Hip extensor mechanics and the evolution of walking and climbing capabilities in humans, apes, and fossil hominins

The evolutionary emergence of humans’ remarkably economical walking gait remains a focus of research and debate, but experimentally validated approaches linking locomotor capability to postcranial anatomy are limited. In this study, we integrated 3D morphometrics of hominoid pelvic shape with experimental measurements of hip kinematics and kinetics during walking and climbing, hamstring activity, and passive range of hip extension in humans, apes, and other primates to assess arboreal–terrestrial trade-offs in ischium morphology among living taxa. We show that hamstring-powered hip extension during habitual walking and climbing in living apes and humans is strongly predicted, and likely constrained, by the relative length and orientation of the ischium. Ape pelves permit greater extensor moments at the hip, enhancing climbing capability, but limit their range of hip extension, resulting in a crouched gait. Human pelves reduce hip extensor moments but permit a greater degree of hip extension, which greatly improves walking economy (i.e., distance traveled/energy consumed). Applying these results to fossil pelves suggests that early hominins differed from both humans and extant apes in having an economical walking gait without sacrificing climbing capability. Ardipithecus was capable of nearly human-like hip extension during bipedal walking, but retained the capacity for powerful, ape-like hip extension during vertical climbing. Hip extension capability was essentially human-like in Australopithecus afarensis and Australopithecus africanus, suggesting an economical walking gait but reduced mechanical advantage for powered hip extension during climbing

Evidence for Type Ia Supernova Diversity from Ultraviolet Observations with the Hubble Space Telescope

We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This dataset provides unique spectral time series down to 2000 Angstrom. Significant diversity is seen in the near maximum-light spectra (~ 2000--3500 Angstrom) for this small sample. The corresponding photometric data, together with archival data from Swift Ultraviolet/Optical Telescope observations, provide further evidence of increased dispersion in the UV emission with respect to the optical. The peak luminosities measured in uvw1/F250W are found to correlate with the B-band light-curve shape parameter dm15(B), but with much larger scatter relative to the correlation in the broad-band B band (e.g., ~0.4 mag versus ~0.2 mag for those with 0.8 < dm15 < 1.7 mag). SN 2004dt is found as an outlier of this correlation (at > 3 sigma), being brighter than normal SNe Ia such as SN 2005cf by ~0.9 mag and ~2.0 mag in the uvw1/F250W and uvm2/F220W filters, respectively. We show that different progenitor metallicity or line-expansion velocities alone cannot explain such a large discrepancy. Viewing-angle effects, such as due to an asymmetric explosion, may have a significant influence on the flux emitted in the UV region. Detailed modeling is needed to disentangle and quantify the above effects.Comment: 17 pages, 13 figures, accepted by Ap

Climbing Performance and Ecology in Humans, Chimpanzees, and Gorillas

This dissertation aims to establish the effects of limb proportions and body size on the climbing performance of humans, chimpanzees, and gorillas by assessing three aspects of climbing performance: 1) energetic cost, 2) fatigue, and 3) canopy access. Whether hominins were arboreal, and to what extent, is a matter of hot debate. Specifically, the relative prominence of vertical climbing in the locomotor repertoires of various hominin taxa remains a contested issue. Over the course of human evolution, both the body size and relative hindlimb length of hominins has increased. These traits are often linked to bipedality. Long forelimbs, in contrast, are hypothesized to be advantageous in vertical climbing. Apart from these statements, we know little about how size and body proportions specifically affect climbing performance. In the first study, I evaluated factors influencing the metabolic cost of locomotion (COLnet) during climbing. I assessed the effects of speed, route difficulty, experience, and anatomical variation of COLnet in rock climbers. Further, I compared the COLnet for these human climbers to that of non-human primates. I found that: 1) climbing speed is a significant predictor of climbing COLnet; 2) route difficulty is not significantly correlated to locomotor costs when controlling for speed; and 3) mass-specific locomotor costs are independent of body mass and limb proportions, both within and across species. From these results I concluded that neither changes in body mass nor limb proportions during hominin evolution are likely to have led to changes on the energetic aspect of climbing performance. In the second study, I examined the relationship between morphology, climbing grip strength (maximum voluntary contraction, MVC, of the finger flexors) and endurance (time one can maintain a grip strength greater or equal to 70% MVC) in human climbers. I showed that grip strength is negatively allometric to the function of body mass in rock climbers. Next, I tested whether strength limits tree climbing during foraging in Mbendjele foragers from the Republic of Congo. Mbendjele men’s grip strength did not significantly decrease after tree climbing. These results indicated that human foragers can accrue daily tree-climbing rates comparable to other African apes without approaching their limits of finger flexor strength or endurance. Finally, I tested whether and how humans and other apes differ in arboreal ecology, by collecting a comparative data set of positional behavior in trees of humans and sympatric chimpanzees and gorillas in northern Republic of Congo. I found that larger apes move more vertically within the core of trees and less horizontally into the periphery than smaller-bodied apes. However, despite their comparatively smaller body size, Mbendjele men spend significantly more time in the core than in the periphery of trees. In addition, humans spend significantly more time standing in trees bipedally than apes do. These results suggest that humans use trees differently than apes but are nonetheless adept in an arboreal environment and capable of foraging in the canopy. In this dissertation I combined the first investigation of sympatric human foragers and wild apes’ locomotor behavior with experimental laboratory studies. I detected no effect of limb proportions on energetic cost, fatigue, or canopy access. This suggests that fossil hominin and hominoids may have been less restricted in their locomotor repertoires than previous reconstructions predicted. I further show that modern humans are adept climbers, using a range of behaviors which allow them to access the canopy as effectively as chimpanzees and gorillas, despite humans’ anatomical specializations for terrestrial bipedalism

