-Contact Craniofacial Variation

Coordinate data analysis of ancient crania from the New World reveals complexity in interpretation when addressing ancient population dispersals. The results of this study generally support a geographic patterning for the New World; however, it also revealed a much more complex and multifactorial mechanism shaping craniofacial morphology that should be considered when investigating ecogeographic models for hominin dispersals. We show that craniofacial variation is not the result of a single mechanism but is a much more complex interaction of environmental and microevolutionary forces.

Sex estimation from cranial morphological traits: Use of the methods across American Indians, modern North Americans, and ancient Egyptians

This paper focuses on estimating sex by visual assessment of human cranial morphology. Practitioners in the field report variation in sexual dimorphism across populations. This study evaluates again the general hypothesis that populations vary in their pattern of sexual dimorphism. Specifically, the study tests the degree of expression of four cranial morphological traits (glabella, supraorbital margins, nuchal crest, and mastoid process) across three samples from different time periods and which vary in sociocultural transitions: 1) modern Americans of rural and urban areas spanning the last 186 years; 2) Dynastic Egyptians; and 3) Averbuch American Indians, spanning approximately 1255 CE to 1425 CE, from the southeastern United States. These three populations were specifically chosen for sampling as they represent distinct temporal and groups of varied ancestral composition. Crania from these samples were scored 1-5, with 1 being consistent with expected female morphology. The estimated sex was compared to either documented sex (when available) or discriminant functions derived from craniometrics. Freeman-Fisher-Halton tests examined sample differences, within sexes, affecting the visual assessment method. Post hoc tests were applied to pinpoint where the differences lie between the samples. The findings of this study support the hypothesis that the method does not estimate the sex of crania from all populations in the same manner, indicating that populations display differing patterns of sexual dimorphism. However, understanding these patterns and adjusting for how the method is applied will lead to reliable assessments. A relative frequency table and graphs of distributions are provided for practitioners who can use the information to make successful assessments of sex.

Lagoa Santa's contribution to the origins and life of early Americans

The region of Lagoa Santa, Central-Eastern Brazil, provides an exceptional archeological record about Late Pleistocene/Early Holocene occupation of the Americas. Since the first interventions made by the Danish naturalist Peter Lund in the 19th century, hundreds of human skeletons have been exhumed in the region. These skeletons are complemented by a rich botanic, faunal, technological, and geomorphological archeological record. We explore here the contributions of Lagoa Santa material to the origins and lifestyle of early Americans, providing an historic background. Cranial morphology of Lagoa Santa skeletons allowed the proposition of a model of two biological components for the occupation of the Americas, in which early Americans are morphologically similar to people of African and Australo-Melanesian origin. Furthermore, the archeological record in the region has revealed an intense use of plant resources, a restricted spatial distribution, and the symbolic elaboration of local hunter-gatherers, unveiling a distinct lifestyle compared to early North American populations.

Fueguian crania and the circum-Pacific rim variation

OBJECTIVES

The Fueguians are descendants of the first settlers of America, a 'relict' isolated geographically for 10,000 years. We compared their cranial variation with other Americans, and samples from Asia and Australia to know whether the modern extinct Fueguians can be considered Paleoamericans or not.

MATERIALS AND METHODS

Herein we study 176 Fuego-Patagonian skulls, the largest cranial sample to be studied, refined and well documented, using CVA, and the D² of Mahalanobis. The affinities between populations and sexual dimorphism were jointly studied.

RESULTS

Terrestrial hunters (Selknam) have a different cranial morphology from sea canoeists (Yamana, Alakaluf) particularly with regard to cranial size and robustness. In the American context, there are extreme differences between the canoeists of Santa Cruz (California) and the Eskimos and canoeists of Fuego-Patagonia in terms of cranial size, prognathism and development of the frontal region. Fueguian canoeists are cranially closer to the Californian ones than to their Fueguian neighbors, the Selknam. Our results favor the hypothesis of two different flows for the origin of the first populators of Tierra del Fuego.

DISCUSSION

We concluded that the robusticity of some Fuegians (Selknam) might be the result of an allometric pattern of overall robusticity expression well as a result of epigenetics or differential reproduction (Larsen, 2015:264) or hypothetical endocrine changes (Bernal et al. in Am J Hum Biol 2006;18:748-765). When compared with three Australian-Melanesian series, the group comprising Amerindians, Ainu, and Eskimos clusters together as they are all extremely different from the former in terms of both cranial size and shape.

