isotope analysis monitors the ratio of carbon 13 to carbon 12 (13C/12C), which is expressed as parts per mil (per thousand) using delta notation (δ13C). The 13C and 12C ratio is either depleted (more negative) or enriched (more positive) relative to an international standard. The original standard used in carbon stable isotope analysis is Pee Dee Belemnite (PDB), though this material has since been exhausted and replaced. 12C and 13C occur in a ratio of approximately 98.9 to 1.1. The ratio of carbon isotopes in consumers varies according to the types of plants digested with different photosynthesis pathways. The three photosynthesis pathways are C3 carbon fixation, C4 carbon fixation and Crassulacean acid metabolism. C4 plants are mainly grasses from tropical and subtropical regions, and are adapted to higher levels of radiation than C3 plants. Corn, millet and sugar cane are some well-known C4 domesticates, while all trees and shrubs use the C3 pathway. C4 carbon fixation is more efficient when temperatures are high and atmospheric CO2 concentrations are low. C3 plants are more common and numerous than C4 plants as C3 carbon fixation is more efficient in a wider range of temperatures and atmospheric CO2 concentrations. The different photosynthesis pathways used by C3 and C4 plants cause them to discriminate differently towards 13C leading to distinctly different ranges of δ13C. C4 plants range between -9 and -16‰, and C3 plants range between -22 to -34‰. The isotopic signature of consumer collagen is close the δ13C of dietary plants, while apatite , a mineral component of bones and teeth, has an ~14‰ offset from dietary plants due fractionation associated with mineral formation. Stable carbon isotopes have been used as tracers of C4 plants in paleodiets. For example, the rapid and dramatic increase in 13C in human collagen after the adoption of maize agriculture in North America documents the transition from a C3 to a C4 (native plants to corn) diet by 1300 CE. Skeletons excavated from the Coburn Street Burial Ground (1750 to 1827 CE) in Cape Town, South Africa, were analyzed using stable isotope data in order to determine geographical histories and life histories of the interred. The people buried in this cemetery were assumed to be slaves and members of the underclass based on the informal nature of the cemetery; biomechanical stress analysis and stable isotope analysis, combined with other archaeological data, seem to support this supposition. Based on