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Isotope ratio analyses of trace elements are applied to tooth enamel, ostrich eggshell, and other archaeological hard tissues to infer mobility and other aspects of hominin and animal paleoecology. It has been assumed that these highly mineralized tissues are resistant to diagenetic alteration, but this is seldom tested and some studies document diagenetic alteration over brief time spans. Here, we build on existing research on Maximum Threshold Concentrations (MTCs) to develop screening tools for diagenesis that can inform heavy isotopic analyses. The premise of the MTC approach is that archaeological tissues are likely contaminated and unsuitable for isotope ratio analysis when they exceed characteristic modern concentration ranges of trace elements. Furthermore, we propose a new metric called the Maximum Threshold Ratio (MTR) of 85Rb/88Sr or whole element Rb/Sr, which can be measured simultaneously with 87Sr/86Sr during laser ablation (LA) MC-ICP-MS or applied during post hoc screening of specimens. We analyzed 56 enamel samples from modern Kenyan mammals and 34 modern ostrich eggshells from South Africa, Namibia, and the United States by solution ICP-MS, as well as a subset of shells using LA-MC-ICP-MS. Our results indicate that thresholds are consistent across taxa at a single location, but likely vary across locations. Therefore, MTCs and MTRs need to be tissue and locality specific, but not necessarily taxon-specific. Other important differences are observed between the inner and outer surfaces of the eggshells and between LA and solution ICP-MS. This exploratory study provides guidelines for building reference thresholds to screen enamel and eggshell for diagenesis potentially impacting biogenic isotope ratios. 

Money has been portrayed by major theorists as an agent of individualism, an instrument of freedom, a currency that removes personal values attached to things, and a generator of avarice. Regardless, the impact of money varies greatly with the cultural turf of the recipient societies. For traditional subsistence economies based on gifting and sharing, surplus perishable resources foraged from the environment carry low costs to the giver compared with the benefits to the receiver. With cash, costs to the giver are usually the same as benefits to the receiver, making sharing expensive and introducing new choices. Using quantitative data on possessions and expenditures collected over a 44-y period from 1974 to 2018 among the Ju/’hoansi (!Kung) in southern Africa, former hunter-gatherers, we look at how individuals spend monetary income, how a partial monetary economy alters traditional norms and institutions (egalitarianism, gifting, and sharing), and how institutions from the past steer change. Results show that gifting declines as cash is spent to increase the well-being of individual families and that gifting and sharing decrease and networks narrow. The sharing of meals and casual gifting hold fast. Substantial material inequalities develop, even between neighbors, but social, gender, and political equalities persist. A strong tradition for individual autonomy combined with monetary income allows individuals to spend their money as they choose, adapt to modern conditions, and pursue new options. However, new challenges are emerging to develop greater community cooperation and build substantial and sustainable economies in the face of such centrifugal forces.