Fluctuating asymmetry as a measure of developmental instability in Arikara bioarchaeological assemblages

Abstract

Fluctuating asymmetry (FA) has been advanced as a tool for investigating the developmental instability of human populations and has more recently found its way into bioarchaeological investigations. The research presented here seeks to build upon those investigations and determine whether specific measures of FA can provide meaningful insight into the developmental instability of past Arikara populations represented in archaeological variants of the Coalescent tradition. Specifically, cranial morphometric, cranial nonmetric, and post-cranial metric measurements have been used to determine if meaningful patterns in the magnitude of FA across variants of the Coalescent tradition can be detected. The data that form the basis of this research originate from skeletal assemblages excavated from numerous Arikara archaeological sites along the Missouri River in South Dakota. These assemblages were selected for this study because they represent a single, culturally and genetically affiliated population that can be examined over the course of several centuries during which time the Arikara experienced variability in environmental and social stressors--the suspected cause of developmental instability. Moreover, several of these skeletal assemblages provide rather large samples, which is ideal when assessing FA in order to avoid the possible influences of small samples such as sampling error. Three approaches to data collection and analysis are included in the study. Patterns of FA were assessed for nonmetric traits of the cranium and metric traits of the post-cranial skeleton. In addition, three-dimensional craniometric data were assessed for fluctuating asymmetry through the applications of Euclidean Distance Matrix Analysis (EDMA). A hypothesis for the relative ordering of the magnitude of FA was developed based on archaeological/ethnohistorical information regarding potential social stressors, prior studies that have examined the health of the Arikara, and information regarding the changing climatic conditions during the four variants of the Coalescent tradition. The hypothesized ordering of the magnitude of FA, from least to greatest, is: Post-Contact Coalescent, Extended Coalescent, Initial Coalescent, and Disorganized Coalescent. However, the results do not fully support this ordering. While the Disorganized Coalescent did display rather high magnitudes of fluctuating asymmetry in certain measures and dimensions, the Post-Contact Coalescent was found to represent some of the highest magnitudes of fluctuating asymmetry, especially for the craniometric measures. If fluctuating asymmetry is indeed a suitable measure of developmental instability, then the major implication of this study is that a reevaluation of the Coalescent variants may be in order. Specifically, the Post-Contact coalescent may not have been a period of fluorescence and prosperity for the Arikara as has been described elsewhere. Alternatively, it may be that these archaeological variants do not provide an appropriate chronological resolution for assessing fluctuating asymmetry within this population.