The center cannot hold: A Bayesian chronology for the collapse of Tiwanaku.

The timing of Tiwanaku's collapse remains contested. Here we present a generational-scale chronology of Tiwanaku using Bayesian models of 102 radiocarbon dates, including 45 unpublished dates. This chronology tracks four community practices: residing short- vs. long-term, constructing monuments, discarding decorated ceramics, and leaving human burials. Tiwanaku was founded around AD 100 and around AD 600, it became the region's principal destination for migrants. It grew into one of the Andes' first cities and became famous for its decorated ceramics, carved monoliths, and large monuments. Our Bayesian models show that monument building ended ~AD 720 (the median of the ending boundary). Around ~AD 910, burials in tombs ceased as violent deaths began, which we document for the first time in this paper. Ritualized murders are limited to the century leading up to ~AD 1020. Our clearest proxy for social networks breaking down is a precise estimate for the end of permanent residence, ~AD 1010 (970-1050, 95%). This major inflection point was followed by visitors who used the same ceramics until ~AD 1040. Temporary camps lasted until roughly ~AD 1050. These four events suggest a rapid, city-wide collapse at ~AD 1010-1050, lasting just ~20 years (0-70 years, 95%). These results suggest a cascading breakdown of community practices and social networks that were physically anchored at Tiwanaku, though visitors continued to leave informal burials for centuries. This generation-scale chronology suggests that collapse 1) took place well before reduced precipitation, hence this was not a drought-induced societal change and 2) a few resilient communities sustained some traditions at other sites, hence the chronology for the site of Tiwanaku cannot be transposed to all sites with similar material culture.

Paleopathology and children in the Andes: Local/situated biologies and future directions.

In the decades since Verano (1997) published his foundational piece on Andean paleopathology, scholars have recognized the importance of the bioarchaeology of childhood. Yet, scholarship on ancient childhood in the Andes deemphasizes paleopathology. Nonadult paleopathological data are often employed in large-scale, biocultural studies focused on environmental or political adaptations; however, they can also elucidate children's individual lived experiences and roles in society. To generate culturally-meaningful paleopathological data, we must take a contextualized approach to our analyses and interpretations. Disparate use of chronological age in published datasets makes synthesis across studies problematic, and ethnohistorical and ethnographic data on Andean children demonstrate that developmental age categories, rather than chronological age ranges, are most appropriate. Further, paleopathological data can best inform our investigations when they are combined with related datasets such as those on sex, diet, activity, and mobility. With that in mind, we use the theoretical framework of "local biologies" (and the related "situated biologies"), where biology is viewed as heavily contingent on culturally-specific beliefs and practices and local physical, sociocultural, and political environments (Lock, 1993, 2001; Niewöhner and Lock, 2018). Local biologies approaches can enrich social bioarchaeology and paleopathology to by specifically situating children and their experiences within the ancient Andean world.

Why are rare traits unilaterally expressed?: trait frequency and unilateral expression for cranial nonmetric traits in humans.

Based on an analysis of nonmetric trait databases from several large skeletal series in Northern Europe and South America, representing 27 bilateral traits, we report a predictable relationship between the frequency of nonmetric traits and the probability that they are expressed bilaterally. In a wider sampling of traits and populations, this study thus confirms the findings of an earlier study by Ossenberg ([1981] Am. J. Phys. Anthropol. 54:471-479), which reported the same relationship for two mandibular traits. This trend was previously explained by extending the multifactorial threshold model for discontinuous traits to incorporate either separate thresholds for unilateral or bilateral expression, or by a fuzzy threshold in which the probability of bilateral expression increases away from the median threshold value. We show that the trend is produced under the standard multifactorial threshold model for discontinuous traits simply if the within-individual or developmental instability variance remains relatively constant across the range of liability. Under this assumption, the number of individuals in which one side but not the other is pushed over the threshold for trait formation will be a larger proportion of the number of individuals expressing the trait when the trait frequency is low. As trait frequency increases, the significance of within-individual variance as a determinant of trait formation decreases relative to the genetic and among-individual environmental variance. These results have implications for interpreting nonmetric trait data as well as for understanding the prevalence of unilateral vs. bilateral expression of a wide variety of discontinuous traits, including dysmorphologies in humans.

Anemia and childhood mortality: latitudinal patterning along the coast of pre-Columbian Peru.

Hrdlicka ([1914] Smithson. Inst. Misc. Collect. 61:1-69) reported that pre-Columbian skeletal material from the coastal lowland Andean region exhibited a high frequency of porotic hyperostosis, a pathological condition of bone that generally is thought to indicate childhood anemia. While subsequent studies tended to reinforce this conclusion, factors implicated in the condition have yet to be fully explored in the region as a whole. This study explores regional and intravalley variation as one step in establishing biocultural variables that increase the apparent risk of childhood anemia. The study sample includes 1,465 individuals: 512 from Peruvian collections housed at the Field Museum of Natural History, and 953 from systematically excavated contexts from Moquegua, Peru. Environmental stressors, such as parasites and disease, rather than specific dietary practices were found to be more likely associated with childhood anemia in these coastal Andean samples. The study supports cribra orbitalia as an earlier expression of porotic hyperostosis and suggests that porotic hyperostosis, as recorded here, cannot be easily dismissed as a result of cranial shape modification. No clear temporal patterns were observed. Finally, the study establishes that comparing data for children and adults can reveal the relative association between childhood anemia and mortality. Childhood mortality associated with anemia was elevated where the presence of tuberculosis or tuberculosis-like conditions was more common and the presence of water-borne pathogens was negligible. In contrast, those buried at lower altitudes, closer to the coast, and consuming mainly marine resources were less likely to die in childhood with anemia than in the other contexts studied.