Documenting the diet in ancient human populations through stable isotope analysis of hair

Fundamental to the understanding of human history is the ability to make in terpretations based on artefacts and other remains which are used to gather information about an ancient population. Sequestered in the organic matric es of these remains can be information, for example, concerning incidence o f disease, genetic defects and diet. Stable isotopic compositions, especial ly those made on isolates of collagen from bones, have been used to help su ggest principal dietary components. A significant problem in the use of col lagen is its long-term stability, and the possibility of isotopic alteratio n during early diagenesis, or through contaminating condensation reactions. In this study we suggest that a commonly overlooked material, human hair, may represent an ideal material to be used in addressing human diets of anc ient civilizations. Through the analysis of the amino-acid composition of modern hair, as well as samples that were subjected to radiation (thus simulating ageing of the hair) and hair from humans that is up to 5200 years old, we have observed l ittle in the way of chemical change. The principal amino acids observed in all of these samples are essentially identical in relative abundances and c ontent. Dominating the compositions are serine, glutamic acid, threonine, g lycine and leucine, respectively accounting for approximately 15%, 17%, 10% , 8% and 8% of the total hydrolysable amino acids. Even minor components (f or example, alanine, valine, isoleucine) show similar constancy between the samples of different ages. This constancy clearly indicates minimal altera tion of the amino-acid composition of the hair. Further, it would indicate that hair is well preserved and is amenable to isotopic analysis as a tool for distinguishing sources of nutrition. Based on this observation, we have isotopically characterized modern indivi duals for whom the diet has been documented. Both stable nitrogen and carbo n isotope compositions were assessed, and together provide an indication of trophic status, and principal type (C-3 or C-4) of vegetation consumed. Tr ue vegans have nitrogen isotope compositions of about 7 parts per thousand whereas humans consuming larger amounts of meat, eggs, or milk are more enr iched in the heavy nitrogen isotope. We have also analysed large cross-sect ions of modern humans from North America and Europe to provide an indicatio n of the variability seen in a population (the supermarket diet). There is a wide diversity in both carbon and nitrogen isotope values based at least partially on the levels of seafood, corn-fed beef and grains in the diets. Following analysis of the ancient hair, we have observed similar trends in certain ancient populations. For example, the Coptics of Egypt (1000 BP) an d Chinchorro of Chile (5000-800 BP) have diets of similar diversity to thos e observed in the modern group but were isotopically influenced by local nu tritional sources. In other ancient hair (Egyptian Late Middle Kingdom mumm ies, ca. 4 000 BP), we have observed a much more uniform isotopic signature , indicating a more constant diet. We have also recognized a primary vegeta rian component in the diet of the Neolithic Ice Man of the Oetztaler Alps ( 5200 BP). In certain cases, it appears that sulphur isotopes may help to fu rther constrain dietary interpretations, owing to the good preservation and sulphur content of hair. It appears that analysis of the often-overlooked hair in archaeological sites may represent a significant new approach for u nderstanding ancient human communities.