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Recent discoveries constrain the presence of hominins in North Africa since ca. 2.4 Ma and in China since ca. 2.1 Ma, providing a new temporal framework for the earliest migration out of Africa. No Paleolithic sites of such age exist in the Levant, the natural corridor between Africa and Asia. The Dawqara Formation in the Zarqa Valley, Jordan, has been known since the early 1980s because of the presence of artifacts at different stratigraphic levels within its fluvial sediments, consisting of choppers, cores, and flakes. Although most of the artifacts display signs of transport, they bear unambiguous evidence of manufacture, and document hominin presence in the Zarqa Valley during the deposition of Dawqara Formation. Based on integrated chronology provided by paleomagnetic, 40Ar/39Ar, and U-Pb dating methods, our study shows that the Dawqara Formation was deposited between 2.52 ± 0.01 Ma and the Matuyama–Olduvai geomagnetic reversal (1.95 Ma). By linear interpolation, the artifact-bearing stratigraphic levels within the Dawqara Formation have ages of ca. 2.48 Ma, 2.24 Ma, 2.16 Ma, 2.06 Ma, and 1.95 Ma, respectively, possibly documenting continuous hominin presence in the Zarqa Valley. These new ages for the Dawqara assemblage constrain the earliest hominin dispersal out of Africa to the beginning of the Pleistocene, and pre-date by ca. 300 kyr the hominin occupation of Chinese Loess Plateau. • The Levant is a key area to investigate the exit of hominins out of Africa. • The Zarqa Valley, Jordan, yielded Oldowan tools and mammal fossils from Dawqara Fm. • New chronologic constraints were derived from surveys and dating methods. • Constrained to 2.5–2.0 Ma, the Dawqara tools document the earliest hominin presence out of Africa. [ABSTRACT FROM AUTHOR]

Abstract: The majority of extinct Brazilian late Quaternary mammal (i.e. megafauna) remains comes from cave deposits and was retrieved through excavations lacking detailed stratigraphical context. This poses a major problem since these deposits present multifaceted processes of formation. Based on the meticulous excavation of a pitfall site within Cuvieri Cave, Minas Gerais, eastern Brazil, this article describes a critical, albeit subtle, temporal discontinuity between different fossiliferous sedimentary facies and discusses its significance to the contextualization of the paleontological remains recovered from the site. The discontinuity was described based on sedimentary analyses, bone deposition processes, taxonomy and AMS radiocarbon chronology. Two facies were distinguished and named according to their color and texture: an upper dark brown silt-loam (BSL) and a lower dark reddish brown silt-loam (RBSL). Besides color differences, they present differences in grain size distribution and chemical composition. These analyses show that the RBSL has in its composition only half the sand and one third more the silt than BSL. It also shows that mean percent values for the RBSL in comparison to the BSL are higher for silica (42.35 versus 15.80), aluminum (18.63 versus 7.58) and iron (8.45 versus 3.79) and lower for calcium (10.07 versus 36.14) and volatiles (13.86 versus 30.10). These differences are attributed to changes in sediment source and entrance route. Differences were also observed in the faunal remain analyses. RBSL has abundant megafauna remains originally deposited within this facies, while the scarce megafauna material found in BSL is the result of mixing processes. Despite these differences, animal entrapment is considered the best scenario to explain bone accumulation in both facies. AMS radiocarbon dates indicate that the BSL was deposited during the Holocene, with dates ranging from 8580calyr BP to the present, while the RBSL deposition dates to the Holocene/Pleistocene transition (13,600–10,660calyr BP). Radiocarbon dating also indicates that the subtle erosional surface that limits both facies represents a temporal gap between a minimum age of 8.4calkyr BP and a maximum age of 11.0calkyr BP. The recognition of this discontinuity allows for a more accurate interpretation of bone accumulation, enabling the differentiation of faunal assemblages that might otherwise be considered part of a continuum. [Copyright &y& Elsevier]