Scapular morphology of great apes and humans: A three-dimensional computed tomography-based comparative study

The primate scapula has been studied widely since its shape has been shown to correlate with how the forelimb is used in daily activities. In this study, we expand on the existing literature and use an image-based methodology that was originally developed for orthopaedic practice to quantify and compare the three-dimensional (3D) morphology of the scapula across humans and great apes. We expect that this image-based approach will allow us to identify differences between great apes and humans that can be related to differences in mobility and loading regime of the shoulder. We hypothesize that gorillas and chimpanzees will have a similar scapular morphology, geared towards stability and weight-bearing in knuckle-walking, whilst the scapular morphology of orangutans is expected to be more similar to that of humans given their high glenohumeral mobility associated with their suspensory lifestyle. We made 3D reconstructions of computed tomography scans of 69 scapulae from four hominid genera (Pongo, Gorilla, Pan and Homo). On these 3D bone meshes, the inferior glenoid plane was determined, and subsequently, a set of bony landmarks on the scapular body, coracoid, and acromion were defined. These landmarks allowed us to measure a set of functionally relevant angles which represent acromial overhang, subacromial space and coracoacromial space. The angles that were measured are: the delto-fulcral triangle (DFT), comprising the alpha, beta, and delta angle, the acromion-glenoid angle (AGA), the coracoid-glenoid centre-posterior acromial angle (CGA), the anterior tilt (TA CGA) and the posterior tilt of the CGA (PT CGA). Three observers placed the landmarks on the 3D bone meshes, allowing us to calculate the inter-observer error. The main differences in the DFT were found between humans and the great apes, with small differences between the great apes. The DFT of humans was significantly lower compared to that of the great apes, with the smallest alpha (32.7 degrees), smallest delta (45.7 degrees) and highest beta angle (101.6 degrees) of all genera. The DFT of chimpanzees was significantly higher compared to that of humans (p < 0.01), with a larger alpha (37.6 degrees) and delta angle (54.5 degrees) and smaller beta angle (87.9 degrees). The mean AGA of humans (59.1 degrees) was significantly smaller (p < 0.001) than that of gorillas (68.8 degrees). The mean CGA of humans (110.1 degrees) was significantly higher (p < 0.001) than in orangutans (92.9 degrees). Humans and gorillas showed mainly a posterior tilt of their coracoacromial complex whilst chimpanzees showed mainly an anterior tilt. The coracoacromial complex of the orangutans was not tilted anteriorly or posteriorly. With our image-based method, we were able to identify morphological features of the scapula that differed significantly between hominid genera. However, we did not find an overall dichotomy in scapular morphology geared towards high stability (Pan/Gorilla) or high mobility (Homo/Pongo). Further research is needed to investigate the functional implications of these differences in scapular morphology

Development of a cell transducible RhoA inhibitor TAT-C3 transferase and its encapsulation in biocompatible microspheres to promote survival and enhance regeneration of severed neurons

10.1007/s11095-007-9454-6Pharmaceutical Research24122297-230