THE EFFECT OF SOCIAL AND ENVIRONMENTAL STRESSES AMONG THE HISTORIC ARIKARA NATIVE AMERICANS

The Arikara Native Americans from the Anton Rygh, Mobridge, Larson and Leavenworth sites, inhabited the Great Plains of western North America (AD 1600-1832). The Arikara experienced climatic changes, warfare, interactions with novel groups of people and disease epidemics and therefore represent an opportunity to assess differential risk of death in a stressful context. The overarching question of this project is, in the historic context of environmental and social stresses, do these environmental and social stresses (as indicated by specific skeletal markers that occur during childhood) increase the risk of death from later infectious disease or warfare related trauma experienced in adulthood?

Risk of death was calculated using the semiparametric Kaplan-Meir survivorship curves with log-rank tests and the Cox proportional hazard model calculated in SPSS. Risk of death from specific, competing causes of death was further estimated using the parametric Gompertz and Gompertz-Makeham analyses in R. The Gompertz model assesses risk of death from adult mortality and the increase in mortality with age. The Gompertz-Makeham further assesses risk of death from random causes of death that are not age related. A total of 374 individuals, 192 males and 182 females, were included in these analyses. While none of the statistical results were statistically significant, they did reveal age- and sex- specific patterns of survivorship. Two main conclusions can be considered: First, females with a skeletal stress marker exhibit greater survivorship, particularly after age 40, whereas frail males exhibit a decrease in survivorship. Second, males and females with a skeletal stress marker exhibit decreased survivorship if they also exhibit a skeletal trauma. This decrease in survivorship may be due to dangerous social behaviors, such as warfare, hunting, horticultural activities or trade. Overall, these results indicate that mortality is indeed selective with respect to age, sex and/or stress status. Future research will address risk of death from individual health conditions as well as from multiple stress markers.