Marine Resource Exploitation and Consumption Amongst Ancient Human Populations: Unravelling the Stable Carbon Isotope Signal of Bone Collagen

Lead Research Organisation: University of Bristol
Department Name: Chemistry


The most striking archaeological evidence for extensive marine food consumption in prehistory is observed in shell middens seen in many parts of the world, where many millions of discarded shells of molluscs are often evident. Evidence for the consumption of other marine foods is much less readily obtained. For example, fish bones are often small and fragile and do not survive well at many sites, while the carcasses of marine mammals would likely have been processed away from settlements. Moreover, fishing paraphernalia such as hooks, spears, sinkers, traps, nets, boats, etc. are rather rare finds. Overall, the material evidence for the exploitation of aquatic resources by prehistoric humans is much rarer than for other food procurement activities, such as farming, hence other sources of evidence must be sought. The most widely used approach to assessing marine resource consumption has been to employ stable isotope analysis of human bones using the 'you are what you eat principle'. The approach draws on the fact that ocean and land derived foods have different stable isotope values that are recorded in the bone biochemicals of the people eating given diets. The major source of isotopic information in human bones is the structural protein collagen, which survives well at many archaeological sites. In the early 1980s analyses of the skeletons of Mesolithic hunter-gatherers and Neolithic farmers from Denmark suggested a sharp shift from high marine food consumption to terrestrial-based diets. More recent work has provided further evidence for this diet change at this key time in human prehistory. However, this work has raised considerable interest because of the high levels of protein in the diet suggested by the stable isotope evidence. Moreover, the complete abandonment of seafood consumption by Early Neolithic farmers living in coastal areas is highly significant. Despite more than thirty years of application of these stable isotope methods there is a lack of understanding of the biochemical and metabolic controls on the expression of the marine isotope signal in human bone collagen. Our proposal is stimulated by a belief that the stable isotope composition of collagen needs to be understood at the level the individual amino acids. Indeed recent work on prehistoric humans from South Africa by our group, employing a compound-specific carbon isotope approach, revealed a new marine dietary indicator, thereby emphasising the potential gains of employing such an approach. This research project seeks to address the fundamental question of the detection of marine food consumption by prehistoric humans by developing an understanding of the biochemical and nutritional factors that underpin the stable isotope signals of collagen. This will be achieved by: (i) Developing a new analytical approach that will allow routine stable carbon isotopic analysis of collagen at the level of the building block amino acids, thereby allowing access to more detailed isotopic information than can be obtained by analysing only whole collagen; (ii) Undertaking stable isotope analyses of the biochemical components of marine and terrestrial organisms likely to have been eaten by ancient humans. These data will be used to develop a biochemically-based understanding of the way in which the isotopic values of marine foods are ultimately recorded in human tissues, and (iii) Undertake an animal feeding experiments in which pigs will be used as metabolic analogues for humans. The pigs will be fed on diets varying in marine and terrestrial protein content such that the compositional and stable isotope data obtained can be used to construct mathematical models from which the biochemical and metabolic controls on the stable isotope values of bone biochemicals will be determined. The enhanced understanding we obtain through the above research will be used to explain trends in marine food consumption by prehistoric humans in Europe and Africa.


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Webb E (2017) Sulphur-isotope compositions of pig tissues from a controlled feeding study in STAR: Science & Technology of Archaeological Research

Description The research was successful in three areas.

Methodological developments: This involved a comparison of the amino acid (AA) d13C values obtained by gas chromatography-combustion-isotope ratio mass spectrometry (GC/C/IRMS) and liquid chromatography-isotope ratio mass spectrometry (LC/IRMS). Although the primary focus was the compound-specific stable carbon isotope analysis of bone
collagen AAs, because of its growing application for palaeodietary and palaeoecological reconstruction, the results
are relevant to any field where AA d13C values are required. We compared LC/IRMS with the most up-to-date
GC/C/IRMS method using N-acetyl methyl ester (NACME) AA derivatives. This comparison involved the analysis
of standard AAs and hydrolysates of archaeological human bone collagen, which have been previously investigated
as N-trifluoroacetyl isopropyl esters (TFA/IP). It was observed that, although GC/C/IRMS analyses required less
sample, LC/IRMS permitted the analysis of a wider range of AAs, particularly those not amenable to GC analysis
(e.g. arginine). Accordingly, reconstructed bulk d13C values based on LC/IRMS-derived d13C values were closer to
the EA/IRMS-derived d13C values than those based on GC/C/IRMS values. The analytical errors for LC/IRMS AA
d13C values were lower than GC/C/IRMS determinations. Inconsistencies in the d13C values of the TFA/IP
derivatives compared with the NACME- and LC/IRMS-derived d13C values suggest inherent problems with the
use of TFA/IP derivatives, resulting from: (i) inefficient sample combustion, and/or (ii) differences in the intramolecular
distribution of d13C values between AAs, which are manifested by incomplete combustion. Close similarities between the NACME AA d13C values and the LC/IRMS-derived d13C values suggest that the TFA/IP derivatives should be abandoned for the natural abundance determinations of AA d13C values.

