Sensitivity of bulk sedimentary stable carbon isotopes to prehistoric forest clearance and maize agriculture

The stable carbon isotope compositions (δ¹³C) of tropical lake sediments and soils have been used to reconstruct the occurrence of prehistoric maize cultivation and its relative importance through time. This study assesses some of the possible variables affecting the response of lake sediment bulk organic carbon isotope (δ¹³C_TOC) values to variations in the scale of prehistoric maize cultivation and the potential of this proxy to yield quantitative estimates of the scale of prehistoric maize agriculture in small tropical watersheds. High resolution analyses of δ¹³C_TOC values, maize pollen concentrations, and mineral influx were conducted on sediments deposited during a ∼220 year period of prehistoric maize agriculture in the watershed of Laguna Castilla, a small lake in the mid-elevations of the Cordillera Central, Dominican Republic. Close correspondence between δ¹³C_TOC values and maize pollen concentrations in the Laguna Castilla sediment record indicates a close relationship between the isotopic values and the scale of prehistoric maize cultivation. Correlations between the δ¹³C_TOC signature and mineral influx indicate that the isotope record is also sensitive to variations in allochthonous carbon delivery. This study establishes that sedimentary δ¹³C_TOC values can provide a highly sensitive proxy of the spatial scale of prehistoric maize agriculture in small tropical watersheds, but emphasizes the need for a better understanding of sediment dynamics and carbon cycling in anthropogenically modified landscapes before this proxy can be widely employed in diverse archaeological settings.     

Discriminant function analyses in archaeology: are classification rates too good to be true?

The use of discriminant function analyses (DFA) in archaeological and related research is on the increase, however many of the assumptions of this method receive a mixed treatment in the literature. Statisticians frequently use complex statistical models to investigate analytical parameters, but such idealised datasets may be hard to relate to “real-life” examples and the literature difficult to assess. Using two faunal datasets that are more typical of archaeological and related research, one comprised of size-corrected linear measurements of bovid humeri and another of 3D geometric morphometric (GMM) shape data of African monkey skulls, and two simulated datasets, we illustrate some of the most important but often ignored issues of DFA. We specifically show why it is paramount to address “over-fitting” by cross-validation when applying this method and how the probability of correctly classifying cases by chance can be properly and explicitly taken into account.     

Molecular evidence of changing foodways across the Mississippian transition at the George Reeves site (11S650)

ABSTRACT

The George Reeves site (11S650) is a multicomponent village on the bluffs in the central American Bottom, Illinois. The site was occupied from the Late Woodland Rosewood phase through the Mississippian Lohmann phase. Pottery use and dietary variation between the Late Woodland and Emergent Mississippian occupations at the site were explored through stylistic analysis, pottery residue analysis, and compound-specific carbon isotopic analysis of pottery residues. Although more samples should be analyzed, diet and pottery use at George Reeves seems to have been varied, with maize present by cal AD 900–1000, but comprising a relatively small portion of lipid residues in pottery. Residue analysis indicates a C₄ presence in 5 of 16 sampled pots from the early Emergent Mississippian deriving from either maize or from meat from animals consuming maize. Pottery residues were mixed, showing C₃ and C₄ plants as well as meat and fish or shellfish. One residue showed a high incidence of C₄ contribution, most likely from Portulaca oleracea (common purslane), as well as large amounts of fish or shellfish and another C₃ plant. Residue from a ceramic pipestem indicates that maize may have been smoked, probably in the form of maize silk mixed with other nontobacco plants.     

Alternative pathways to power in late Postclassic Highland Mesoamerica

In recent years, scholars have become dissatisfied with neoevolutionists’ view of social evolution as a series of step-like transformations leading to political centralization and have refocused attention away from traditional theory and toward issues of agency, power sharing, and alternative pathways to complexity. To build on this emerging theoretical orientation, we propose that collective action theory provides a useful path to explaining social change. To evaluate this idea, we make use of ethnohistoric and archaeological sources on the Postclassic (AD 1250–1521) of Highland Mesoamerica (Central Highlands of Mexico and the Mixteca Alta region of Oaxaca), to investigate the causes and consequences of key aspects of sociopolitical change. Of the study states, Tlaxcallan, Cholula, Texcoco, and other central Highlands polities relied extensively on internal revenues and, accordingly, implemented power sharing, control of political officials, and infrastructural power. Conversely, states in eastern Puebla and the Mixteca Alta focused on external revenues and, thus, exhibited greater degrees of despotic governance. These results suggest that collective action provides a useful starting point for understanding state-building in Highland Mesoamerica and merits further testing with other Mesoamerican cases as well as societies in other world areas.