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The scientific examination of isotopes was traditionally a research cornerstone in physics, biochemistry and geology and only relatively recently been associated with the fields of archeology and anthropology. Atoms of elements, such as carbon or nitrogen, can assume different physical forms called isotopes, in which the number of protons in the atoms nucleus is the same but the number of neutrons varies, resulting in slightly different atomic weights between each isotope. According to Hoefs (1997), isotopes are divided into two fundamental groups, those that are stable and those that are radioactive or unstable. Presently, about 300 stable isotopes are known to exist, unstable isotopes on the other hand number more than 1200.

Isotope values can be measured in the tissues of all plants and animals. They are passed along the food chain from plants to animals, and therefore from our food into our body. The isotope values in human body tissues reflect to a large extent a mixture of all of the isotope values of all of the food eaten and fluid drunk. Because different types of foods have distinctive isotope signatures, measurements of the isotopic values of human bone allow assumptions to be made about the foods eaten by that individual. This type of analysis has the potential to provide fundamental dietary information such as the sorts of plants consumed, degree of carnivory, and helps in establishing the trophic level position of the individual being analyzed in the overall food chain.

Stable isotope studies of palaeodiet are based on the observation that the stable carbon and nitrogen isotopes of an organism appear to be maintained in its bone following death (DeNiro & Epstein 1978a, 1981), and that the stable isotopes of carbon and nitrogen in bone collagen from osteological remains provide direct information on the lifetime diets of past populations (Vogel & van der Merwe 1977). The earliest mention of the potential use of isotopes for dietary reconstruction appears in an unpublished report by Robert Hall in 1967 titled “More About Corn, Cahokia and Carbon-14”. Initial applications of stable isotope analysis to human dietary research utilized stable carbon isotopes and focused on the timing of the introduction of maize agriculture to various regions throughout North America. These examinations included the analysis of isotopic compositions of human bones from archaeological sites in Ohio, Illinois, New York, and West Virginia that revealed a gradual shift in diet from the Late Archaic period (around 2000 BC) to the Upper Mississippian period (around 1300 AD). This method has been widely applied in archaeology and physical anthropology since its introduction in 1977 in Europe, North America and South Africa. Extensive reviews of stable

isotope palaeodietary research have been presented by (Hare & Estep 1983, Haynes 1968, Koch 1998, Dorozynski & Anderson 1991, Katzenberg 1992, Keegan & DeNiro 1988, Ambrose 1987, 1993, DeNiro 1987, Norr 1995, Schoeninger & Moore 1992, Pate 1994, Schwarcz & Schoeninger 1991, Grupe 1987, van der Merwe 1982). Similar analysis also focused on the individual's diet over a lifetime (Renfrew & Bahn 1996) and others indicate that stable isotope analysis of carbon and nitrogen from collagen in human bone can also be utilized to determine what the relative proportions were of various foods present in the diet (Chisolm 1989). This method along with other indirect measures of human diet such as archeological artifacts, and faunal, botanical and skeletal analysis provides a much clearer picture of subsistence practices than previously possible.

Since the incorporation of stable isotope analysis in the arsenal of tools for clarifying questions in the archaeological context, a mass of experimental field studies far too vast to list in its entirety have documented the strong correlation between stable isotope ratios of nitrogen 15_N/14_{N, carbon} 13_C/12_{C and sulfur} 34_S/32_{S in vertebrates and that of their diets}

including (e.g. Bocherens et al. 2001, Richards et. al. 2000, 1998, Pingitore 2000, Richards & Hedges 1999a, 1999b, Richards 1996, Baraybar 1999, 1997, Grupe 1998, 1987, White 1998, McGovern & Quinn 1996, Sillen et al. 1998, Ambrose et. al. 1997, Cox & Sealy 1997, Mays 1997, Sillen & Lee-Thorp 1994, Ambrose & Norr 1993, Tieszen & Fagre 1993, Matson & Chisholm 1991, Ambrose 1991, 1987, 1986, Lee-Thorp et al. 1989a, 1989b, Schwarcz et al. 1985, Bender et al. 1981, Norr 1981). Other studies have shown that the ratio of 13C to 12C can be used to provide dietary information about extinct fauna (Lee-Thorp et al. 1994). The importance of isotopic investigations for hominid evolution was indicated by the analysis of

Australopithecus africanus by Sponheimer and Lee-Thorp (1999a), who found that early hominids ate not only fruits and leaves but also large quantities of 13C enriched foods such as grasses and sedges or animals that ate these plants, or both. The results suggest that early hominids regularly moved in open environments such as woodlands and grasslands for food. Lillie & Richards (2000) identifying subsistence strategies in Stone Age man by utilizing stable isotope analysis, and determined a fisher-hunter-gatherer diet of Mesolithic-Neolithic transition in the Ukraine. These and other studies like Ambrose and DeNiro (1989) also point out the important role environmental influences play in determining isotope compositions. The great advantage of stable isotope analysis is that it gives a direct measure of long term human diets on the individual level, whereas more traditional methods of diet reconstruction from environmental archaeology, such as floral and faunal analyses, give information about specific foods eaten, and may only reflect single or special meals. The majority of dietary

remnants originating from archaeological sites also tend to overemphasize faunal remains, particularly those with better taphonomic survivability, for example, long bone fragments from large mammals versus fish and bird skeletal elements. Palaeobotanical remains, or indicators for their presence such as phytolith assemblages (Eichhorn 2006), are only rarely preserved, sometimes being recovered from ceramic vessels, in the form of seeds or pollen in textiles or in graves that have survived the ages, or occasionally in the digestive tract of mummified humans. Other forms of dietary analysis involved the interpretation of skeletal pathologies (Marin et al. 1985) or dental microwear characteristics (Fine & Craig 1981). These too have their drawbacks, because they may simply be indicators of diet preferences over a brief time span.

There remains, however, a definite parallel between the interests of stable isotope researchers and those exploring past human diets by different means. Together with novel advances in technology and analytical methods, stable-isotope biochemistry is now frequently employed as a routine procedure at many institutions and progressively becoming an integral part of research investigations within the anthropological field. Presently, stable isotope ratios are even accessible online, allowing for quick and easy comparisons, an option facilitating the rapid, simple and efficient exchange of information so vital to any science (see OIPC, section 7.7).