Experimental assessment of the impact of food processing on δ15N values in dietary meat – Implications for paleodietary reconstruction

Abstract

Stable isotope studies of bone collagen are widely applied in an attempt to understand the history and range of modern human and earlier hominin diets. The nitrogen isotope system has been extensively applied to the human bioarchaeological record to predict dietary protein sources, as nitrogen isotope ratios roughly track the trophic positionality of an organism. While the ratio of nitrogen isotopes in organisms (δ¹⁵N) tends to be reflective of trophic position, nitrogen isotope fractionation is complex and subject to many sources of variation. This study explores how human behavior might influence this variation. We experimentally investigated the impact of food-related behaviors on the δ¹⁵N dietary proxy, with specific focus on selection and processing of animal food sources. In assessing putrefaction, processing, prey choice, and fuel wood, we saw that these variables generated small shifts of ∼1.5‰ or less in the δ¹⁵N values of food items. We conclude that scavenging as a frequent dietary adaptation may be isotopically visible, but the timing of carcass scavenging likely matters. We also posit that prey species and fuel wood species might matter for the patterning of δ¹⁵N shifts produced by different types of cooking. The results of this study expand the range of contributing factors to consider when utilizing the nitrogen isotope dietary proxy and open new testable questions about the use of this method in populations where complex food behavior may be common.