Center for the Advanced Study of Hominin Paleobiology, George Washington University
March 27, 2015 , Archview Ballroom
Humans are the only mammals known to move resources across substantial distances. This behavior, which combines habitual bipedalism with use of the arms or head for carrying, has been linked with the emergence of two aspects of modern social dynamics: alloparenting and non-infant provisioning. Unfortunately, most paleontological and archaeological evidence of carrying is indirect, and its role in hominin evolution is difficult to test. However, fossil footprints directly record aspects of locomotion, such as foot pressure distribution, representing an opportunity to identify evidence of carrying behavior in the fossil record. This study tests the hypothesis that carrying objects produces unique plantar pressure patterns.
We asked 20 habitually unshod or minimally shod Daasanach adults to walk across a pressure pad while carrying sandbags weighing 20% of their body weight in each of three configurations (at chest, shoulder, and head), and a control condition without weight. Pressure values were normalized relative to peak and an ANOVA was performed to test for differences under 1) corresponding metatarsal heads of the left and right feet; 2) each metatarsal head of the control condition, and the corresponding zones of the same foot in carrying conditions. In each condition, plantar pressure distribution under left and right feet were distinct from one another, with the fewest differences observed when head carrying. Furthermore, shoulder carrying produced the greatest differences in pressure distribution from the control under metatarsals 1, 2, and 5. We hypothesize that carrying may similarly affect external foot motions and may be recognizable in fossil footprints.
Funded by the National Science Foundation (Graduate Research Fellowship GRFP-2013169744, IGERT DGE-0801634, BCS-1128170), GW Centers and Institute Facilitating Fund.