نکاتی در خصوص ایزوتوپ ها و استخوان های قدیمی On Isotopes And Old Bones

INTRODUCTION The application of stable light isotope ratio analysis to past human diets has by now reached a certain level of maturity. It is over 30 years since the first pioneering publications appeared reporting the application of stable carbon isotopes to the uptake of maize amongst prehistoric woodland Americans (Vogel and van der Merwe 1977; van der Merwe and Vogel 1978). These first elegant applications built on a series of discoveries related to carbon isotope pathways in plant photosynthesis (e.g., Smith and Epstein 1971), the observations and experience garnered by radiocarbon chemists (e.g., Berger et al. 1964; Tamers and Pearson 1965; Bender 1968; Longin 1971; Hassan and Ortner 1977), and then controlled diet experiments (DeNiro and Epstein 1978) and observations from free-ranging animals (Vogel 1978) that provided the essential information about transfer of dietary isotope composition to animals’ tissues. The distinct advantage of a stable isotope natural abundance approach for dietary studies is that it reflects the foods actually eaten by an individual, or a group of individuals, rather than a palimpsest of waste of uncertain duration that typically preserves only a tiny fraction of the original material and overlooks those organic remains with low survival rates, such as plant foods. In the North American case, the results were decidedly unexpected, and prompted a re-examination of the earlier archaeological evidence for the formation of complex societies, and the adoption and spread of maize agriculture. They also prompted a longstanding debate about how much maize was reflected in the collagen isotope values, and the broader debate around this issue still permeates isotope dietary studies. The main challenges are about what the isotopic composition of various human tissues really means in terms of quantifiable dietary components—whether there is over- or under-representation, how we deal with issues of equifinality and variability, and whether the measured isotopic values have remained intact over the passage of time. We need to understand how post mortem processes may impact on the primary dietary information. These problems were posed early on and, in spite of clear advances, a significant number of the challenges are still current today. As part of Archaeometry’s 50th anniversary year, we were asked to chart the course of our field over the past half century or so, paying particular attention to the contributions that have appeared in this journal. Because the fundamental developments of stable light isotope ecology have taken place within many disciplines, the pioneering studies are scattered across an extremely wide literature, from geochemistry (the original ‘home’ discipline), to plant and animal sciences, archaeology and general science. This journal has published pioneering studies on the application of stable light isotope ratio analysis to Classical marbles in the Mediterranean (e.g., Herz 1992), but contributions in isotope applications to palaeodiets have tended rather to be directed at the issues of preservation of calcified tissues. In particular, a special 2002 issue of Archaeometry was devoted to the Fourth Bone Diagenesis meeting. For the purposes of this review, I have concentrated on the most fruitful major dietary applications, and on charting the subsequent progress in addressing the major issues that have arisen out of these studies. As alluded above, they include the issues of interpretation of quantity (how much), routing of dietary nutrients (how representive), and diagenesis in different tissues (how reliable are the analyses of bone and enamel, organic and inorganic components). Because of the breadth of the field, I confine the review to a few exemplary studies, including the adoption of maize agriculture, marine-focused diets amongst coastal hunter–gatherers, trophic level amongst Glacial-period modern humans and Neanderthals, and the use of savannah resources by early hominins in Africa. Finally, I provide some pointers to the directions in which the field is heading, including high-resolution life history applications. As a start, it is useful to consider the main principles of stable light isotopes in foodwebs, and issues of preservation and quality control, before we consider specific applications to human diets.