in unhealed metal blade injuries to the bones. Living or freshly dead bones are somewhat resilient, so metal blade injuries to bone will generate a linear cut with relatively clean edges rather than irregular shattering. Archaeologists have tried using the microscopic parallel scratch marks on cut bones in order to estimate the trajectory of the blade that caused the injury. Diet and dental health Caries Dental caries, commonly referred to as cavities or tooth decay, are caused by localized destruction of tooth enamel, as a result of acids produced by bacteria feeding upon and fermenting carbohydrates in the mouth. Subsistence based upon agriculture is strongly associated with a higher rate of caries than subsistence based upon foraging, because of the higher levels of carbohydrates in diets based upon agriculture. For example, bioarchaeologists have used caries in skeletons to correlate a diet of rice and agriculture with the disease. Females may be more vulnerable to caries compared to men, due to lower saliva flow than males, the positive correlation of estrogens with increased caries rates, and because of physiological changes associated with pregnancy, such as suppression of the immune system and a possible concomitant decrease in antimicrobial activity in the oral cavity. Stable isotope analysis Overview Stable isotope biogeochemistry is a powerful tool that utilizes variations in isotopic signatures and relates them to biogeochemical processes. The science is based on the preferential fractionation of lighter or heavier isotopes, which results in enriched and depleted isotopic signatures compared to a standard value. Essential elements for life such as carbon, nitrogen, oxygen, and sulfur are the primary stable isotope systems used to interrogate archeological discoveries. Isotopic signatures from multiple systems are typically used in tandem to create a comprehensive understanding of the analyzed material. These systems are most commonly used to trace the geographic origin of archaeological remains and investigate the paleodiets, mobility, and cultural practices of ancient humans. Over the past few decades the use of isotope geochemistry in the context of archaeology has dramatically increased. System Applications Carbon Stable isotope analysis of carbon in human bone collagen allows bioarchaeologists to carry out dietary reconstruction and to make nutritional inferences. These chemical signatures reflect long-term dietary patterns, rather than a single meal or feast. Isotope ratios in food, especially plant food, are directly and predictably reflected in bone chemistry, allowing researchers to partially reconstruct recent diet using stable isotopes as tracers. Stable