Stable isotopes of carbon and nitrogen as tracers for paleo-diet reconstruction

The isotopic compositions of the tissues of animals and humans are determined by the proportions of the various nutrients which they consume. This allows us to determine how much of each of their available foods were actually consumed over various parts of their lifetime. We apply this to ancient humans by analysis of bones, teeth and, rarely desiccated softer tissues (hair, skin). We review variations in δ¹³C and δ¹⁵N of known classes of nutrients (plants and animals), and discuss the chemical species whose isotopic composition can be analysed: collagen, bone-mineral, and lipids (cholesterol, etc.). Some variation in δ¹⁵N also arises from variations in δ¹⁵N of soil, particulate matter in the sea, and effect of aridity on N balance in terrestrial animals. Examples are presented of variation in δ¹³C due to consumption of maize (a C4 plant) and in d15N due to trophic level effects in prehistoric hunter-gatherers.