Biomechanical insights into activity and long distance trade in the south-central Andes (AD 500–1450)

• Lower limb biomechanics were used to infer spatial/temporal trends in mobility.
• Robusticity at San Pedro de Atacama was lowest in the Middle Horizon (AD 500–1000).
• This suggests lower mobility and a role as trading hub at this time.
• Robusticity was then highest at the transition to the Late Intermediate Period.
• This suggests a more active role in trade as relations with Tiwanaku collapsed.

Long distance trade has been attributed important social and economic roles in the pre-colonial south-central Andes, but how these trade networks were operated and organised, and the roles played by different populations and social groups (e.g. elites), remain uncertain. This study aims to offer new perspective on these questions through biomechanical analyses of human skeletal remains from a probable key site in these networks, San Pedro de Atacama (SPdA). Groups that were more intensively involved in long distance trade are expected to have been more habitually mobile, and thus to show greater robusticity and less circular lower limb bone cross-sections. Lower limb biomechanical properties of elite and non-elite Middle Horizon groups (MH, AD 500–1000) were compared with subsequent transitional MH-Late Intermediate Period (LIP, AD 1000–1450) and LIP groups from SPdA, and with LIP groups from Pica-8 and the Azapa Valley. The results indicate that MH populations from SPdA had less robust lower limbs and were by inference less mobile than their successors, with no differences between elite and non-elite, while robusticity was elevated in the MH-LIP transition group. Alternative explanations for the results, such as changes in herding activities, cannot be entirely discounted based on current evidence, but the results are consistent with hypotheses that SPdA may have served as a hub on long distance trade networks during the MH, before residents became more actively involved in long distance trade following the collapse of key links with the Tiwanaku polity. The results also indicate similar levels of robusticity among LIP populations at SPdA, Pica-8 and in the Azapa Valley, implying they may have been involved in trading activities to a similar extent, and perhaps to a greater extent than SPdA MH groups, as regional intergroup relationships changed.