Footprint evidence of early hominin locomotor diversity at Laetoli, Tanzania.

Bipedal trackways discovered in 1978 at Laetoli site G, Tanzania and dated to 3.66 million years ago are widely accepted as the oldest unequivocal evidence of obligate bipedalism in the human lineage1-3. Another trackway discovered two years earlier at nearby site A was partially excavated and attributed to a hominin, but curious affinities with bears (ursids) marginalized its importance to the paleoanthropological community, and the location of these footprints fell into obscurity3-5. In 2019, we located, excavated and cleaned the site A trackway, producing a digital archive using 3D photogrammetry and laser scanning. Here we compare the footprints at this site with those of American black bears, chimpanzees and humans, and we show that they resemble those of hominins more than ursids. In fact, the narrow step width corroborates the original interpretation of a small, cross-stepping bipedal hominin. However, the inferred foot proportions, gait parameters and 3D morphologies of footprints at site A are readily distinguished from those at site G, indicating that a minimum of two hominin taxa with different feet and gaits coexisted at Laetoli.

Kinetics of stone tool production among novice and expert tool makers.

OBJECTIVES: As is the case among many complex motor tasks that require prolonged practice before achieving expertise, aspects of the biomechanics of knapping vary according to the relative experience/skill level of the practitioner. In archaeological experiments focused on the production of Plio-Pleistocene stone tools, these skill-mediated biomechanical differences have bearings on experimental design, the interpretation of results, and lithic assemblage analysis. A robust body of work exists on variation in kinematic patterns across skill levels but less is known about potential kinetic differences. The current study was undertaken to better understand kinetic patterns observed across skill levels during "Oldowan," freehand stone tool production. MATERIALS AND METHODS: Manual pressure data were collected from 23 novice and 9 expert stone tool makers during the production of simple stone flakes using direct hard hammer percussion. RESULTS: Results show that expert tool makers experienced significantly lower cumulative pressure magnitudes and pressure-time integral magnitudes compared with novices. In expert knappers, digits I and II experienced similarly high pressures (both peak pressure and pressure-time integrals) and low variability in pressure relative to digits III-V. Novices, in contrast, tended to hold hammerstones such that pressure patterns were similar across digits II-V, and they showed low variability on digit I only. DISCUSSION: The similar and consistent emphasis of the thumb by both skill groups indicates the importance of this digit in stabilizing the hammerstone. The emphasis placed on digit II is exclusive to expert knappers, and so this digit may offer osteological signals diagnostic of habitual expert tool production.

The manual pressures of stone tool behaviors and their implications for the evolution of the human hand.

It is widely agreed that biomechanical stresses imposed by stone tool behaviors influenced the evolution of the human hand. Though archaeological evidence suggests that early hominins participated in a variety of tool behaviors, it is unlikely that all behaviors equally influenced modern human hand anatomy. It is more probable that a behavior's likelihood of exerting a selective pressure was a weighted function of the magnitude of stresses associated with that behavior, the benefits received from it, and the amount of time spent performing it. Based on this premise, we focused on the first part of that equation and evaluated magnitudes of stresses associated with stone tool behaviors thought to have been commonly practiced by early hominins, to determine which placed the greatest loads on the digits. Manual pressure data were gathered from 39 human subjects using a Novel Pliance® manual pressure system while they participated in multiple Plio-Pleistocene tool behaviors: nut-cracking, marrow acquisition with a hammerstone, flake production with a hammerstone, and handaxe and flake use. Manual pressure distributions varied significantly according to behavior, though there was a tendency for regions of the hand subject to the lowest pressures (e.g., proximal phalanges) to be affected less by behavior type. Hammerstone use during marrow acquisition and flake production consistently placed the greatest loads on the digits collectively, on each digit and on each phalanx. Our results suggest that, based solely on the magnitudes of stresses, hammerstone use during marrow acquisition and flake production are the most likely of the assessed behaviors to have influenced the anatomical and functional evolution of the human hand.

Participation, representation, and shared experiences of women scholars in biological anthropology.

American Association of Physical Anthropologists (AAPA) membership surveys from 1996 and 1998 revealed significant gender disparities in academic status. A 2014 follow-up survey showed that gender equality had improved, particularly with respect to the number of women in tenure-stream positions. However, although women comprised 70% of AAPA membership at that time, the percentage of women full professors remained low. Here, we continue to consider the status of women in biological anthropology by examining the representation of women through a quantitative analysis of their participation in annual meetings of the AAPA during the past 20 years. We also review the programmatic goals of the AAPA Committee on Diversity Women's Initiative (COD-WIN) and provide survey results of women who participated in COD-WIN professional development workshops. Finally, we examine the diversity of women's career paths through the personal narratives of 14 women biological anthropologists spanning all ranks from graduate student to Professor Emeritus. We find that over the past 20 years, the percentage of women first authors of invited symposia talks has increased, particularly in the sub-disciplines of bioarchaeology, genetics, and paleoanthropology. The percentage of women first authors on contributed talks and posters has also increased. However, these observed increases are still lower than expected given the percentage of graduate student women and women at the rank of assistant and associate professor. The personal narratives highlight first-hand the impact of mentoring on career trajectory, the challenges of achieving work-life satisfaction, and resilience in the face of the unexpected. We end with some suggestions for how to continue to improve equality and equity for women in biological anthropology.