FRUITS of the sea? A cautionary tale regarding Bayesian modelling of palaeodiets using stable isotope data

Isotopic reconstruction of the subsistence strategy for a Central Italian Bronze Age community (Pastena cave, 2nd millennium BCE)

“…Briefly, the trophic relations are based on a direct correlation between resources and consumers: the latter have higher values than their sources (DeNiro 1985;Schwarcz and Schoeninger 2011). Several diet-to-collagen enrichment factors for both the markers were prompted to interpret the isotopic human diet reconstructions properly via modeling (Ambrose and Norr 1993;Hedges and Van Klinken 2002;Jim et al 2007;O'Connell et al 2012;Fernandes et al 2015;Piliciauskas et al 2017;O'Connell 2017;Halffman et al 2020;Schulting et al 2022), even being aware that δ 13 C and δ 15 N represent complex proxy influenced by trophic position, metabolic and physiological offsets, and environmental factors. To date, the widely accepted diet-collagen offset for humans is 4.8 ± 0.5‰ for δ 13 C and +5.5 ± 0.5‰ for δ 15 N (Schulting et al 2022).…”

How Long was the Mesolithic–Neolithic Overlap in Western Scotland? Evidence from the 4th Millenniumbcon the Isle of Islay and the Evaluation of Three Scenarios for Mesolithic–Neolithic Interaction

“…Carding Mill Bay is a limpet dominated shell midden that has been extensively analysed, involving dating programmes and the isotopic analysis of human remains (Bonsall & Smith 1992;Connock et al 1992;Schulting & Richards 2002;Milner & Craig 2009;Bownes et al 2017;Schulting et al 2022). The midden has been designated as Mesolithic because of bevelled bone artefacts similar to those found in the 5th millennium BC Oronsay shell middens.…”

“…Their dietary inference was challenged, however, by Bownes et al (2017) whose re-analysis using the FRUITS Bayesian modelling software indicated an intake of marine protein at between 15% and 21%. That re-analysis has since been deemed invalid because of methodological errors (Schulting et al 2022). Despite these outstanding but contentious applications of archaeological science, it remains impossible to designate the midden and the skeletal remains as either 'Mesolithic' or 'Neolithic'.…”

“…Schulting and Richards (2002;Richards & Schulting 2006) used isotopic analysis of human remains to argue the Neolithic people had excluded marine foods from their diet, these being a Mesolithic mainstay. Their conclusion has been challenged on methodological grounds (Milner et al 2004), claiming it to be partially incorrect for 'Neolithic' individuals at An Corran (Milner & Craig 2009) and Carding Mill Bay (Bownes et al 2017) but with Schulting et al (2022) arguing the Carding Mill Bay re-analysis is methodologically invalid. Whatever the correct interpretation of the isotopic data, the quantity of samples remains too sparse to make generic statements about Mesolithic and Neolithic diet in the coastal regions of western Scotland, especially for the entire duration of these periods.…”

Isotope analysis in archaeology grand challenge

“…In the case of strontium isotope analysis as a tool for exploring past mobility, there are increasingly intensive discussions about the "best" type of material to sample and ways to best map bioavailable strontium in various contexts and what this means for interpreting movement in the past (Bataille et al, 2020;Holt et al, 2021). Meanwhile, although sometimes criticized (Schulting et al, 2022), Bayesian models, which utilize contextual insights and multi-isotope parameters to try and "rule out" certain interpretive scenarios, are arguably providing more precise estimates of dietary composition and human origins than were possible in the past (Fernandes et al, 2014;Cheung and Szpak, 2022). Modern feeding studies and ecological monitoring of isotopic variability are also showing how other non-traditional isotope systems may provide useful, novel avenues for exploration, including zinc isotope analysis of tooth enamel as a proxy for trophic level (Jaouen et al, 2016;Bourgon et al, 2021).…”