A paradigmatic account may suffice to explain behavioral evolution in early Homo. We propose a parsimonious account that (1) could explain a particular, frequently-encountered, archeological outcome of behavior in early Homo - namely, the fashioning of a Paleolithic stone \'handaxe\' - from a biological theoretic perspective informed by the free energy principle (FEP); and that (2) regards instances of the outcome as postdictive or retrodictive, circumstantial corroboration. Our proposal considers humankind evolving as a self-organizing biological ecosystem at a geological time-scale. We offer a narrative treatment of this self-organization in terms of the FEP. Specifically, we indicate how \'cognitive surprises\' could underwrite an evolving propensity in early Homo to express sporadic unorthodox or anomalous behavior. This co-evolutionary propensity has left us a legacy of Paleolithic artifacts that is reminiscent of a \'snakes and ladders\' board game of appearances, disappearances, and reappearances of particular archeological traces of Paleolithic behavior. When detected in the Early and Middle Pleistocene record, anthropologists and archeologists often imagine evidence of unusual or novel behavior in terms of early humankind ascending the rungs of a figurative phylogenetic \'ladder\' - as if these corresponded to progressive evolution of cognitive abilities that enabled incremental achievements of increasingly innovative technical prowess, culminating in the cognitive ascendancy of Homo sapiens. The conjecture overlooks a plausible likelihood that behavior by an individual who was atypical among her conspecifics could have been disregarded in a community of Hominina (for definition see Appendix 1) that failed to recognize, imagine, or articulate potential advantages of adopting hitherto unorthodox behavior. Such failure, as well as diverse fortuitous demographic accidents, would cause exceptional personal behavior to be ignored and hence unremembered. It could disappear by a pitfall, down a \'snake\', as it were, in the figurative evolutionary board game; thereby causing a discontinuity in the evolution of human behavior that presents like an evolutionary puzzle. The puzzle discomforts some paleoanthropologists trained in the natural and life sciences. They often dismiss it, explaining it away with such self-justifying conjectures as that, maybe, separate paleospecies of Homo differentially possessed different cognitive abilities, which, supposedly, could account for the presence or absence in the Pleistocene archeological record of traces of this or that behavioral outcome or skill. We argue that an alternative perspective - that inherits from the FEP and an individual\'s \'active inference\' about its surroundings and of its own responses - affords a prosaic, deflationary, and parsimonious way to account for appearances, disappearances, and reappearances of particular behavioral outcomes and skills of early humankind.

In 1987, Phillip Tobias published a comprehensive anatomical analysis of the endocasts attributed to Homo habilis, discussing issues dealing with brain size, sulcal patterns, and vascular traces. He suggested that the neuroanatomy of this species evidenced a clear change toward many cerebral traits associated with our genus, mostly when concerning the morphology of the frontal and parietal cortex. After more than 30 years, the fossil record associated with this taxon has not grown that much, but we have much more information on cranial and brain biology, and we are using a larger array of digital methods to investigate the paleoneurological variation observed in the human genus. Brain volume, the size of the frontal lobe, or the gross hemispheric asymmetries are still relevant issues, but they are considered to be less central than before. More attention is instead being paid to the cortical organization, the relationships with the cranial architecture, and the influence of molecular or ecological factors. Although the field of paleoneurology can currently count on a larger range of tools and principles, there is still a general lack of anatomical information on many endocranial traits. This aspect is probably crucial for the agenda of paleoneurology. More importantly, the whole science is undergoing a delicate change, because of the growing influence of the social environment. In this sense, the disciplines working with fossils (and, in particular, with brain evolution) should take particular care to maintain a healthy professional situation, avoiding an excess of speculation and overstatement.

The origins of Homo, as well as the diversity and biogeographic distribution of early Homo species, remain critical outstanding issues in paleoanthropology. Debates about the recognition of early Homo, first appearance dates, and taxonomic diversity within Homo are particularly important for determining the role that southern African taxa may have played in the origins of the genus. The correct identification of Homo remains also has implications for reconstructing phylogenetic relationships between species of Australopithecus and Paranthropus, and the links between early Homo species and Homo erectus. We use microcomputed tomography and landmark-free deformation-based three-dimensional geometric morphometrics to extract taxonomically informative data from the internal structure of postcanine teeth attributed to Early Pleistocene Homo in the southern African hominin-bearing sites of Sterkfontein, Swartkrans, Drimolen, and Kromdraai B. Our results indicate that, from our sample of 23 specimens, only 4 are unambiguously attributed to Homo, 3 of them coming from Swartkrans member 1 (SK 27, SK 847, and SKX 21204) and 1 from Sterkfontein (Sts 9). Three other specimens from Sterkfontein (StW 80 and 81, SE 1508, and StW 669) approximate the Homo condition in terms of overall enamel-dentine junction shape, but retain Australopithecus-like dental traits, and their generic status remains unclear. The other specimens, including SK 15, present a dominant australopith dental signature. In light of these results, previous dietary and ecological interpretations can be reevaluated, showing that the geochemical signal of one tooth from Kromdraai (KB 5223) and two from Swartkrans (SK 96 and SKX 268) is consistent with that of australopiths.

