Some theoretical aspects of isotope paleodiet studies

The introduction of stable isotope analysis (carbon, nitrogen, hydrogen, sulphur) of bones and food residues allows anthropologists to define more precisely the actual consumption patterns of extinct populations. However, this requires that: (a) we know the ranges of compositions of possible foods; (b) that there be isotopic variability in these foods (although some information about trophic-levels can be obtained for consumers of isotopically monotonous foods; (c) that isotopic offsets (fractionations) between diet and sample (e.g. collagen) are known; and (d) that samples are well-preserved. We can determine the dietary proportions of N + 1 foods if isotope ratios are measured for N elements and if no three foods are co-linear in δ-space. Studies of ancient human populations from North and Central America are used to show that: (a) variation in diet within a single time plane for a given “culture” is very limited except possibly where status differences occur; (b) variation in diet through space and time can be easily recognized and may in some cases be related to independently inferrable historical or environmental factors.