Dynamic similarity predicts gait parameters for Homo floresiensis and the Laetoli hominins

Late in 2004, the skeletal remains of a pygmy-sized hominin recovered from a cave on the Indonesian island of Flores were first documented, with the authors concluding that the "postcranial anatomy [was] consistent with human-like obligate bipedalism" (Brown et al. [2004]: Nature 431:1055-1061). We have assumed that Homo floresiensis, who was estimated to be 18,000-years-old, walked with a gait pattern that was dynamically similar to modern man. The dynamic similarity hypothesis was also applied to the Australopithecines that left their footprints at Laetoli 4-million-years ago. According to this hypothesis, dimensionless gait parameters can be used in combination with known leg length or step length to calculate velocity of bipedal locomotion. We have gathered data on 20 extant modern humans to calculate the standard estimates of error when predicting gait parameters. We predict that the Homo floresiensis specimen walked at a velocity of 1.11 +/- 0.14 m/s. For the Laetoli footprints, the velocity for Track 1 was estimated to be 1.03 +/- 0.12 m/s and for Track 2 to be 1.14 +/- 0.12 m/s. These latter values for Australopithecines are greater than prior analyses, but are in good agreement with more recent work based on evolutionary robotics. Since modern man walks at 1.44 +/- 0.14 m/s, our results suggest that, despite their diminutive size, these ancient hominins were capable of ranging across a wide geographical area.