Coastal complexity: Ancient human diets inferred from Bayesian stable isotope mixing models and a primate analogue

Abstract

An extensive ecological literature applies stable isotope mixing models to derive quantitative dietary reconstructions from isotope ratios of consumer tissues. While this approach works well for some organisms, it is challenging for consumers with complex, varied diets, including humans; indeed, many archaeologists have avoided the use of mixing models because uncertainties in model outputs are sufficiently large that the findings are not helpful in understanding ancient lifeways. Here, we exploit an unparalleled opportunity to evaluate the feasibility of dietary quantification in a nutritionally and isotopically complex context on the Cape Peninsula, South Africa. Delta values (δ13C and δ15N) of 213 indigenous food samples enable us to characterise four food groups: terrestrial plants, terrestrial vertebrates, marine invertebrates and marine vertebrates. A recent study of baboons that consumed marine and terrestrial foods provides insight into the relationship between such foods and consumer tissue isotopes. We use this information to refine our interpretation of δ15N and especially δ13C in bone collagen from 35 archaeological hunter-gatherers, achieving better estimates of the relative importance of marine and terrestrial foods in the diet than has hitherto been possible. Based on Bayesian stable isotope mixing model (SIMM) outputs, we infer that the trophic enrichment factor (TEF) for δ13Cbone collagen in these coastal humans is closer to +3 than +5‰. In the most 13C- and 15N-rich individuals, 65–98% of bone collagen (95% credible intervals) derived from marine foods. Conversely, in 13C and 15N-poor individuals, 7–44% of bone collagen derived from marine foods. The uncertainties discussed here highlight the need for caution when implementing SIMMs in studies of consumers with complex diets. To our knowledge, this work constitutes the most detailed and most tightly constrained study of this problem to date.

Diet and adult age‐at‐death among mobile foragers: A synthesis of bioarcheological methods

“…9000 to 500 BP, with a mean antiquity of 2600 BP. Dates are uncalibrated because of the difficulty of accurately determining the precise amounts of marine protein in people's diets (Lewis & Sealy, ; Lewis, West, & O'Riain, ). The presence of this older marine carbon may bias some dates by as much as 200 years (Dewar & Pfeiffer, ; Dewar, Reimer, Sealy, & Woodborne, ).…”

Cost-Benefit Trade-Offs of Aquatic Resource Exploitation in the Context of Hominin Evolution

“…In addition, it also provided evidence for shellfish foraging and for shell tool manufacturing by Homo erectus in Java around 0.5 Ma (Joordens et al, 2015). Nevertheless, reliably determining whether this type of exploitation was opportunistic or not solely from faunal assemblages can be challenging, and scientists must also rely on complementary research methods that allow for dietary reconstruction, such as isotopic analyses (e.g., Lewis and Sealy, 2018). In the Neanderthal site of Vanguard cave, in Gibraltar, for example, while the taphonomic evidence points to the collection, processing and consumption of aquatic resources during the Middle Paleolithic, the absence of isotopic evidence for this behavior-as well as the absence of associated toolssuggests that this practice was opportunistic (Stringer et al, 2008;Richards and Trinkaus, 2009;McLeod, 2018).…”

Shifting Baselines to Thresholds: Reframing Exploitation in the Marine Environment

“…It is not always possible to access baseline trophic web species from past ecosystems, thereby limiting the power of trophic web analysis in the past. However, past dietary analysis using carbon and nitrogen signatures is an established and successful field in historical ecology and biomolecular archeology (Miller et al, 2020;Bird et al, 2021), as well as various other applications, including elucidating cultural thresholds in resource use (Lewis and Sealy, 2018;Nord and Billström, 2018;Miller et al, 2020) and geographic region of origin (Hobson, 1999;Lightfoot and O'Connell, 2016).…”