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

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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.