The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)

Earliest direct evidence of modern human-like foot function from 1.5 Ma hominin footprints at Ileret, Kenya


1Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, The George Washington University, 2Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, 3Division of Anthropology, American Museum of Natural History

March 27, 2015 2:00, Grand Ballroom E/F/G Add to calendar

The modern human foot generates propulsion during bipedal locomotion using a functional pattern that is unlike any other extant apes. Understanding when this functional pattern emerged during human evolution is complicated by the fact that soft tissues do not fossilize and complete, associated foot and leg skeletons are not known for any early hominins. However, fossil hominin footprints preserve direct records of the external motions of fossil hominin feet, and recent discoveries allow for a new approach to address this question.

Newly discovered 1.5 Ma fossil hominin footprints from Ileret, Kenya were compared to the footprints of habitually barefoot modern humans and the 3.7 Ma footprints from Laetoli, Tanzania. Resampling analyses were used for quantitative comparisons, and 3-D geometric morphometrics were used to visualize morphological differences. Differences were interpreted in the context of experimental results that link patterns of footprint variation to gait biomechanics. The Ileret footprints preserve forefoot morphologies similar to those of modern human footprints, while the Laetoli footprints differ significantly. The 1.5 Ma Ileret footprints therefore preserve the earliest direct evidence of human-like foot function, including a medial transfer of pressure and propulsion derived from the medial forefoot. We argue that this implies a human-like morphology of many, if not all, of the anatomical structures in the legs and feet of the hominins who created these footprints. These results support the hypothesis that an essentially modern human bipedal gait was not present at 3.7 Ma, but evolved in certain hominin taxa by the early Pleistocene.

We are grateful for funding support from the Leakey Foundation, the National Science Foundation (BCS-1232522, BCS-1128170, DGE-080163), the Wenner-Gren Foundation, and The George Washington University’s Centers and Institutes Facilitating Fund.