A Demographic Analysis of Skeletons from the Larson Site (39WW2), Walworth County, South Dakota

Paleodemographic analysis of 706 skeletons recovered from the Larson site (39WW2), Walworth County, South Dakota, is presented. The site was a protohistoric Arikara village and cemetery dating to approximately A. O. 1750-1781. Major objectives of this study were to reconstruct vital statistics of the Larson population and to determine population size of the village which contributed to the cemetery.

Analysis was accomplished using a life table methodology assuming a stationary population model. Vital statistics examined include data on mortality, survivorship, age-specific probability of death, life expectancy, and crude mortality rates. Interpopulation comparisons were made with other American Indian and world populations to determine differences unique to the Larson mortality profile. Causes of death are examined using available historical information and results from paleopathological analysis. Demographic data are applied to test a hypothesis that village abandonment was caused by a smallpox epidemic of 1780-1781. An attempt was made to identify areas of the cemetery which contain burials caused by this epidemic. Vital statistics reevaluated with elimination of these epidemic skeletal deposits allow assessment of the distortion in life table values produced by the inclusion of epidemic-related mortality.

Results indicate that the population had an extremely high infant mortality rate which remained fairly high throughout childhood. Adolescents enjoyed good health, having the lowest probability of death of all age categories. Mortality increased for young adults, ages 15-19, particularly for females. A second major mode in the female mortality curve is at ages 35-39. The greatest percentage of male deaths occurred in the fourth decade, especially ages 30-34. Only 1.9 percent of the population attained an age greater than 55 years.

Crude death rate of the Larson population equaled 70 per thousand per year. This estimate is in accord with archaeological and historical sources which report a rapid Arikara population decline during the Post-Contact period. Causes of death included, intertribal warfare, childbirth and obstetrical care, and disease, especially tuberculosis and smallpox.

Demographic data supports the hypothesis that the population was infected by smallpox and that error from the normal population vital statistics is caused by the inclusion of epidemic-produced mortality. However, the quantitative changes observed are not dramatic and indicate that large skeletal samples mask the appearance of brief fluctuations in mortality rates.

Larson village population size is estimated to have been between 430 and 560 people.