¹³C Content of human collagen as a measure of prehistoric diet in woodland North America

Abstract

PLANTS with the C₄ dicarboxylic acid pathway of photosynthesis have markedly higher ¹³C/¹²C ratios than plants with the C₃ or Calvin pathway^1–4. Cumulative assessments of relative ¹³C concentration (δ¹³C) values for C₃ plant foliage yield an average of −26.5‰, relative to the PDB standard whereas C₄ plants average −12.5‰ (ref. 5). These differences in carbon isotope ratios are passed along the food chain to animals and man, so that the nature of the plant food base can be determined through measurements on different body tissues of the consumers. In this study, the time of introduction of maize, a C₄ plant, to the prehistoric inhabitants of several regions in woodland North America, almost exclusively a C₃ plant regime, was determined through isotopic measurements on human bone collagen. The subsequent elevation of maize to the level of a diet staple is also documented.