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

史前大量食用海洋食物的最显著的考古证据是在世界许多地方的贝壳堆中观察到的，那里经常可以看到数百万被丢弃的软体动物贝壳。食用其他海洋食品的证据要难得多。例如，鱼骨往往又小又脆弱，在许多地点不能很好地生存，而海洋哺乳动物的尸体很可能已经被处理到远离定居点的地方。此外，钓鱼用具，如钩子、长矛、下沉器、陷阱、网、船等都是相当罕见的发现。总的来说，史前人类开发水生资源的物质证据比其他粮食采购活动（如农业）要少得多，因此必须寻找其他证据来源。评估海洋资源消耗最广泛使用的方法是利用“人如其食原则”对人类骨骼进行稳定同位素分析。该方法利用了这样一个事实，即海洋和陆地来源的食物具有不同的稳定同位素值，这些同位素值记录在食用特定饮食的人的骨骼生化物质中。人类骨骼中同位素信息的主要来源是结构蛋白胶原蛋白，它在许多考古遗址中保存得很好。在20世纪80年代早期，对来自丹麦的中石器时代狩猎采集者和新石器时代农民骨骼的分析表明，从大量食用海洋食物到以陆地为食的饮食发生了急剧转变。最近的研究为人类史前这一关键时期的饮食变化提供了进一步的证据。然而，这项工作引起了相当大的兴趣，因为稳定同位素证据表明饮食中蛋白质含量很高。此外，生活在沿海地区的新石器时代早期农民完全放弃海鲜消费是非常重要的。尽管这些稳定同位素方法已经应用了三十多年，但人们对海洋同位素信号在人骨胶蛋白中表达的生化和代谢控制尚缺乏了解。我们的建议是由一种信念刺激的，即胶原蛋白的稳定同位素组成需要在单个氨基酸的水平上被理解。事实上，我们小组最近对南非史前人类的研究，采用了一种特定化合物的碳同位素方法，揭示了一种新的海洋饮食指标，从而强调了采用这种方法的潜在收益。该研究项目旨在通过了解支撑胶原蛋白稳定同位素信号的生化和营养因素，解决史前人类对海洋食物消费的检测这一基本问题。这将通过以下方式实现：(i)开发一种新的分析方法，允许在构建块氨基酸水平上对胶原蛋白进行常规稳定的碳同位素分析，从而获得比仅分析整个胶原蛋白更详细的同位素信息；对可能被古代人类吃掉的海洋和陆地生物的生化成分进行稳定同位素分析。这些数据将用于发展基于生物化学的理解，了解海洋食物的同位素值最终在人体组织中被记录的方式，以及（iii）进行动物喂养实验，其中猪将被用作人类的代谢类似物。这些猪将被饲喂不同海洋和陆地蛋白质含量的饲粮，这样所获得的成分和稳定同位素数据可用于构建数学模型，由此确定骨骼生化物质稳定同位素值的生化和代谢控制。我们通过上述研究获得的进一步了解将用于解释欧洲和非洲史前人类海洋食物消费的趋势。

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.