Five well-preserved individuals from Dmanisi represent a paleodeme attributed to early Homo. Here we provide a case study of the D2280 adult cranium, which presents four oval-shaped lesions on the frontal, left parietal, and occipital bones. Several conditions are considered as possibly contributing to this pathology, including trauma, cysts, metastatic cancer, and infectious disease. One large but shallow depression on the left parietal bone has slightly elevated boundaries. Imaging reveals inner and outer tables that are reciprocally concave, so that the diploë is diminished or completely absent. This lesion is very likely a result of traumatic injury. Two additional depressions on the left side frontal and occipital bones may also be attributed to blunt force trauma. Such injuries stem from a variety of causes, but interpersonal violence may well be implicated. Based on the location and structure of a fourth lesion on the right-side frontal bone, we advance a possible diagnosis of treponemal disease. Lesions on the cranium and specifically on the frontal bone are common in treponemal disease. The condition develops as a periostitis, which eventually results in the destruction of the osteoperiosteal border of the cranial outer table and rarely involves the inner table. Additional perforations on the occipital bone are interpreted as perimortem damage resulting from predation by carnivores or scavenging by birds. If our reading of this cranial evidence can be confirmed, then D2280 documents one of the earliest instances of blunt force trauma in the Homo lineage. Dmanisi may also reveal the presence of treponemal disease in a population dated ca. 1.77 Ma ago. These findings bear on the social behavior of ancient humans and also the impact of infectious diseases on their survival.

The Early Pleistocene site of Swartkrans in South Africa\'s Cradle of Humankind World Heritage Site has been significant for our understanding of the evolution of both early Homo and Paranthropus, as well as the earliest archaeology of southern Africa. Previous attempts to improve a faunal age estimate of the earliest deposit, Member 1, had produced results obtained with uranium-lead dating (U-Pb) on flowstones and cosmogenic burial dating of quartz, which placed the entire member in the range of >1.7/1.8 Ma and <2.3 Ma. In 2014, two simple burial dates for the Lower Bank, the earliest unit within Member 1, narrowed its age to between ca. 1.8 Ma and 2.2 Ma. A new dating program using the isochron method for burial dating has established an absolute age of 2.22 ± 0.09 Ma for a large portion of the Lower Bank, which can now be identified as containing the earliest Oldowan stone tools and fossils of Paranthropus robustus in South Africa. This date agrees within one sigma with the U-Pb age of 2.25 ± 0.08 Ma previously published for the flowstone underlying the Lower Bank and confirms a relatively rapid rate of accumulation for a large portion of the talus.

Systematic tool production and use is one of humanity\'s defining characteristics, possibly originating as early as >3 million years ago.1-3 Although heightened manual dexterity is considered to be intrinsically intertwined with tool use and manufacture, and critical for human evolution, its role in the emergence of early culture remains unclear. Most previous research on this question exclusively relied on direct morphological comparisons between early hominin and modern human skeletal elements, assuming that the degree of a species\' dexterity depends on its similarity with the modern human form. Here, we develop a new approach to investigate the efficiency of thumb opposition, a fundamental component of manual dexterity, in several species of fossil hominins. Our work for the first time takes into account soft tissue as well as bone anatomy, integrating virtual modeling of musculus opponens pollicis and its interaction with three-dimensional bone shape form. Results indicate that a fundamental aspect of efficient thumb opposition appeared approximately 2 million years ago, possibly associated with our own genus Homo, and did not characterize Australopithecus, the earliest proposed stone tool maker. This was true also of the late Australopithecus species, Australopithecus sediba, previously found to exhibit human-like thumb proportions. In contrast, later Homo species, including the small-brained Homo naledi, show high levels of thumb opposition dexterity, highlighting the increasing importance of cultural processes and manual dexterity in later human evolution.

Paleontology has long relied on assumptions about the genetic and developmental influences on skeletal variation. The last few decades of developmental genetics have elucidated the genetic pathways involved in making teeth and patterning the dentition. Quantitative genetic analyses have refined this genotype:phenotype map even more, especially for primates. We now have the ability to define dental traits with a fair degree of fidelity to the underlying genetic architecture; for example, the molar module component (MMC) and the premolar-molar module (PMM) that have been defined through quantitative genetic analyses. We leverage an extensive dataset of extant and extinct hominoid dental variation to explore how these two genetically patterned phenotypes have evolved through time. We assess MMC and PMM to test the hypothesis that these two traits reveal a more biologically informed taxonomy at the genus and species levels than do more traditional measurements. Our results indicate that MMC values for hominids fall into two categories and that Homo is derived compared with earlier taxa. We find a more variable, species-level pattern for PMM. These results, in combination with previous research, demonstrate that MMC reflects the phenotypic output of a more evolutionarily stable, or phylogenetically congruent, genetic mechanism, and PMM is a reflection of a more evolutionarily labile mechanism. These results suggest that the human lineage since the split with chimpanzees may not represent as much genus-level variation as has been inferred from traits whose etiologies are not understood.

