Human-like external function of the foot, and fully upright gait, confirmed in the 3.66 million year old Laetoli hominin footprints by topographic statistics, experimental footprint-formation and computer simulation

Abstract

It is commonly held that the major functional features of the human foot (e.g. a functional longitudinal medial arch, lateral to medial force transfer and hallucal (big-toe) push-off ) appear only in the last 2 Myr, but functional interpretations of footbones and footprints of early human ancestors (hominins) prior to 2 million years ago (Mya) remain contradictory. Pixel-wise topographical statistical analysis of Laetoli footprint morphology, compared with results from experimental studies of footprint formation; foot-pressure measurements in bipedalism of humans and non-human great apes; and computer simulation techniques, indicate that most of these functional features were already present, albeit less strongly expressed than in ourselves, in the maker of the Laetoli G-1 footprint trail, 3.66 Mya. This finding provides strong support to those previous studies which have interpreted the G-1 prints as generally modern in aspect.

Laetoli footprints reveal bipedal gait biomechanics different from those of modern humans and chimpanzees

“…A second study showed that the shapes of the Laetoli footprints were significantly different from those of footprints created by humans walking with a strongly BHBK gait [14]. Both of these studies based their interpretations of the Laetoli tracks on the observation that the BHBK footprints in their simulations and experiments were relatively deep under the forefoot and shallow under the heel [14,15]. Here, we directly studied experimentally produced chimpanzee footprints and found that this pattern does not hold.…”

“…One analysis used forward dynamics computer simulations based on human muscle activity data to generate hypothetical pressure distributions beneath a lower limb and foot modelled based on skeletal dimensions of A. afarensis [15]. Based on dissimilarities between these hypothetical pressure distributions and the topography of the Laetoli footprints, the authors concluded that a BHBK gait could not have created the Laetoli prints.…”

“…Yet the conclusions of this study are limited by the small sample sizes. One study [15] compared plantar pressure records from non-human apes with the Laetoli footprints, although it has since been demonstrated by those same researchers [18] and others [19,20] that pressure distributions are only weakly related to footprint shapes, calling into question the extent to which non-human ape pressure distributions may reflect their footprint topographies. Even more important than the absence of relevant comparative footprint samples though has been the limited knowledge of how specific biomechanical variables are expressed in, and can be inferred from, footprint morphologies.…”

Human and avian running on uneven ground: a model-based comparison

“…Avian bipedalism traces back 230 million years to their dinosaur ancestors [1,2], whereas hominins have a significantly shorter bipedal history of at least 3.6 million years [3,4]. Although both humans and birds move bipedally, there are a number of morphological disparities, which will affect their locomotion.…”

A Medical Hypothesis: Excessive Adaptation Results in Relative Hypothermia and Lymphocytopenia, as Seen in Carnivorous Aquatic Mammals

“…Thus, animals with low body temperatures may have undergone greater adaptations, or more adaptation events, than those with higher body temperatures. Early human ancestors began bipedal walking 3.66 million years ago [14], likely because bipedal walking requires 75% less energy than quadrupedal walking [15]. Bipedal walking became the defining feature of the earliest hominids, and undoubtedly represented a drastic lifestyle change through adaptation; therefore, the low body temperature of humans might be due to our adaptation to bipedal locomotion.…”