Abstract: The geochronology and taphonomy of internationally important fossil bearing cave deposits were studied, both in the semi-arid Northern Bahia area and the subtropical southeastern Lagoa Santa area of Brazil. Taphonomic analysis suggests that the processes responsible for bone accumulation in the Brazilian caves vary between sites, and taphonomic bias can therefore be significant in causing differences in faunal composition. In the Toca da Boa Vista caves the presence of single articulated skeletons, and the entrance-related distribution indicate that random penetration of animals is the main mechanism of fossil accumulation, a process that biases the assemblage to smaller species, and takes place over extended time periods. In nearby Toca dos Ossos cave transport by runoff in the cave river is predominant, and biases the fauna remains to larger more robust bones and species. Deposition probably also occurred only at times of enhanced runoff giving a more contemporaneous assemblage. Similar processes were responsible for emplacement of the copious fossil remains in the more humid Lagoa Santa area, where terrigenous fossil deposits are found intercalated by massive speleothem calcite layers. In this area runoff under a drier climate probably accounts for the sediment emplacement inside caves. In both areas the mode of emplacement implies bias in the fossil record, resulting in fossil assemblages that do not mirror surface faunas, limiting palaeoenvironmental reconstruction. Mass spectrometric U-series analysis of speleothem calcite overlaying fossil remains gives minimum ages for fossil deposition. These ages confirm the previous view that many of the deposits derive from the late glacial, but also show that much older material (some >350,000 yr) is also present. The habitat requirements of critical fossil species such as bats and monkeys strongly suggest that they derive from much wetter periods when forest cover was present in the currently semi-arid Northern Bahia area. Taphonomy exerts a major control on the diversity and mode of emplacement of cave fossil deposits in eastern Brazil and thus detailed sedimentological and hydrological studies coupled with a sound geochronological approach are essential in quantifying the relative importance of each taphonomic processes before faunal and palaeoecological interpretations can be attempted. [Copyright &y& Elsevier]

Here we present a Geometric Morphometric study of five skulls from the Early Holocene from Mexico basin. They are: Peñón iii, Metro Balderas, Chimalhuacán and Cueva del Tecolote specimens. Results show that those crania are morphologically more associated to the Paleoamericans from Brazil and other late Pleistocene remains from Asia and Africa, than to several Mexican and Amerindian modern series. The large geographic dispersal of Paleoamericans and their presence in Mexico during the Early Holocene raises new issues about the continent's settlement scenario. [ABSTRACT FROM AUTHOR]

Karst caves are suitable environments for the accumulation and preservation of fossils. Cave deposits are often complex and the environmental conditions within cave sites result from intricate interactions between various biological, physical and chemical factors. However, it is not fully understood how the complexity of the environmental conditions of caves influences bone diagenesis. The study of the initial stages of bone diagenesis depends to a large extent on understanding the changes in the bone histology. To contribute to this issue, we examine a set of postmortem changes affecting the bone histology of Quaternary mammals that accumulated naturally in Locus 2, a pitfall site in Cuvieri Cave, located in the tropical region of Brazil. Our analyses show that bones deposited in caves may be subject to a peculiar set of environmental conditions that in tropical regions may prevent the preservation of bone histological structure. The effect of diagenetic processes on the bones differs depending on the taphonomic stage of the bone and the diagenetic alterations appear to have influenced each other. The deposition of bioclasts following the entrapment of individuals in Locus 2 favours the proliferation of bacteria on bones and appears to be important in directing the diagenetic alteration. The hydrological regime of the cave, that is recharge with potential phases of higher humidity, also is important in directing the diagenetic alteration and further decreased the preservation potential of the bone microstructure. The formation of macroscopic and microscopic cracks related to bone weathering in caves shows that the taphonomic processes peculiar to these environments are poorly understood, highlighting the need for more research to be conducted on cave taphonomy. • Cave deposits are often very complex. • Environmental conditions inside caves are dictated by several factors. • The influence of this complexity on bone diagenesis is poorly understood. • The histology of bones from Cuvieri Cave were altered by diagenetic processes. • Environmental conditions on tropical caves may be very destructive to bone histology. [ABSTRACT FROM AUTHOR]

