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We propose an Ideal Specialization Model to help explain the diversity of population growth trajectories exhibited across archaeological regions over thousands of years. The model provides a general set of expectations useful for guiding empirical research, and we provide a concrete example by conducting a preliminary evaluation of three expectations in Central West Argentina. We use kernel density estimates of archaeological radiocarbon, estimates of paleoclimate, and human bone stable isotopes from archaeological remains to evaluate three expectations drawn from the model's dynamics. Based on our results, we suggest that innovations in the production of food and social organization drove demographic transitions and population expansion in the region. The consistency of population expansion in the region positively associates with changes in diet and, potentially, innovations in settlement and social integration.

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The southern Mendoza province, located in the northern region of Patagonia, was inhabited by hunter-gatherer groups until historic times. Previous archaeological studies have reported canid remains among faunal assemblages, which were assumed to be part of the human diet. However, the taxonomic identification and significance of these canids within human groups have raised questions. In this study, we used ancient DNA analysis, morphological examination and stable isotope analysis (δ13Ccol and δ15N) to re-evaluate the taxonomic assignment of a canid discovered at the Late Holocene burial site of Cañada Seca. Previous morphological identifications suggested that it belonged to the genus Lycalopex, but our results conclusively demonstrate that the individual belongs to the extinct fox species Dusicyon avus. This finding expands Dusicyon avus' known geographical distribution to Patagonia's northern extremity. Furthermore, statistical predictions based on genetic divergence undermine the hypothesis that hybridization between Canis and Dusicyon, facilitated by the introduction of domestic dogs, played a role in the extinction of Dusicyon species. On the other hand, our findings indicate that a Dusicyon avus individual shared a similar diet and was probably buried alongside humans, suggesting a close relationship between the two species during their lives and deaths.

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Researchers have long debated the degree to which Native American land use altered landscapes in the Americas prior to European colonization. Human-environment interactions in southern South America are inferred from new pollen and charcoal data from Laguna El Sosneado and their comparison with high-resolution paleoenvironmental records and archaeological/ethnohistorical information at other sites along the eastern Andes of southern Argentina and Chile (34-52°S). The records indicate that humans, by altering ignition frequency and the availability of fuels, variously muted or amplified the effects of climate on fire regimes. For example, fire activity at the northern and southern sites was low at times when the climate and vegetation were suitable for burning but lacked an ignition source. Conversely, abundant fires set by humans and infrequent lightning ignitions occurred during periods when warm, dry climate conditions coincided with ample vegetation (i.e., fuel) at midlatitude sites. Prior to European arrival, changes in Native American demography and land use influenced vegetation and fire regimes locally, but human influences were not widely evident until the 16th century, with the introduction of nonnative species (e.g., horses), and then in the late 19th century, as Euro-Americans targeted specific resources to support local and national economies. The complex interactions between past climate variability, human activities, and ecosystem dynamics at the local scale are overlooked by approaches that infer levels of land use simply from population size or that rely on regionally composited data to detect drivers of past environmental change.

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This study tests the hypothesis that the incorporation of cultigens about ca. 2000 years BP substantially changed hunter-gatherer subsistence and mobility in the Atuel River valley (Central-Western Argentina), where the frontier of pre-Hispanic domesticated resource dispersion was defined. Degenerative joint disease and entheseal change markers were analyzed on skeletal remains from Cañada Seca-1, a burial archaeological site with commingled skeletal remains dated about ca. 1500 years BP (MNI = 24). The results show lower mobility in comparison with hunter-gatherer remains from the neighboring Pampa region and quite different manual activities compared to low-level producers. These trends are explained as a result of a mixed subsistence strategy and mobility in an area where the incorporation of domesticated plants was neither a linear nor a fast process, and a stereotypical view proves to be insufficient to understand it. Although further information is required for future discussions, the present research highlights the potential of commingled skeletal remains for this kind of study.

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All crops are the product of a domestication process that started less than 12,000 years ago from one or more wild populations1,2. Farmers selected desirable phenotypic traits (such as improved energy accumulation, palatability of seeds and reduced natural shattering3) while leading domesticated populations through several more or less gradual demographic contractions2,4. As a consequence, the erosion of wild genetic variation5 is typical of modern cultivars, making them highly susceptible to pathogens, pests and environmental change6,7. The loss of genetic diversity hampers further crop improvement programmes to increase food production in a changing world, posing serious threats to food security8,9. Using both ancient and modern seeds, we analysed the temporal dynamics of genetic variation and selection during the domestication process of the common bean (Phaseolus vulgaris) in the southern Andes. Here, we show that most domestic traits were selected for before 2,500 years ago, with no or only minor loss of whole-genome heterozygosity. In fact, most of the changes at coding genes and linked regions that differentiate wild and domestic genomes are already present in the ancient genomes analysed here, and all ancient domestic genomes dated between 600 and 2,500 years ago are highly variable (at least as variable as modern genomes from the wild). Single seeds from modern cultivars show reduced variation when compared with ancient seeds, indicating that intensive selection within cultivars in the past few centuries probably partitioned ancestral variation within different genetically homogenous cultivars. When cultivars from different Andean regions are pooled, the genomic variation of the pool is higher than that observed in the pool of ancient seeds from north and central western Argentina. Considering that most desirable phenotypic traits are probably controlled by multiple polymorphic genes10, a plausible explanation of this decoupling of selection and genetic erosion is that early farmers applied a relatively weak selection pressure2 by using many phenotypically similar but genetically diverse individuals as parents. Our results imply that selection strategies during the past few centuries, as compared with earlier times, more intensively reduced genetic variation within cultivars and produced further improvements by focusing on a few plants carrying the traits of interest, at the cost of marked genetic erosion within Andean landraces.

