Over the past forty years, stable isotope analysis of bone (and tooth) collagen and hydroxyapatite has become a mainstay of archaeological and paleoanthropological reconstructions of paleodiet and paleoenvironment. Despite this method's frequent use across anthropological subdisciplines (and beyond), the present work represents the first attempt at gauging the effects of inter-laboratory variability engendered by differences in a) sample preparation, and b) analysis (instrumentation, working standards, and data calibration). Replicate analyses of a 14C-dated ancient human bone by twenty-one archaeological and paleoecological stable isotope laboratories revealed significant inter-laboratory isotopic variation for both collagen and carbonate. For bone collagen, we found a sizeable range of 1.8‰ for δ13Ccol and 1.9‰ for δ15Ncol among laboratories, but an interpretatively insignificant average pairwise difference of 0.2‰ and 0.4‰ for δ13Ccol and δ15Ncol respectively. For bone hydroxyapatite the observed range increased to a troublingly large 3.5‰ for δ13Cap and 6.7‰ for δ18Oap, with average pairwise differences of 0.6‰ for δ13Cap and a disquieting 2.0‰ for δ18Oap. In order to assess the effects of preparation versus analysis on isotopic variability among laboratories, a subset of the samples prepared by the participating laboratories were analyzed a second time on the same instrument. Based on this duplicate analysis, it was determined that roughly half of the isotopic variability among laboratories could be attributed to differences in sample preparation, with the other half resulting from differences in analysis (instrumentation, working standards, and data calibration). These findings have serious implications for choices made in the preparation and extraction of target biomolecules, the comparison of results obtained from different laboratories, and the interpretation of small differences in bone collagen and hydroxyapatite isotope values. To address the issues arising from inter-laboratory comparisons, we devise a novel measure we term the Minimum Meaningful Difference (MMD), and demonstrate its application.

Bioarchaeology and biogeochemistry can elucidate aspects of individual life histories that are often lost in the archaeological record. Here, we use stable and radiogenic isotope analyses of enamel, bone and hair to reconstruct paleodiet and paleomobility in an adult male interred along a pre-Columbian route connecting the northern Chilean coast to the inland Loa River Valley. Although this well-preserved burial included mortuary goods typical of coastal cultures, it was discovered in a vast, uninhabited part of northern Chile's hyper-arid Atacama Desert. Variation in carbon and nitrogen isotopes reflects dietary differences, while strontium and oxygen isotopes vary geologically and geographically. We use these data to examine paleodiet and paleomobility and to assess whether this was a coastal traveller seeking provisions from the interior or vice versa. Enamel stable isotope analysis is consistent with the consumption of a mixture of terrestrial and marine resources during the first years of life. Bone stable isotope analyses indicate habitual consumption of marine foodstuffs over the last 10-30 years of this individual's life. Interestingly, stable isotope analysis of hair samples provides more finegrained information on this individual, suggesting movements between the coast and highlands in the months before his death. Radiogenic strontium isotope data are consistent with residence on the coast or in the Atacama Desert, but are lower than strontium isotope values from higher altitudes. These dietary and geological patterns are reconcilable with coastal residency; the isotopic data are consistent with foodstuffs and textiles found with the burial. Therefore, we argue that this individual was regularly moving from the coast to inland areas, crossing the hyper-arid Atacama Desert by following strategic interzonal routes that provided access to particular resources.

Indigenous peoples have occupied the island of Puerto Rico since at least 3000 BC. Due to the demographic shifts that occurred after European contact, the origin(s) of these ancient populations, and their genetic relationship to present-day islanders, are unclear. We use ancient DNA to characterize the population history and genetic legacies of precontact Indigenous communities from Puerto Rico. Bone, tooth, and dental calculus samples were collected from 124 individuals from three precontact archaeological sites: Tibes, Punta Candelero, and Paso del Indio. Despite poor DNA preservation, we used target enrichment and high-throughput sequencing to obtain complete mitochondrial genomes (mtDNA) from 45 individuals and autosomal genotypes from two individuals. We found a high proportion of Native American mtDNA haplogroups A2 and C1 in the precontact Puerto Rico sample (40% and 44%, respectively). This distribution, as well as the haplotypes represented, supports a primarily Amazonian South American origin for these populations and mirrors the Native American mtDNA diversity patterns found in present-day islanders. Three mtDNA haplotypes from precontact Puerto Rico persist among Puerto Ricans and other Caribbean islanders, indicating that present-day populations are reservoirs of precontact mtDNA diversity. Lastly, we find similarity in autosomal ancestry patterns between precontact individuals from Puerto Rico and the Bahamas, suggesting a shared component of Indigenous Caribbean ancestry with close affinity to South American populations. Our findings contribute to a more complete reconstruction of precontact Caribbean population history and explore the role of Indigenous peoples in shaping the biocultural diversity of present-day Puerto Ricans and other Caribbean islanders.

The Caribbean was one of the last regions of the Americas to be settled by humans, but how, when, and from where they reached the islands remains unclear. We generated genome-wide data for 93 ancient Caribbean islanders dating between 3200-400 cal. BP and find evidence of at least three separate dispersals into the region, including two early dispersals into the Western Caribbean, one of which seems connected to radiation events in North America. This was followed by a later expansion from South America. We also detect genetic differences between the early settlers and the newcomers from South America with almost no evidence of admixture. Our results add to our understanding of the initial peopling of the Caribbean and the movements of Archaic Age peoples in the Americas.

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The San Salvador River in northern Chile is a tributary of the Loa, the only river that traverses the Atacama Desert from the mountains to the Pacific. Recent investigations along the San Salvador River revealed the presence of a Formative period village site and associated cemetery approximately 110 km inland from the Pacific Ocean. Bioarchaeological and biogeochemical analyses conducted on human skeletal remains recovered from the San Salvador Cemetery allowed us to better understand the site’s role as an intermediary for coast/interior relations during the Middle Formative (500 B.C.–A.D. 100). Evidence from material culture and human remains at San Salvador suggests that this population was involved in exchange networks that united the oases of the Atacama Desert with the Pacific Ocean. Isotopic data support this notion, as the population demonstrates great variability in both the protein (marine and terrestrial) and carbohydrate components of their diet. During this period, communal economies produced surpluses used in a network of exchange for foods, prestige goods, and ideas. These ties were not coincidental but, rather, part of a regional economic structure that remains only partly explored.

In recent years, a debate about the degree to which prehistoric fishing practices may, or may not, have adversely impacted local fish communities has re-emerged in the Caribbean archaeological and fisheries literature. Through carbon and nitrogen stable isotope analyses of radiocarbon dated human skeletal remains from southeastern Puerto Rico, the present work identifies a significant (one to two trophic level) decline in the mean trophic level of human-consumed fish over a period of six centuries (fifth-eleventh centuries AD). While the extrapolation of such results to a pan-Caribbean scale would be foolhardy, this work provides complementary evidence that, at least on a local scale, fishing pressure brought to bear by prehistoric peoples may have had the capability to "fish down" marine food webs in a manner akin to that seen in many global fisheries in more recent years.

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