SARS-CoV-2 caused the pandemic situation experienced since the beginning of 2020, and many countries faced the rapid spread and severe form of the disease. Mechanisms of interaction between the virus and the host were observed during acute phase, but few data are available when related to immunity dynamics in convalescents. We conducted a longitudinal study, with 51 healthy donors and 62 COVID-19 convalescent patients, which these had a 2-month follow-up after symptoms recovery. Venous blood sample was obtained from all participants to measure blood count, subpopulations of monocytes, lymphocytes, natural killer cells and dendritic cells. Serum was used to measure cytokines, chemokines, growth factors, anti-N IgG and anti-S IgG/IgM antibodies. Statistic was performed by Kruskal-Wallis test, and linear regression with days post symptoms and antibody titers. All analysis had confidence interval of 95%. Less than 35% of convalescents were anti-S IgM+, while more than 80% were IgG+ in D30. Anti-N IgG decreased along time, with loss of seroreactivity of 13%. Eosinophil count played a distinct role on both antibodies during all study, and the convalescence was orchestrated by higher neutrophil-to-lymphocyte ratio and IL-15, but initial stages were marked by increase in myeloid DCs, B1 lymphocytes, inflammatory and patrolling monocytes, G-CSF and IL-2. Later convalescence seemed to change to cytotoxicity mediated by T lymphocytes, plasmacytoid DCs, VEGF, IL-9 and CXCL10. Anti-S IgG antibodies showed the longest perseverance and may be a better option for diagnosis. The inflammatory pattern is yet present on initial stage of convalescence, but quickly shifts to a reparative dynamic. Meanwhile eosinophils seem to play a role on anti-N levels in convalescence, although may not be the major causative agent. We must highlight the importance of immunological markers on acute clinical outcomes, but their comprehension to potentialize adaptive system must be explored to improve immunizations and further preventive policies., (© 2024. The Author(s).)

Sahelanthropus tchadensis has raised much debate since its initial discovery in Chad in 2001, given its controversial classification as the earliest representative of the hominin lineage. This debate extends beyond the phylogenetic position of the species, and includes several aspects of its habitual behavior, especially in what regards its locomotion. The combination of ancestral and derived traits observed in the fossils associated with the species has been used to defend different hypotheses related to its relationship to hominins. Here, the cranial morphology of Sahelanthropus tchadensis was assessed through 16 linear craniometric measurements, and compared to great apes and hominins through Principal Component Analysis based on size and shape and shape information alone. The results show that S. tchadensis share stronger morphological affinities with hominins than with apes for both the analysis that include size information and the one that evaluates shape alone. Since TM 266-01-060-1 shows a strong morphological affinity with the remaining hominins represented in the analysis, our results support the initial interpretations that S. tchadensis represents an early specimen of our lineage or a stem basal lineage more closely related to hominins than to Panini.

The origins of the genus Homo have been a focus of much debate in the paleoanthropological literature due to its importance in understanding the evolutionary trajectories that led to the appearance of archaic humans and our species. On the level of taxonomic classification, the controversies surrounding the origins of Homo are the result of lack of clear classification criteria that separate our genus from australopiths, given the general similarities observed between fossils ascribed to late australopiths and early Homo. The challenge in finding clear autapomorphies for Homo has even led to debates about the classification of Homo habilis and Homo rudolfensis as part of our genus. These debates are further complicated by the scarcity of fossils in the timeframe of appearance of our genus, making any fossils dated to between 3.0 and 2.5 Ma of particular relevance in the context of this discussion. The Ledi-Geraru mandible is one such fossils, which has called the attention of researchers due to its combination of primitive traits seen in Australopithecus and derived traits observed in later Homo. Despite being fragmented and poorly preserved, it is one of the key fossil specimens available from the period mentioned above.

