For much of the Pliocene and Pleistocene, multiple hominin species coexisted in the same regions of eastern and southern Africa. Due to the limitations of the skeletal fossil record, questions regarding their interspecific interactions remain unanswered. We report the discovery of footprints (~1.5 million years old) from Koobi Fora, Kenya, that provide the first evidence of two different patterns of Pleistocene hominin bipedalism appearing on the same footprint surface. New analyses show that this is observed repeatedly across multiple contemporaneous sites in the eastern Turkana Basin. These data indicate a sympatric relationship between Homo erectus and Paranthropus boisei , suggesting that lake margin habitats were important to both species and highlighting the possible influence of varying levels of coexistence, competition, and niche partitioning in human evolution.

The modern human hand is an intriguing mix of primitive morphology and derived function. Traditionally, its form and function are explained as a functional "trade-off" between the requirements of locomotion and manipulation, but recently acquired comparative, experimental and fossil evidence suggests that this functional trade-off is more complex than conventional wisdom suggests. Moreover, when studying hand evolution within the hominin clade, the only morphological evidence comes from the hard-tissues, and evidence about hand function must be inferred indirectly from the archaeological record. We lack information about critical aspects of hand form (e.g., soft tissues) and function (e.g., neurology) as well as non-lithic evidence about behavior. Thus, comparative anatomical, experimental and ethological studies of modern humans and other primates are critical to making more informed inferences about hand use in the past. We review the relevant fossil and archaeological evidence within the relevant comparative context (e.g., other extant apes and dexterous monkeys) in an attempt to reconstruct hand evolution within the hominin clade. We conclude by summarizing our current understanding-or lack thereof-of the evolutionary history of the modern human hand.

The production of Oldowan tools has long been assumed to represent a significant cognitive shift in early hominins. Such a shift in cognition has been proposed as key to understanding other important behavioral changes in diet, land use, and social structure, as well as the emergence of our genus, Homo. Many studies have examined the knowledge and skills required of Oldowan tool-makers to ascertain what, if anything, about this task in particular may have presented a unique, cognitive challenge. Here, we approach this topic from a mechanical perspective, asking how the production of simple flake tools differs from nut-cracking, as well as other evolutionarily relevant, forelimb-dominated actions. We propose that the mechanical requirements of flake removal are not particularly challenging relative to nut-cracking in capuchins, the species for whom the most relevant comparative data exists. Similarly, while speed-accuracy tradeoffs during knapping could represent an additional challenge relative to nut-cracking, these parameters are actually dealt in discrete ways that simplify the motor control challenges of the task overall. Given these findings, we suggest future research into hominin brain evolution at this time of focus on other nonbiomechanical aspects of tool production/use or nontool-related demands going forward.

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 lineage 1 – 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 obscurity 3 – 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.

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.

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.

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.

Relative to the hominin fossil record there is an abundance of lithic artefacts within Pleistocene sequences. Therefore, stone tools offer an important source of information regarding hominin behaviour and evolution. Here we report on the potential of Oldowan and Acheulean flake artefacts to provide a record of the biomechanical demands placed on the hominin hand during Lower Palaeolithic stone tool production sequences. Specifically, we examine whether the morphometric attributes of stone flakes, removed via hard hammer percussion, preserve correlates of the pressures experienced across the dominant hand of knappers. Results show that although significant and positive relationships exist between flake metrics and manual pressure, these relationships vary significantly between subjects. Indeed, we identify two biomechanically distinct strategies employed by knappers; those that alter their hammerstone grip pressure in relation to flake size and mass and those who consistently exert relatively high manual pressures. All individuals experience relatively high gripping pressure when detaching particularly large flakes. Amongst other results, our data indicate that the distinctive large flake technology associated with the Acheulean techno-complex may be demonstrative of an ability to withstand, and by extension, to exert higher manual pressures. However inferences from smaller flake artefacts, especially, must be treated with caution due to the variable biomechanical strategies employed.

Humans are unique among extant primates in possessing a true flexor pollicis longus (FPL) muscle thought to be a key component to the evolution of human dexterity and tool making. In most non‐human primates, it is either not present or part of the flexor digitorum profundus muscle, with a tendon attaching to the first digit. Recently, researchers have noticed further variation of this unique forearm muscle in humans, specifically the presence of an accessory muscle belly. Some have documented a prevalence of up to 50% of this accessory head (AHFPL) in cadavers, and many have debated its clinical function. The goal of this study was to further assess the prevalence of this muscle belly. If present, we determined its origin, attachment, innervation and blood supply. Finally, we measured aspects of muscle architecture and mechanics, including muscle belly, tendon, and fiber lengths, muscle mass, pennation angle, and physiological cross‐sectional area (PCSA), in hopes to shed light on the functionality of this accessory head.We collected data from 80 cadavers between 23 and 98 years of age from Midwestern University. The pool prevalence of an AHFPL was 67.5% (n = 54). Contrary to past studies where AHFPL was found more commonly in men than in women, we found that 63% of the AHFPL occurrence was found in women. We also found that 72% of the cadavers had a bilateral presence of AHFPL. When present unilaterally, the left side was 50% more prevalent than the right. AHFPL has been documented to take origin proximally and medially to the FPL muscle belly, more specifically from the medial epicondyle of the humerus. However, we found that 93% of the time AHFPL actually took origin on the common flexor tendon and only reached the medial epicondyle 3% of the time. As in previous studies, we found that AHFPL inserted more often on the tendon or the muscle belly of FPL. However the location where the accessory head inserted on FPL was extremely variable (24.26 to 233.97 mm from the origin of FPL). This greatly changed the orientation, size, and shape of AHFPL. In most cases AHFPL was innervated by the anterior interosseous nerve (74%) and supplied by the artery of the same name (65%).After analyzing the muscle architectural data, we found that men had significantly longer fiber and tendon lengths as well as greater muscle mass and PCSA than women. In general though, the take home message from the functional data was variability. For example, the AHFPL ranged in weight from 0.3 to 3.05 g and in muscle belly length from 47.03 to 154.23 mm. All muscular architectural data had a huge range of variation, which was expressed as significantly in men as in women. We believe that the different insertion locations dictated the variability of the accessory head. Further analyses are needed to be able to determine the exact functionality of AHFPL. However, the high prevalence of AHFPL should be considered as part of normal human anatomy, instead of an anatomical variant. Due to the significant variations in the size and shape of the muscle, reliable anatomical knowledge is crucial to accurately diagnose and treat potential nerve entrapment, especially the anterior interosseous nerve.Support or Funding InformationThis study was generously funded by the Kenneth A. Suarez CCOM Fellowship, Chatham University and Midwestern University.