Paranthropus boisei was first described in 1959 based on fossils from the Olduvai Gorge and now includes many fossils from Ethiopia to Malawi. Knowledge about its postcranial anatomy has remained elusive because, until recently, no postcranial remains could be reliably attributed to this taxon. Here, we report the first associated hand and upper limb skeleton (KNM-ER 47000) of P. boisei from 1.51 to 1.53 Ma sediments at Ileret, Kenya. While the fossils show a combination of primitive and derived traits, the overall anatomy is characterized by primitive traits that resemble those found in Australopithecus, including an oblique scapular spine, relatively long and curved ulna, lack of third metacarpal styloid process, gracile thumb metacarpal, and curved manual phalanges. Very thick cortical bone throughout the upper limb shows that P. boisei had great upper limb strength, supporting hypotheses that this species spent time climbing trees, although probably to a lesser extent than earlier australopiths. Hand anatomy shows that P. boisei, like earlier australopiths, was capable of the manual dexterity needed to create and use stone tools, but lacked the robust thumb of Homo erectus, which arguably reflects adaptations to the intensification of precision grips and tool use. KNM-ER 47000 provides conclusive evidence that early Pleistocene hominins diverged in postcranial and craniodental anatomy, supporting hypotheses of competitive displacement among these contemporaneous hominins.

KNM-ER 47000 is a fossil hominin upper limb skeleton from the Koobi Fora Formation, Kenya (FwJj14E, Area 1A) that includes portions of the scapula, humerus, ulna, and hand. Dated to ∼1.52 Ma, the skeleton could potentially belong to one of multiple hominin species that have been documented in the Turkana Basin during this time, including Homo habilis, Homo erectus, and Paranthropus boisei. Although the skeleton lacks associated craniodental material, the partial humerus (described here) preserves anatomical regions (i.e., distal diaphysis, elbow joint) that are informative for taxonomic identification among early Pleistocene hominins. In this study, we analyze distal diaphyseal morphology and the shape of the elbow region to determine whether KNM-ER 47000 can be confidently attributed to a particular species. The morphology of the KNM-ER 47000 humerus (designated KNM-ER 47000B) is compared to that of other early Pleistocene hominin fossil humeri via the application of multivariate ordination techniques to both two-dimensional landmark data (diaphysis) and scale-free linear shape data (elbow). Distance metrics reflecting shape dissimilarity between KNM-ER 47000B and other fossils (and species average shapes) are assessed in the context of intraspecific variation within modern hominid species (Homo sapiens, Pan troglodytes, Gorilla gorilla, Pongo pygmaeus). Our comparative analyses strongly support attribution of KNM-ER 47000 to P. boisei. Compared to four other partial skeletons that have (justifiably or not) been attributed to P. boisei, KNM-ER 47000 provides the most complete picture of upper limb anatomy in a single individual. The taxonomic identification of KNM-ER 47000 makes the skeleton an important resource for testing future hypotheses related to P. boisei upper limb function and the taxonomy of isolated early Pleistocene hominin remains.

When measured as a ratio of mean midshaft diameter to bone length, the OH 8 fossil hominin foot exhibits a metatarsal (Mt) robusticity pattern of 1 > 5 > 3 > 4 > 2, which differs from the widely perceived \"common\" modern human pattern (1 > 5 > 4 > 3 > 2); African apes generally exhibit a third pattern (1 > 2 > 3 > 4 > 5). Largely because of the relative ranking of Mt2 and Mt5, OH 8 metatarsals structurally resemble the pattern exhibited by bipedal humans more than the pattern of quadrupedal and climbing African apes. Considering only these three phenotypes, however, discounts the potentially important functional implications of variation in modern human (and African ape) metatarsal robusticity patterns, suggesting that they are not useful for interpreting the specific biomechanics of a bipedal gait in fossils (i.e., whether it was modern human-like or not). Using computed tomography scans to quantify metatarsal midshaft cross-sectional geometry in a large sample of Homo (n=130), Gorilla (n=44) and Pan (n=80), we documented greater variation in metatarsal robusticity patterns than previously recognized in all three groups. While apes consistently show a 1 > 2 > 3 > 4 > 5 pattern in our larger sample, there does not appear to be a similarly precise single \"common\" human pattern. Rather, human metatarsals converge towards a 1 > 4/5 > 2/3 pattern, where metatarsals 4 and 5, and metatarsals 2 and 3, often \"flip\" positions relative to each other depending on the variable examined. After reassessing what a \"common\" human pattern could be based on a larger sample, the previously described OH 8 pattern of 1 > 5 > 3 > 4 > 2 is only observed in some humans (<6%) and almost never in apes (<0.5%). Although this suggests an overall greater similarity to (some) humans than to any ape in loading of the foot, the relatively rare frequency of these humans in our sample underscores potential differences in loading experienced by the medial and lateral columns of the OH 8 foot compared to modern humans.