Microsphere-based flow cytometry is a highly sensitive emerging technology for specific detection and clinical analysis of antigens, antibodies, and nucleic acids of interest. In this review, studies that focused on the application of flow cytometry as a viable alternative for the investigation of infectious diseases were analyzed. Many of the studies involve research aimed at epidemiological surveillance, vaccine candidates and early diagnosis, non-infectious diseases, specifically cancer, and emphasize the simultaneous detection of biomarkers for early diagnosis, with accurate results in a non-invasive approach. The possibility of carrying out multiplexed assays affords this technique high versatility and performance, which is evidenced in a series of clinical studies that have verified the ability to detect several molecules in low concentrations and with minimal sample volume. As such, we demonstrate that microsphere-based flow cytometry presents itself as a promising technique that can be adopted as a fundamental element in the development of new diagnostic methods for a number of diseases.

Recent discoveries of stone tools from Jordan (2.5 Ma) and China (2.1 Ma) document hominin presence in Asia at the beginning of the Pleistocene, well before the conventional Dmanisi datum at 1.8 Ma. Although no fossil hominins documenting this earliest Out of Africa phase have been found, on chronological grounds a pre-Homo erectus hominin must be considered the most likely maker of those artifacts. If so, this sheds new light on at least two disputed subjects in paleoanthropology, namely the remarkable variation among the five Dmanisi skulls, and the ancestry of Homo floresiensis., (© 2020 Wiley Periodicals LLC.)

The aim of this paper is to analyze the morphology of a skull from Candonga Cave (central Argentina), dating to the Pleistocene-Holocene transition, and to discuss its implications for the early peopling of South-America by Palaeoamerican and Amerindian populations. Although this cranium is fragmented, impeding the standard morphometric analysis, an alternative methodology ad hoc was implemented in order to obtain relevant information about the South American people origins. Results of measurements provide new information to reinforce the hypothesis that Paleoamerican crania possess similar morphological traits to those of current Fueguian populations, as previous studies have claimed, and to suggest that the cranium of Candonga has strong morphological affinities with Early Holocene specimens from Lagoa Santa (Brazil) and Late Holocene of Beagle Channel (Argentina), both belonging to Paleoamerican morphology.

The therapeutic strategies used in the treatment of hepatitis C are essentially based on the combination of direct-acting antiviral agents (DAAs). This therapy has been shown to be very effective in relation to patient adherence to treatment and has shown high rates of sustained virological response (SVR). However, the immunological dynamics of patients infected with HCV is poorly understood. This fact led us to investigate the immune system of naive and experienced patients, who we followed before the therapy and three months after the end of treatment. In this study, 35 naive and experienced Brazilian patients with chronic hepatitis C and 50 healthy donors (HD group) were studied. The analysis of the soluble immunological biomarkers was performed using the flow cytometry methodology. The SVR rate was >90% among the 35 patients. Before treatment, correlations in the naive HCV group demonstrated a mix of inflammatory response occurring with moderate correlations between chemokines, inflammatory cytokines, and Th2 profile, with a strong regulation between IL-10 and IL-17A. On the other hand, experienced patients demonstrated a poor interaction between cytokines, chemokines, and cells with a strong correlation between IL-10, IL-6, CXCL-10, and CD8 + besides the interactions between IFN- γ and IL-4. Furthermore, naive and experienced patients seem to have a distinct soluble biomarker profile; therefore, a long-term follow-up is needed to evaluate patients treated with DAAs., Competing Interests: The authors declare that there is no conflict of interests regarding the publication of this paper., (Copyright © 2019 Grenda Leite Pereira et al.)

This ethnography is about a particular human-animal relationship based on primatological research on groups of wild robust capuchin monkeys living in Parque Estadual Carlos Botelho (Brazil), one of the largest preserved areas of Atlantic Tropical Forest in the world. It emphasizes the complex situations that highlight the difficulty of making this research. This space integrates administrative, scientific and local interests, producing a unique cartography. We reflect on the scientific research considering the relations among primatologist, field assistant and other animals and comparing it with the hunt. "Hunt" is a model inspired in techniques and in some aspects of recreational hunt to expand the comprehension of a complex routine defined to obtain behavior data.