Understanding macronutrient carbon flow from diet to pig tissues: In recent years, it has become increasingly evident that severe limitations exist in our ability to meaningfully assess human palaeodiet using stable isotope compositions. These limitations in part arise because many of the fundamental assumptions about tissue-diet relationships are poorly understood. In order to redress this deficiency, a controlled feeding experiment was undertaken in this project to define the impact of terrestrial- vs. marine-derived dietary protein consumption on consumer tissue isotopic compositions. We succeeded in elucidating tissue-tissue and tissue-diet carbon isotopic discriminations under different conditions of dietary protein consumption. Two generations of pigs were raised on one of five feeds with varying proportions of terrestrial (soy) and marine (fish meal) protein. A comprehensive range of bone, soft tissues and fluids from 49 pigs, including collagen, muscle, liver, hair, milk, blood, plasma and feces, was submitted to stable carbon-isotope analysis. The observed tissue-whole diet and tissue-dietary protein carbon isotopic offsets were found to be highly dependent on the percentage of marine protein in diet. Preliminary amino acid carbon-isotope compositions suggest that the trend in stable carbon-isotope offsets most likely derives from the increased routing of non-essential amino acids with the increasing proportion of marine protein in the diet. These findings demonstrate that solely using bulk stable carbon isotopic compositions not only masks considerable information about diet, but may also lead to erroneous representations of marine and terrestrial resource consumption in the past.

Applications to archaeological populations: (i) Of central importance to palaeodietary reconstruction is a clear understanding of relative contributions
of different terrestrial (i.e., C3 vs. C4 plants) and aquatic (i.e., freshwater vs. marine) resources to human diet. There are, however, significant limitations associated with the ability to reconstruct palaeodiet using bulk collagen stable isotope compositions in regions where diverse dietary resources are available. Recent research has determined that carbon-isotope analysis of individual amino acids has considerable
potential to elucidate dietary protein source where bulk isotopic compositions cannot. Using d13CAA
values for human and faunal remains from Zvejnieki, Latvia (8th e 3rd millennia BCE), we tested several isotopic proxies focused on distinguishing freshwater protein consumption from both plant-derived and marine protein consumption. We determined that the D13CGly-Phe and D13CVal-Phe proxies can effectively discriminate between terrestrial and aquatic resource consumption, and the relationship between
essential d13CAA values and the D13CGly-Phe and D13CVal-Phe proxies can differentiate among the four protein consumption groups tested here. Compound-specific amino acid carbon-isotope dietary proxies thus enable an enhanced understanding of diet and resource exploitation in the past, and can elucidate complex dietary behaviour.

(ii) Compound-specific amino acid carbon-isotope compositions have shown particular promise for elucidating dietary behaviors in complex environmental contexts, and may also be able to mitigate the effect of many of the limitations
inherent to palaeodietary reconstructions. We investigated the efficacy of compound-specific amino acid isotopic proxies in characterizing the consumption of different dietary protein sources using amino acid carbon isotope compositions for humans and fauna from Rössberga (Early to Middle
Neolithic), Köpingsvik (Mesolithic and Middle Neolithic), and Visby (Medieval Period), Sweden. We also assessed the explanatory capabilities of an isotopic mixing model when used with essential amino acid carbon-isotope
compositions of humans and local fauna. All three isotopic proxies distinguished among humans from the three sites consistently and informatively, and were able to enhance the broad interpretations made using bulk isotopic compositions. The mixing model palaeodietary reconstruction revealed considerable diversity in relative protein source contributions among individuals at both Köpingsvik and Visby. Comparing the mixing model for bulk carbon- and nitrogen-isotope compositions to the model for essential amino acid isotopic compositions further demonstrated the likelihood of
under estimation and overestimation of marine protein consumption for both aquatic-dominant and mixed marine-terrestrial diets when using bulk isotopic compositions.
Exploitation Route The tissues of the pigs raised in the this project are being used in a further NERC grant currently in progress investigating nitrogen metabolism. The tissues have also been used by two PhD projects that are also in progress.
Sectors Agriculture, Food and Drink,Environment,Culture, Heritage, Museums and Collections

Description Historical England ORA Training Day St Luke's Communityr Centre, London 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact Training event to introduce an archaeological guidance manual to archaeological practitioners. Event sparked discussion and questions afterwards.
Year(s) Of Engagement Activity 2017
Description Historical England ORA Training Day, Bristol 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact The training event was to introduce an archaeological guidance manual to archaeological practitioners. 60 plus people attend from Historical England. The training sparked questions and discussions afterwards.
Year(s) Of Engagement Activity 2017