Genetic evidence for two founding populations of the Americas

Genetic studies have been consistent with a single common origin of Native American groups from Central and South America^1-4. However, some morphological studies have suggested a more complex picture, whereby the northeast Asian affinities of present-day Native Americans contrast with a distinctive morphology seen in some of the earliest American skeletons, which share traits with present-day Australasians (indigenous groups in Australia, Melanesia, and island southeast Asia)^5-8. Here we analyze genome-wide data to show that some Amazonian Native Americans descend partly from a Native American founding population that carried ancestry more closely related to indigenous Australians, New Guineans and Andaman Islanders than to any present-day Eurasians or Native Americans. This signature is not present to the same extent or at all in present-day Northern and Central Americans or a ~12,600 year old Clovis genome, suggesting a more diverse set of founding populations of the Americas than previously accepted.

POPULATION GENETICS. Genomic evidence for the Pleistocene and recent population history of Native Americans

How and when the Americas were populated remains contentious. Using ancient and modern genome-wide data, we found that the ancestors of all present-day Native Americans, including Athabascans and Amerindians, entered the Americas as a single migration wave from Siberia no earlier than 23 thousand years ago (ka) and after no more than an 8000-year isolation period in Beringia. After their arrival to the Americas, ancestral Native Americans diversified into two basal genetic branches around 13 ka, one that is now dispersed across North and South America and the other restricted to North America. Subsequent gene flow resulted in some Native Americans sharing ancestry with present-day East Asians (including Siberians) and, more distantly, Australo-Melanesians. Putative "Paleoamerican" relict populations, including the historical Mexican Pericúes and South American Fuego-Patagonians, are not directly related to modern Australo-Melanesians as suggested by the Paleoamerican Model.

The cranial morphology of the Botocudo Indians, Brazil

The Botocudo Indians were hunter-gatherer groups that occupied the East-Central regions of Brazil decimated during the colonial period in the country. During the 19th century, craniometric studies suggested that the Botocudo resembled more the Paleoamerican population of Lagoa Santa than typical Native Americans groups. These results suggest that the Botocudo Indians might represent a population that retained the biological characteristics of early groups of the continent, remaining largely isolated from groups that gave origin to the modern Native South American variation. Moreover, recently, some of the Botocudo remains have been shown to have mitochondrial and autosomal DNA lineages currently found in Polynesian populations. Here, we explore the morphological affinities of Botocudo skulls within a worldwide context. Distinct multivariate analyses based on 32 craniometric variables show that 1) the two individuals with Polynesian DNA sequences have morphological characteristics that fall within the Polynesian and Botocudo variation, making their assignation as Native American specimens problematic, and 2) there are high morphological affinities between Botocudo, Early Americans, and the Polynesian series of Easter Island, which support the early observations that the Botocudo can be seen as retaining the Paleoamerican morphology, particularly when the neurocranium is considered. Although these results do not elucidate the origin of the Polynesian DNA lineages among the Botocudo, they support the hypothesis that the Botocudo represent a case of late survival of ancient Paleoamerican populations, retaining the morphological characteristics of ancestral Late Pleistocene populations from Asia.

Late Pleistocene human skeleton and mtDNA link Paleoamericans and modern Native Americans

Because of differences in craniofacial morphology and dentition between the earliest American skeletons and modern Native Americans, separate origins have been postulated for them, despite genetic evidence to the contrary. We describe a near-complete human skeleton with an intact cranium and preserved DNA found with extinct fauna in a submerged cave on Mexico's Yucatan Peninsula. This skeleton dates to between 13,000 and 12,000 calendar years ago and has Paleoamerican craniofacial characteristics and a Beringian-derived mitochondrial DNA (mtDNA) haplogroup (D1). Thus, the differences between Paleoamericans and Native Americans probably resulted from in situ evolution rather than separate ancestry.

Towards a reconciling model about the initial peopling of America

The last two decades have seen numerous debates in the field of the initial settlement of America and noteworthy was the disagreement between physical and molecular anthropologists. Recently, it has been pointed out that this discordance could partly originate from the description methods and classification labels used in craniometry, which did not account fairly for the within-sample and within-group variance. From there, a federative model for the initial peopling of America has been designed which could now explain the biological variability found at both the craniofacial and genetic level. This is a major step in the study of the initial settlement of America, which deserved to be highlighted. The present paper recalls the two conflicting models that prevailed for the last 20 years of anthropological studies in America before browsing the newly accepted hypothesis about the origin of the first Amerindians as seen by its authors. Lastly, the article evokes some areas of investigations, which could furnish significant fallouts about the dynamics of the peopling of Americas in the future.

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

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.