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., (© 2018 Wiley Periodicals, Inc.)

Evolutionary novelties in the skeleton are usually expressed as changes in the timing of growth of features intrinsically integrated at different hierarchical levels of development. As a consequence, most of the shape-traits observed across species do vary quantitatively rather than qualitatively, in a multivariate space and in a modularized way. Because most phylogenetic analyses normally use discrete, hypothetically independent characters, previous attempts have disregarded the phylogenetic signals potentially enclosed in the shape of morphological structures. When analysing low taxonomic levels, where most variation is quantitative in nature, solving basic requirements like the choice of characters and the capacity of using continuous, integrated traits is of crucial importance in recovering wider phylogenetic information. This is particularly relevant when analysing extinct lineages, where available data are limited to fossilized structures. Here we show that when continuous, multivariant and modularized characters are treated as such, cladistic analysis successfully solves relationships among main Homo taxa. Our attempt is based on a combination of cladistics, evolutionary-development-derived selection of characters, and geometric morphometrics methods. In contrast with previous cladistic analyses of hominid phylogeny, our method accounts for the quantitative nature of the traits, and respects their morphological integration patterns. Because complex phenotypes are observable across different taxonomic groups and are potentially informative about phylogenetic relationships, future analyses should point strongly to the incorporation of these types of trait.

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., ((c) 2007 Wiley-Liss, Inc.)

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., ((c) 2007 Wiley-Liss, Inc.)

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.

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.

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 South-American Paleoindians and extant Australo-Melanesians groups, supporting the hypothesis that two distinct biological populations could have colonized the New World in the Pleistocene/Holocene transition.

Increasing skeletal evidence from the U.S.A., Mexico, Colombia, and Brazil strongly suggests that the first settlers in the Americas had a cranial morphology distinct from that displayed by most late and modern Native Americans. The Paleoamerican morphological pattern is more generalized and can be seen today among Africans, Australians, and Melanesians. Here, we present the results of a comparative morphological assessment of a late Paleoindian/early archaic specimen from Capelinha Burial II, southern Brazil. The Capelinha skull was compared with samples of four Paleoindian groups from South and Central America and worldwide modern groups from W.W. Howells' studies. In both analyses performed (classical morphometrics and geometric morphometrics), the results show a clear association between Capelinha Burial II and the Paleoindians, as well as Australians, Melanesians, and Africans, confirming its Paleoamerican status.

In this study we compare the cranial morphology of several late Paleoindian skeletons uncovered at Santana do Riacho, Central Brazil, with worldwide human cranial variation. Mahalanobis Distance and Principal Component Analysis are used to explore the extra-continental morphological affinities of the Brazilian Paleoindian sample. Santana do Riacho is a late Paleoindian burial site where approximately 40 individuals were recovered in varying states of preservation. The site is located at Lagoa Santa/Serra do Cipó, State of Minas Gerais. The first human activities in this rockshelter date back to the terminal Pleistocene, but the burials are bracketed between circa 8200 and 9500BP. The collection contains only six skulls well-enough preserved to be measured. The Santana do Riacho late Paleoindians present a cranial morphology characterized by long and narrow neurocrania, low and narrow faces, with low nasal apertures and orbits. The multivariate analyses show that they exhibit strong morphological affinities with present day Australians and Africans, showing no resemblance to recent Northern Asians and Native Americans. These findings confirm our long held opinion that the settlement of the Americas was more complicated in terms of biological input than has been widely assumed. The working hypothesis is that two very distinct populations entered the New World by the end of the Pleistocene, and that the transition between the cranial morphology of the Paleoindians and the morphology of later Native Americans, which occurred around 8-9ka, was abrupt. This, in our opinion, is a more parsimonious explanation for the diversity detected than a long, local microevolutionary process mediated by selection and drift. The similarities of the first South Americans with sub-Saharan Africans may result from the fact that the non-Mongoloid Southeast Asian ancestral population came, ultimately, from Africa, with no major modification in the original cranial bau plan of the first modern humans.