Temporal changes in limb proportionality among skeletal samples of Arikara Indians

Relative lengths of the radius, humerus, tibia and femur were examined in children obtained from ten archaeological sites in South Dakota. The sites range in time from about AD 1600 to 1830, and all are attributed to the Arikara Indians or their immediate ancestors. Changes in long bone proportions were examined by regressing the log of each bone on the log of the sum of all four bones. The regression coefficient which results represents the relative rate of change of the bone in relation to the sum of all bones. Proximal bones were found to increase faster than distal bones in both upper and lower limbs, and lower limbs increase faster than upper ones. The regression coefficients for tibia and femur exhibit significant heterogeneity over the ten sites, indicating that the pattern of proportional changes with growth is not the same for all groups. Furthermore, variation in regression coefficients among sites is temporally patterned, early sites being characterized by relatively longer femora and shorter tibiae, while the reverse is the case for the late sites. The temporal nature of relative femur-tibia lengths suggests that this is an adaptive change possibly with both genetic and nongenetic components.