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Stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of bone collagen has become a cornerstone method for reconstructing the diets of past populations. This critical review moves beyond the mere presentation of data to examine the theoretical foundations, methodologies, and applications of this approach. The principles of the method are based on isotopic fractionation during photosynthetic pathways (C3, C4, and CAM) and the trophic-level enrichment of 15N, which together enable the differentiation of plant food sources and the identification of consumer trophic position, respectively. The methodology encompasses sampling strategies, challenges posed by diagenesis, collagen extraction protocols, including the Longin method, and quality-control criteria (collagen yield, C:N ratio). Key applications include the reconstruction of baseline diets, the determination of weaning practices, and the identification of social inequalities. However, confounding factors—such as climate-driven variation in baseline nitrogen values, physiological effects (disease, lactation), and the consequences of human activities (manuring)—can complicate interpretation. Future directions include compound-specific amino acid analysis, multi-isotope approaches, and Bayesian modelling. In conclusion, isotopic data require a contextual and interdisciplinary approach to achieve a realistic understanding of diet and socio-cultural dynamics during the Quaternary.
Koochakzaei et al. (Mon,) studied this question.