A statistical evaluation of models for the initial settlement of the american continent emphasizes the importance of gene flow with Asia

Although there is agreement in that the Bering Strait was the entry point for the initial colonization of the American continent, there is considerable uncertainty regarding the timing and pattern of human migration from Asia to America. In order to perform a statistical assessment of the relative probability of alternative migration scenarios and to estimate key demographic parameters associated with them, we used an approximate Bayesian computation framework to analyze a data set of 401 autosomal microsatellite loci typed in 29 native American populations. A major finding is that a single, discrete, wave of colonization is highly inconsistent with observed levels of genetic diversity. A scenario with two discrete migration waves is also not supported by the data. The current genetic diversity of Amerindian populations is best explained by a third model involving recurrent gene flow between Asia and America, after initial colonization. We estimate that this colonization involved about 100 individuals and occurred some 13,000 years ago, in agreement with well-established archeological data.

Metric and nonmetric dental variation and the population structure of the Ainu

Gene flow and genetic drift are important factors affecting geographic variations in human phenotypic traits. In the present study, the effects of gene flow from an outside source on the pattern of within- and among-group variation of the Ainu from Sakhalin Island and three local groups of Hokkaido are examined by applying an R-matrix approach to metric and nonmetric dental data. The comparative samples consist of their ancestral and neighboring populations, such as the Neolithic Jomon, the subsequent Epi-Jomon/Satsumon, the Okhotsk culture people who migrated from Northeast Asia to the northeastern part of Hokkaido during a period 1600-900 years B.P., and modern non-Ainu Japanese. The results obtained by using the census population sizes of the regional groups of the Ainu as an estimate of relative effective population size suggest the possibility of an admixture between the Okhotsk culture people and the indigenous inhabitants in Hokkaido, at least in the coastal region along the Sea of Okhotsk. Such gene flow from Northeast Asian continent may have exerted an effect on the genetic structure of the contemporary Ainu. The present findings indicate that the population structure, as represented by genetic drift and gene flow, tend to be obscured in the results obtained by standard statistical methods such as Mahalanobis' generalized distance and Smith's MMDs. The present extension of the R-matrix approach to metric and nonmetric dental data provide results that can be interpreted in terms of a genetically, archaeologically, and prehistorically suggested pattern of gene flow and isolation.

The peopling of America: craniofacial shape variation on a continental scale and its interpretation from an interdisciplinary view

Twenty-two years ago, Greenberg, Turner and Zegura (Curr. Anthropol. 27,477-495, 1986) suggested a multidisciplinary model for the human settlement of the New World. Since their synthesis, several studies based mainly on partial evidence such as skull morphology and molecular genetics have presented competing, apparently mutually exclusive, settlement hypotheses. These contradictory views are represented by the genetic-based Single Wave or Out of Beringia models and the cranial morphology-based Two Components/Stocks model. Here, we present a geometric morphometric analysis of 576 late Pleistocene/early Holocene and modern skulls suggesting that the classical Paleoamerican and Mongoloid craniofacial patterns should be viewed as extremes of a continuous morphological variation. Our results also suggest that recent contact among Asian and American circumarctic populations took place during the Holocene. These results along with data from other fields are synthesized in a model for the settlement of the New World that considers, in an integrative and parsimonious way, evidence coming from genetics and physical anthropology. This model takes into account a founder population occupying Beringia during the last glaciation characterized by high craniofacial diversity, founder mtDNA and Y-chromosome lineages and some private autosomal alleles. After a Beringian population expansion, which could have occurred concomitant with their entry into America, more recent circumarctic gene flow would have enabled the dispersion of northeast Asian-derived characters and some particular genetic lineages from East Asia to America and vice versa.

The late Pleistocene dispersal of modern humans in the Americas

When did humans colonize the Americas? From where did they come and what routes did they take? These questions have gripped scientists for decades, but until recently answers have proven difficult to find. Current genetic evidence implies dispersal from a single Siberian population toward the Bering Land Bridge no earlier than about 30,000 years ago (and possibly after 22,000 years ago), then migration from Beringia to the Americas sometime after 16,500 years ago. The archaeological records of Siberia and Beringia generally support these findings, as do archaeological sites in North and South America dating to as early as 15,000 years ago. If this is the time of colonization, geological data from western Canada suggest that humans dispersed along the recently deglaciated Pacific coastline.

