Calcium isotopes: a new tool to study the spread of dairying in prehistory

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This project is to apply a new way of analysing bone, in order to learn how milk, and dairying generally, became so important in Western human diet. Our food has been profoundly changed by two 'revolutions'; the invention of agriculture starting about 10,000 years ago, and of industrial scale food production, starting about 100 years ago. Milk and its products remains a very important part of our diet, and also provides our major source of calcium, but this is true only for the people and areas where it was developed in prehistoric times (in Europe, India, and parts of Africa, but not, e.g. in China, America, or Oceania). So we are focussing on the Neolithic period, the cultural epoch of the discovery and spread of agriculture in Europe. Some evidence already exists for dairying during the Neolithic (from pottery remains and from animal bones), but we do not know how nutritionally or economically important it was or became. We do know that with agriculture, the Neolithic saw great demographic growth, leading to social change and the rise of towns; and we also know that milk consumption was biologically important enough for Europeans to become genetically selected for the ability to digest lactose after infancy. Our method depends on measuring the abundance ratio of the calcium isotopes found in nature. As calcium flows through food chains, its distinctive isotope ratio can be used as a tracer. We have very recently shown that calcium in milk has a small but clearly different isotope ratio from other local dietary sources of calcium (mainly from plants); and our results on a small number of archaeological bones confirms that this difference shows up in Neolithic and later human bones where dairying seems likely, but not in earlier bones. The next step is to test the method very much more widely, understand its strengths and limitations, and learn how best to apply it to quantifying how dairying impacted on human diet and nutrition during prehistory. We then can make a proper study of milk consumption on several sites, and relate this to other types of dietary information from them (e.g. of types of protein consumption). We also want to investigate the potential of applying calcium isotope measurements beyond this main study, to such related issues as learning about the timing of nursing and weaning (the method applies to taking in maternal milk as well as farmed animal milk), as this also can tell us about the influences for human population growth. An exciting prospect is that it might be applicable to studying the development of Early Man in Africa . Other plans include seeing if the method works for cremated bone, as these are the main remains at some periods.