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This study assessed the concentration, bioconcentration, and bioaccumulation of As, Cd, Co, Cr, Cu, Mg, Mn, Ni, Pb, and Zn in juvenile fishes (Acestrorynchus pantaneiro, Brycon orbygnianus, Cyphocharax voga, Megaleporinus obtusidens, Odontesthes bonariensis, Pimelodus maculatus, Prochilodus lineatus, Salminus brasiliensis, and Schizodon borelli) in the Lower Paraná River (Argentina), the most extensive floodplain from the Plata Basin. The floodplain is crucial for the reproduction and growth of various species such as P. lineatus, M. obtusidens, and S. brasiliensis, which complete their life cycle in this environment. In total, 90 individuals were sampled for nitrogen stable isotope, and trace element analysis in muscle tissue, water, and sediment was analyzed. The results show that all the studied species bioaccumulate Cr, Mg, Ni, and Zn. In particular, B. orbygnianus and P. maculatus presented the highest bioaccumulation factor for Cr. A biodilution of Co through the food chain was observed. No positive correlation was found between element concentration and trophic level, but we observed significant differences between trophic guilds (herbivorous, omnivorous, and carnivorous). Our findings suggest that feeding habits determine trace element concentrations. To establish differential behavior between different species within the aquatic web further studies are necessary, particularly in the floodplain of the Paraná, which is a crucial nursery area for most commercially important fishes from the Plata Basin. Graphical abstract.

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The southern boundary of prehispanic farming in South America occurs in central Mendoza Province, Argentina at approximately 34 degrees south latitude. Archaeological evidence of farming includes the recovery of macrobotanical remains of cultigens and isotopic chemistry of human bone. Since the 1990s, archaeologists have also hypothesized that the llama (Lama glama), a domesticated South American camelid, was also herded near the southern boundary of prehispanic farming. The remains of a wild congeneric camelid, the guanaco (Lama guanicoe), however, are common in archaeological sites throughout Mendoza Province. It is difficult to distinguish bones of the domestic llama from wild guanaco in terms of osteological morphology, and therefore, claims that llama were in geographic areas where guanaco were also present based on osteometric analysis alone remain equivocal. A recent study, for example, claimed that twenty-five percent of the camelid remains from the high elevation Andes site of Laguna del Diamante S4 were identified based on osteometric evidence as domestic llama, but guanaco are also a likely candidate since the two species overlap in size. We test the hypothesis that domesticated camelids occurred in prehispanic, southern Mendoza through analysis of ancient DNA. We generated whole mitochondrial genome datasets from 41 samples from southern Mendoza late Holocene archaeological sites, located between 450 and 3400 meters above sea level (masl). All camelid samples from those sites were identified as guanaco; thus, we have no evidence to support the hypothesis that the domestic llama occurred in prehispanic southern Mendoza.

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The causes of Late Pleistocene megafaunal extinctions (60,000 to 11,650 years ago, hereafter 60 to 11.65 ka) remain contentious, with major phases coinciding with both human arrival and climate change around the world. The Americas provide a unique opportunity to disentangle these factors as human colonization took place over a narrow time frame (~15 to 14.6 ka) but during contrasting temperature trends across each continent. Unfortunately, limited data sets in South America have so far precluded detailed comparison. We analyze genetic and radiocarbon data from 89 and 71 Patagonian megafaunal bones, respectively, more than doubling the high-quality Pleistocene megafaunal radiocarbon data sets from the region. We identify a narrow megafaunal extinction phase 12,280 ± 110 years ago, some 1 to 3 thousand years after initial human presence in the area. Although humans arrived immediately prior to a cold phase, the Antarctic Cold Reversal stadial, megafaunal extinctions did not occur until the stadial finished and the subsequent warming phase commenced some 1 to 3 thousand years later. The increased resolution provided by the Patagonian material reveals that the sequence of climate and extinction events in North and South America were temporally inverted, but in both cases, megafaunal extinctions did not occur until human presence and climate warming coincided. Overall, metapopulation processes involving subpopulation connectivity on a continental scale appear to have been critical for megafaunal species survival of both climate change and human impacts.

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Documents from the 17th Meeting, English and Spanish, are bound together in one volume

Meeting of the Advisory Committee on Medical Research, 17. Pan American Health Organization; 2-5 May 1978

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Documents from the 17th Meeting, English and Spanish, are bound together in one volume

Reunion del Comite Asesor sobre Investigaciones Medicas, 17. Organización Panamericana de la Salud; 2-6 mayo 1978

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