“Zuzu” strikes again—Morphological affinities of the early holocene human skeleton from Toca dos Coqueiros, Piaui, Brazil

The Serra da Capivara National Park in northeastern Brazil is one of the richest archaeological regions in South America. Nonetheless, so far only two paleoindian skeletons have been exhumed from the local rockshelters. The oldest one (9870 +/- 50 BP; CAL 11060 +/- 50), uncovered in Toca dos Coqueiros and known as "Zuzu," represents a rare opportunity to explore the biological relationships of paleoindian groups living in northeastern Brazil. As previously demonstrated, South and Central America Paleoindians present skull morphology distinct from the one found nowadays in Amerindians and similar to Australo-Melanesians. Here we test the hypothesis that Zuzu shows higher morphological affinity with Paleoindians. However, Zuzu is a controversial skeleton since previous osteological assessments have disagreed on several aspects, especially regarding its sex. Thus, we compared Zuzu to males and females independently. Morphological affinities were assessed through clustering of principal components considering 18 worldwide populations and through principal components analysis of the individual dispersion of five key regions for America's settlement. The results obtained do not allow us to refute the hypothesis, expanding the known geographical dispersion of the Paleoindian morphology into northeast Brazil. To contribute to the discussion regarding Zuzu's sex, a new estimation is presented based on visual inspection of cranial and post-cranial markers, complemented by a discriminant analysis of its morphology in relation to the paleoindian sample. The results favor a male classification and are consistent with the mortuary offerings found in the burial, yet do not agree with a molecular determination.

Human skeletal remains from Sabana de Bogotá, Colombia: A case of Paleoamerican morphology late survival in South America?

Human skeletal remains of the first Americans are scarce, especially in North America. In South America the situation is less dramatic. Two important archaeological regions have generated important collections that allow the analysis of the cranial morphological variation of the Early Americans: Lagoa Santa, Brazil, and Sabana de Bogotá, Colombia. Human crania from the former region have been studied by one of us (WAN) and collaborators, showing that the cranial morphology of the first South Americans was very different from that prevailing today in East Asia and among Native Americans. These results have allowed for proposing that the New World may have been colonized by two different biological populations in the final Pleistocene/early Holocene. In this study, 74 human skulls dated between 11.0 and 3.0 kyr, recovered in seven different sites of Sabana de Bogotá, Colombia, were compared with the world cranial variation by different multivariate techniques: Principal Components Analysis, Multidimensional Scaling, and Cluster of Mahalanobis distance matrices. The Colombian skeletal remains were divided in two chronological subgroups: Paleocolombians (11.0-6.0 kyr) and Archaic Colombians (5.0-3.0 kyr). Both quantitative techniques generated convergent results: the Paleocolombians show remarkable similarities with Lagoa Santa and with modern Australo-Melanesians. Archaic Colombians exhibited the same morphological patterns and associations. These findings support our long-held proposition that the early American settlement may have involved two very distinct biological populations coming from Asia. On the other hand, they suggest the possibility of late survivals of the Paleoamerican pattern not restricted to isolated or marginal areas, as previously thought.

Early Holocene human skeletal remains from Sumidouro Cave, Lagoa Santa, Brazil: History of discoveries, geological and chronological context, and comparative cranial morphology

In this work, we present new evidence supporting the idea that the first Americans were very distinct from late and recent Native Americans and Asians in terms of cranial morphology. The study is based on 30 early Holocene specimens recovered from Sumidouro Cave (Lagoa Santa region, central Brazil) by Peter Lund in 1843. Sumidouro is the largest known collection of Paleoindian skulls deriving from a single site. Six different multivariate statistical methods were applied to assess the morphological affinities of the Sumidouro skulls in comparison to Howells' worldwide extant series and late archaic Brazilian series (Base Aérea and Tapera). The results show a clear association between Sumidouro and Australo-Melanesians and none with late Asian and Amerindian series. These results are in accordance with those of previous studies of final Pleistocene/early Holocene human skulls from South, Central, and North America, attesting to a colonization of the New World by at least two different, succeeding biological populations: an early one with a cranial morphology similar to that found today in the African and Australian continents, and a later one with a morphology similar to that found today among northeastern Asians.

East–West cranial differentiation in pre-Columbian human populations of South America

South Amerindians are frequently thought of as a rather biologically homogeneous megapopulation. However, when native South Americans are assessed by information coming from DNA variability analysis, they resolve into two, major distinct entities of Eastern and Western zones. The purpose of this study is to investigate if the same dual pattern emerges from craniometric data. We approached this question by means of functional craniometric variables. We found strong evidence that Westerners and Easterners constitute two distinct and independent microevolutionary universes when cranial morphology is assessed. The existence of a third universe, Northwest, cannot be completely ruled out, but needs further investigation. We also discovered that Westerners and Easterners present similar degrees of internal variation, contrary to the findings of geneticists and molecular biologists. Palaeoamericans seem to be more similar to Easterners than to Westerners and North-Westerners. Our results suggest that this East-West cranial differentiation is more probably the result of differential rates of genetic drift and gene flow acting on each side of the Cordillera. However, different intensities of gene flow between Palaeoamericans and Amerindians in the highlands and in the lowlands cannot be completely dismissed as a possible explanation for the differentiation found.